Basics of ac drives

Introduction to AC Drives Introduction
© 1997 Square D Company, All Rights Reserved Page 1
Introduction to AC
Drives
Table of Contents
Training Program Overview------------------------------------------------------------------------------------------1
Self Assessment Study Guide---------------------------------------------------------------------------------------5
Chapter 1 - AC Motor Fundamentals -------------------------------------------------------------------------11
Chapter 2 - AC Drive Fundamentals --------------------------------------------------------------------------29
Chapter 3 - Square D AC Drive Products -------------------------------------------------------------------43
Chapter 4 - AC Drive Characteristics & Types -----------------------------------------------------------63
Chapter 5 - Helping Customers -------------------------------------------------------------------------------87
Appendix A - Self Assessment Study Guide Answers-------------------------------------------------------93
Glossary of Terms----------------------------------------------------------------------------------------------------99
Final Test ------------------------------------------------------------------------------------------------------------- 139
ALTIVAR is a registered trademark of the Square D Company
OMEGAPAK is a registered trademark of the Square D Company
MAG-GARD is a registered trademark of the Square D Company

Page 2 © 1996 Square D Company, All Rights Reserved
Introduction to AC Drives
This module, “Introduction to AC Drives,” is designed to familiarize the participant with AC motor
theory, AC drive theory, Square D AC drive products and their enclosures, and provide job aids
for assisting customers.
Prerequisites
Module 1 - Fundamentals of Electricity - The first module introduces some important concepts
that need to be understood in order to effectively learn the material in “Introduction to AC
Drives.”
Module 2 - Introduction to Distribution Equipment - This module deals with products such as:
NEMA enclosures, Digest overview, and circuit breakers.
Module 3 - Introduction to Control Products - You should review the following chapters
before proceeding with this course if you feel uneasy about their content:
•••• Chapter 1 - Overview of Motor Control
and/or
You are strongly encouraged to complete the AC Motor Theory Course (AUTM 100) which
is available on either CD ROM or 3 1/2” disk. This program provides an in-depth coverage of
AC motor theory which is necessary in order to understand the relationship between the motor
and the AC drive which controls it.
Training Program Components
There are five chapters, including an appendix and glossary, in this course. They are:
• Chapter 1 - Introduction to AC Motors - This chapter provides an overview of the
components of an AC motor, how the motor operates and AC motor terms and concepts.
• Chapter 2 - AC Drive Fundamentals - This chapter covers:
• Advantages of AC drives over other methods of motor control
• Applications for AC drives
• AC drive theory
• Load and braking considerations
• Chapter 3 - Square D AC Drive Products - This chapter covers the features and benefits of
the Altivar 16, 66, 56, and 18 AC drive products. The Omegapak 8803 and 8804 products
are also covered.
• Chapter 4 - AC Drive Enclosure Characteristics/Types - This chapter discusses the
different types and characteristics of enclosures available for Square D drive products.
• Chapter 5 - Helping Customers - This chapter provides the participant with job aids for
dealing with customer drive questions.

• Glossary of Terms - This glossary contains the meanings of many terms common to AC
drives.
Each chapter in the student workbook includes learning objectives.
Self-Check Questions and Self-Check Answers have been included within each chapter. They
will enable you to check your understanding of the material presented to you.
How to Use the Student Workbook
The student workbook provides a self-study training process that is designed to help you learn
with or without assistance from a trainer. You will find this workbook becomes a valuable
reference tool after you have completed the training, so keep it handy. For the most effective
use of this training process, follow the steps on the next page.

Steps to Complete Introduction to AC Drives
1.
Complete the Self Assessment Study Guide,
if required, and review the answers with those
in the back of this workbook.*
2.
For each chapter you want to review, read
through the chapter in the workbook. Feel free
to take notes or highlight in your workbook.
3.
Complete the Self Check Test and review
the answers.
4.
Repeat steps 2 - 3 until you complete the
training program. Then go to step 5.
5.
Complete the Final Test for
Introduction to AC Drives
6.
Complete the enclosed scannable answer
form and return by mail to OD&E.

Introduction to AC Drives Self Assessment Study Guide
SELF ASSESSMENT
STUDY GUIDE

SELF ASSESSMENT STUDY GUIDE
Select the best answer:
1. The armature of a motor consists of ____ .
A. the housing and rotor
B. the shaft and stator
C. the stator and housing
D. the shaft and rotor
2. The magnetic fields of the stator and rotor are changed according to the ___ .
A. the current applied to the motor
B. frequency of the AC voltage applied to the motor
C. the frequency of the current applied to the motor
D. the wattage applied to the motor
3. The speed of the rotor is determined by the ___ .
4. The difference between a motor’s synchronous and actual rotor speed is called: _____ .
A. Variable torque
B. Dynamic speed
C. Slip
D. Magnetic flux
5. The torque a motor produces is directly related to ____ .
6. The maximum torque that a motor can produce is called: _____ .
A. Full load torque
B. Constant torque
C. Breakdown torque
D. Overload toque
7. A motor’s service factor indicates the: _____ .
A. Approximate life expectancy of the motor if applied within the rated nameplate
parameters
B. The NEMA rating of the motor which is comparable to the torque performance of the
motor.
C. Electrical power supplied to the motor.
D. Overloads which may be carried by the motor without exceeding the maximum
temperature recommended for the insulation

8. Match the components of an AC drive with their function:
Inverter A. This section smoothes rectified DC before it goes
to the next section.
DC bus filtering B. This section changes DC into an adjustable frequency
synthetic AC
Converter C. This section changes 60 Hz AC power into DC
9. The difference between a soft start and an AC drive is: _____ .
A. That the soft start reduces voltage and current at startup
B. That an AC drive controls motor startup by reducing startup torque.
C. That a soft start can be used in place of an AC drive
D. All of the above
E. None of the above
10. Maintaining the volts per Hertz ratio is necessary because: _____ .
A. In order to accurately measure a given motor’s speed then the ratio of both the voltage
and frequency must be maintained.
B. When a motor is running at less than full speed maintaining this ratio provides a method
of keeping the magnetic flux constant, thus producing full load-torque.
C. The voltage and frequency coming from the power generating station may varies in both
voltage and frequency.
D. The horsepower of the motor is dependent upon this ratio.
11. With a constant torque load: _____ .
A. Torque remains the same as the speed changes.
B. Horsepower varies inversely with the speed.
C. Torque remains the same as the current changes.
D. All of the above.
12.________ AC drives can only be ordered as replacements to existing equipment.
A. ALTIVAR
B. OMEGAPAK
C. ALTIVAR and OMEGAPAK
D. There are no limited offerings with AC drives
13. The complete ALTIVAR family consists of _______ .
A. ALTIVAR 16, 26, 55, and 67
B. ALTIVAR 8803, 8804, 16, and 18
C. ALTIVAR 8803 and 8804
D. ALTIVAR 16, 18, 56, and 66

14. The ALTIVAR drives meet _______ standards.
A. ISO 9000 series, and UL, CSA, IEC, VDE
B. UL, CSA, IEC, VDE
C. ISO 9000, ISO 3000 series, and UL, VDE
D. ISO 9007 series, and UL, CSS, ICC, VDE
15. _______ are the major components for Dynamic Braking.
A. Jumper J-12 to switch a resistor circuit in and out, and a separately mounted brake
B. A separately mounted semi-conductor circuit and resistor R-7
C. A power semi-conductor to switch resistor circuit in and out, and a separately mounted
braking resistor
D. A power semi-conductor to switch resistor circuit in and out, and three separately
mounted braking resistors
16. An open type drive is bought as _____.
A. As a component piece
B. As a total Square D enclosure
C. As a total Square D MCC
D. All of the above
17. _____ drive(s) can be used for open type applications.
A. OMEGAPAK 8803 and 8804
B. ALTIVAR 16, 18
C. ALTIVAR 16, 18, 56, and 66
D. ALTIVAR 16, 18, 56, 66, and OMEGAPAK 8803 and 8804
18. Enclosed type drives are manufactured at the _____.
A. Square D Raleigh plant in North Carolina
B. Square D Columbia plant in South Carolina
C. Square D Seneca plant in South Carolina
D. Square D Oxford plant in Ohio
19. _____ drive(s) can be used for MCC applications.
A. OMEGAPAK 8803
B. ALTIVAR 66
C. ALTIVAR 16
D. ALTIVAR 56
20. The MCC drive packages can be from _____.
A. 1-50HP, 220V constant/variable torque or 1-25HP, 480V variable torque low noise
B. 1-800HP, 240V constant/variable torque or 1-75HP, 400V variable torque high noise
C. 1-50HP, 480V constant/variable torque or 1-250HP, 480V variable torque no noise
D. 1-200HP, 480V constant/variable torque or 1-75HP, 480V variable torque low noise

21. Enclosed Type drives are offered in _____.
A. NEMA Type 1 and Type 12 enclosures
B. NEMA Type 1, Type 3, and Type 12 enclosures
C. NEMA Type 12 enclosures
D. NEMA Type 4 and Type 12 enclosures
TURN TO APPENDIX A FOR ANSWERS

Introduction to AC Drives Chapter 1 - AC Motor Fundamentals
Chapter 1 - AC Motor
Fundamentals
LEARNING OBJECTIVES
The participant will:
• Be able to identify the components of an AC motor
• Understand how an AC motor operates
• Understand AC motor terms and concepts
• Identify meaning of motor nameplate terms

PREREQUISITES
AC drives control AC motors. It’s that simple. So, in order to understand what AC drives are, how
they work and where they are applied, you need to first understand the parts of an AC motor and
how AC motors function. If you are unsure about AC motor theory here are few suggestions on
where you can go to get that information:
• If you are enrolled in Square D Technical Institute, then motor theory was covered in Module
3. You may want to review that module before continuing on with this course.
• For a more in-depth coverage of AC motors (whether or not you are part of Square D
Technical Institute or not) you’ll find that Square D has available an excellent self paced
course on AC Motor Theory - Course # AUTM 100. It is highly recommended that you
complete this course prior to starting this course on AC drives. AUTM 100 is available on
either 3 1/2” disks or a CD ROM.
While we will present a brief review of AC motor theory and terminology, it is assumed that you
meet one or more of the above prerequisites and have a clear understanding of AC motors.
REVIEW OF AC MOTOR THEORY
Some of the reasons you need to understand AC motor theory in order to understand AC drives
are:
• To provide customer satisfaction
 The AC drive and the AC motor work together as a system
• To select the correct drive
 Must have knowledge of NEMA A, B, C, and D motor speed and torque characteristics
• To ensure desired motor performance
 Because an AC drive effects:
• Speed, torque, current, voltage, heating and horsepower
We all know that there is a relationship between a motor, a machine and motor control. The
machine does the actual work. The motor is the device which causes the machine to operate.
And, the motor controller is the intelligence that directs the motor. That is, it determines when
and in what direction the motor will operate. And, it may provide protection for the motor, branch
circuits and the operator.
Did you know that the average household has more than 25 electric motors. A medium sized
manufacturing plant, such as the Square D plant in Raleigh, NC may have from 4,000 to 5,000
electric motors. And a large automated plant, like an automobile assembly plant could have
25,000 electric motors in it.
And now, let’s get on with learning about the fundamentals of AC motors.

AC MOTOR FUNDAMENTALS
Components Of An Electric Motor
Electric motors are really quite simple. There are only four basic parts to an electric motor:
• There is the housing or external case that surrounds the other components.
• Mounted inside the housing is the stator. The stator is the stationary or non-moving part of
the motor’s interior. It is made up of wire windings. The moving parts of the motor are the
rotor and the shaft.
• The rotor, like the stator, also has windings.
• The rotor is connected to the fourth component, the shaft. The shaft is a metal rod held in
position within the stator by bearings connected to the case. The bearings allow the shaft to
rotate inside the stator. The rotor and shaft are often referred to as the armature of the
motor.
How An Electric Motor Operates
The electric motor operates by converting electrical energy into mechanical energy. Let’s
represent the motor’s stator as an iron block “S” and the rotor as an iron block “R”. Both of these
iron blocks are wrapped with wire coils. When electrical current is passed through the wire coils,
an electromagnetic field is created and the iron blocks become magnetized. All magnets have a
North and a South pole. A North pole is always trying to get next to a South pole and visa versa.
Two North or two South poles will push away or repel each other. In other words, opposite poles
attract and like poles repel. It’s this magnetic pull and push principle that makes an electric motor
operate.
Suppose that “S” is fastened such that it cannot move. On the other hand, “R” is allowed to move
freely. When electricity is passed through the coils and the blocks are magnetized, the opposite
poles try to pull together. Block “R” will move towards block “S.” If the blocks get together the
movement will stop. What if block “S” were mounted in such a way that block “R” couldn’t
contact it? Block “R” would move until it’s positive pole were as close as it could get to block “S”
and then motion would stop.
Housing
Stator Rotor
Shaft
S S RR
N S N S N S S N

Let’s add more “S” blocks (S1, S2, S3, and S4). If S1 were demagnetized just as “R” reached it,
and S2 is magnetized, “R” would continue moving toward “S2.” If this same process of
demagnetizing and magnetizing S1, then S2, then S3 and finally S4, were continued then block
“R” would be moving all the time until it reached S4.
In an electric motor the “S” magnets are formed in a circle and the “R” magnet is placed inside
this circle and is attached to a shaft. The stator and rotor are magnetized as current flows
through the coil windings. The rotor moves so that the opposite poles of the windings can try to
move closer to the stator magnets. Just as the magnets are close the magnetic field moves on in
the stator, and the rotor chases after it. Since the rotor and shaft are fastened together, the shaft
moves. The rotation of the shaft is the mechanical energy created by the conversion of the
electrical energy by the motor.
To summarize, the rotor “chases after” the changing magnetic field of the stator which causes
the rotor and shaft to rotate. The magnetic fields of the stator and rotor are changed according to
the frequency of the AC voltage applied to the motor. Changing the frequency of the voltage
applied will alter the speed at which the stator’s magnetic fields change. This will, in turn, change
the speed of the rotor. Changing the current will alter the strength of the magnetic fields of the
rotor and stator. The stronger the magnetic fields the greater the turning force applied by the
rotor to the shaft. This twisting or turning force is called torque.
S4
N S
S3
N S
S2
N S
S1
N S
R
N S
S
S1 S4
S2 S3
Rotor
N
N
N
N
S
S
S
S
N
ShaftStator

Types of AC Motors
The four principle types of motors (not including single phase types) found in commercial and
industrial applications are: squirrel cage induction, wound rotor induction, synchronous, and
direct current (dc).
The squirrel cage induction motor is by far the most widely used motor because of its low cost
and proven reliability. The wound-rotor induction motor has been used in applications that
require high starting torque, controlled starting torque, or speed control. The synchronous
separately excited motor has been used in high-horsepower applications where it is
advantageous to overexcite the motor to provide power factor correction in an industrial facility.
The synchronous permanent magnet and reluctance motor is used in applications that need
precise speed for a number of motors operating in combination.
But the squirrel cage motor is by far the simplest, most reliable, least expensive, most readily
available and easiest to maintain. In addition, with improvements in AC drives, squirrel cage
motors are now applied in the majority of the applications your customers are involved with.
MOTOR TERMS AND CONCEPTS
Motor Terms and Concepts
• Electric service is a term used to describe or define electrical power supplied to a motor.
The selection of motor control products depends upon the information that is included as part
of electrical service. This information includes:
 Current - the current used by the motor is either AC or DC. Square D currently only
makes drives for AC motors.
 Phase - a motor can be powered by either single or polyphase electric power. The term
polyphase means more than one phase and typically refers to 3 phase.
 Frequency - is the number of electrical pulses that are transmitted over a given period
of time. Frequency is measured in hertz (Hz) or cycles per second (cps).
V
t
In this example, you see that the voltage builds from zero, in the positive direction up to
a peak positive value of + 460 V. Then it starts to decline in value until it reaches zero
volts again. Next the voltage starts in the negative direction until it reaches a peak value
of
- 460 V. Finally the voltage starts to move back in the positive direction until it reaches
zero volts. The change in voltage from zero to a peak positive value, back to zero, to a
peak negative value and back to zero is called 1 cycle. It has taken time for a cycle to
occur. In our example, that time is one second. Frequency is measured in terms of
One Second
0V
- 460V
Volts
Time
+

cycles per second and the frequency of this example is one cycle per second. The more
common term for frequency is called Hertz. One Hertz equals one cycle per second.
Alternating current completes these cycles very rapidly and the number of cycles per
second is known as the frequency. Throughout the United States AC current typically
goes through a cycle 60 times per second, so the frequency is 60 Hertz. In many foreign
countries, the AC current cycles 50 times per second, so the frequency is 50 Hertz.
 Voltage - electric motors are designed to operate using a specific voltage. Motor control
devices are also rated according to the voltage that can be applied to them.
• Locked rotor current (LRC) is the current flow required by a motor in order for the motor to
start. Locked rotor current may be called Locked rotor amps (LRA).
• Full Load Amps (FLA) - this is the current flow required by a motor during normal operation
to produce its designed HP. Full load amps (FLA) is also called Full Load Current or (FLC).
• Speed (in revolutions per minute), Torque (ft.lbs.) and Horsepower (HP) are all terms that
are used to define motor performance:
Let’s start with Horsepower. Motors and engines are measured in horsepower. Horsepower
is a standard unit of power which is used to measure the rate at which work is done. One
Horsepower is the equivalent of 550 foot-pounds per second --- that is the ability to lift 550
pounds one foot in one second. For example, if an electric motor can lift 550 pounds 10 feet
and it takes 10 seconds, then the motor has a horsepower rating of 1 hp.
In any electric motor the motor torque can be multiplied by the motor speed and the product
divided by 5250 (a constant) to determine the rated horsepower.
Torque (ft.lbs.) X Speed (RPM)
HP =
5250
Before continuing the discussion about the horsepower equation, let’s look at torque.
Torque is formally defined as: “the force tending to rotate an object, multiplied by the
perpendicular radius arm through which the force acts.” In the case of a motor, torque is the
force which acts on the shaft and causes rotation. Remember that the amount of torque
created is directly related to the amount of current applied to the motor. The greater
the current the stronger the magnetic fields of the stator and rotor, and therefore the greater
the turning force of the shaft. A motor is a dumb device. As the load is increased on the
shaft, the motor will draw more current (to increase the torque) to try and keep the load
moving. If the load were to continue to be increased, the motor will literally destroy itself
trying to create the necessary torque to move the load.
Consider how a motor generates torque vs how it generates Speed. Motor speed is
measured in rpm (the revolutions per minute the rotor turns) and is the speed at which the
rotor rotates inside the stator. This rotational speed will depend upon the frequency of
the AC voltage applied and the number of stator poles. If the motor has no load, this
speed will approach the synchronous speed of the stator field.
• Synchronous speed is the speed of an AC induction motor’s rotating magnetic field. It is
determined by the frequency applied to the stator and the number of magnetic poles present
in each phase of the stator windings. This can be expressed by the formula:

120 X Frequency
Synchronous Speed =
Number of Poles
For example:
120 X 60 Hz
Synchronous Speed = = 1800 rpm
4 pole motor
• Motor Slip
Slip is the difference between the rotating magnetic field speed in the stator and the rotor
speed in AC induction motors. This is usually expressed as a percentage of synchronous
speed. If the rotor were rotating at exactly the same speed as the stator’s rotating magnetic
field (for example, 1800 rpm) then no lines of magnetic force would be cut, no voltage would
be generated in the rotor and no current would be present. However, if the rotor slows down
by 50 rpm it would now be running at 1750 rpm vs 1800 rpm of the stator field. The rotor
bars are now cutting the rotating field at a 50 rpm rate. Now voltage and current would be
generated in the rotor, with a resulting magnetic flux pattern. The interaction of these
magnetic fields would produce torque. The difference between the synchronous and actual
rotor speeds is called slip.
• Torque vs Speed Relationship:
Torque, remember is a force exerted on the motor’s shaft when a load is added to the rotor.
The tendency is for the rotor to slow down, which will create more slip (difference between
the stator magnetic field speed and rotor speed), thus creating more torque within the motor.
As the load is increased, the rotor will continue to slow down, which would result in even
greater slip as the rotor lags behind the synchronous speed of the rotor. The increased
resistance to rotation increases the slip and therefore increases the torque.
Synchronous Speed - Rotor Speed
Slip = X 100
Synchronous Speed
1800 rpm - 1750 rpm
X 100
1800 rpm
Slip = 2.78%
Rotor Speed
Stator
Synchronous
Speed
Slip

Now, lets go back to the horsepower equation again.
HP =
5250
This formula will help you select the proper motor for a job. Notice the relationship
between torque and speed. It is obvious that a 5 hp motor, designed to run at high speed,
will have very little torque. To maintain the equation, torque must decrease as speed
increases:
HP =
5250
Conversely, a 5 hp motor with high torque must run at a slow speed.
HP =
5250
An important relationship for you to remember is that:
SPEED IS RELATED TO FREQUENCY
and
TORQUE IS RELATED TO CURRENT
You’ve already seen that increasing the frequency at which the magnetic fields change will
cause an increase in the speed of rotor and shaft rotation. If the frequency were decreased,
the motor speed would slow down.
If the current drawn by the stator and rotor is increased, this would cause a strengthening of
the magnetic fields. This, in turn, would cause the torque generated by the motor to increase.
Likewise, if the current were decreased, the torque would be decreased as well.
In fact the horsepower formula can also be expressed in electrical terms of voltage and
current, as:
Volts X Amps X 1.732 X Power Factor X Efficiency
HP (Output) =
746
• Constant and Variable Torque
If you look at a motor’s usage based on the torque requirements of an application, you will
find that you may need constant torque or variable torque. One application might require
normal starting torque and a normal running torque, for example, a drill machine. This

category requires that a motor starts with a normal amount of torque and then continues to
run at the required speed.
Another application category might require a high starting torque but a normal running
torque. For example, a conveyor that is first loaded up and then started. When the loaded
conveyor is started the motor must provide a big push of torque to get the conveyor and its
load moving. Once moving, inertia has been overcome and the resistance of friction falls,
therefore normal running torque provides adequate power to keep the conveyor running.
The third torque category would be an application that requires a very high starting torque,
and a normal running torque.
Starting and running torque can be plotted. As the starting torque increases, motor speed
decreases --- remember the equation: speed times torque equals horsepower. As torque
increases, the motor speed decreases.
Notice that at zero speed the starting torque is very high. This is needed to get the load
moving from a dead stop. As the speed increases the torque curve fluctuates until the full
load torque and full load speed are reached.
• The breakdown torque is the maximum torque that a motor can produce. Higher torque
requirements will slow motor speed to a stop. Breakdown torque is the point where speed
stops as torque requirement increases.
• Full load torque is the amount of torque developed by the motor at rated speed and rated
current. The rated speed and current values can be found on the motor nameplate.
• NEMA Design Ratings
The NEMA ratings refer to torque ratings. These rating apply to motors which are started
across the line.
Locked Rotor Torque
Breakdown Torque
Full Load Torque

The design areas of the nameplate refer to the NEMA rating of the motor which is
comparable to the torque performance of the motor. NEMA has five design ratings of AC
induction motors. Each of these designs has a different characteristic for starting current,
locked rotor current, breakaway torque, and slip. These designs are NEMA A, B, C, D, and
E. Each has a distinct speed vs torque relationship and different values of slip and starting
torque.
The most common is the NEMA Design B motor.
The NEMA B motor’s percentage of slip ranges from 2 to 4%. It has medium values for
starting or locked rotor torque, and a high value of breakdown torque. This type of motor is
very common in fan, pump, light duty compressors, various conveyors, and some light duty
machines. The NEMA B motor is an excellent choice for variable torque applications.
The NEMA A motor is similar in many ways to the NEMA B motor. It typically has a higher
value of locked rotor torque and its slip can be higher
NEMA B
NEMA A

NEMA C motors are well suited to starting high-inertia loads. This is because they have high
locked rotor torque capability. Their slip is around 5%, and their starting current requirement
is average.
The NEMA D motor is found in heavy duty, high-inertia applications. It has high values of
slip (up to 8%), and very high locked rotor torque capability. Typical applications include
punch presses, shearing machinery, cranes, and hoists.
NEMA C
NEMA D

• Motor Load - a motor provides the conversion of electrical energy to mechanical energy
that enables a machine to do work. The energy that a machine requires from a motor is
known as the motor load. For example, the motor in a clothes dryer turns the dryer drum.
The energy required by the dryer motor to turn the drum is called the dryer’s motor load.
• Motor Overload - An electric motor for all its other fine qualities has no intelligence and will
literally work itself to death. If there is a heavy load on a motor, say when the clothes dryer is
full of clothes, the motor will try to produce whatever torque is needed to keep the dryer
drum turning. Because the motor load may be increased above normal, a motor overload
condition exists. More torque is required from the motor to turn the drum, so the motor draws
more current to produce more energy. The higher than normal current flow, which is above
the FLC, increases the temperature in the dryer motor. The electric motor could be damaged
when the temperature rises above its designed limit.
• Motor Cooling - Whenever electrical current is passed through an electrical motor there is a
buildup of heat. The amount of heat produced is a function of the work, or loading, done by
the motor; the type of electrical signal being sent to the motor; and the eventual changes due
to bearing wear and friction. Whenever AC drives are used to control motors it means that
the speed of the motor is going to be changed. And, depending upon motor loading, special
attention needs to be given to how the motor is going to be cooled. Generally speaking, less
speed means less cooling.
Different motor cooling designs are available:
• Many motors are sized for a particular application, or horsepower rating, so that the heat
produced from the current can be accepted and dissipated by the metal content of the
motor. Normal convection and radiation dissipate the heat with the aid on an internal
mixing fan. These motors are classified as “open drip-proof” or “totally enclosed
nonventilated (TENV).”
• Other electric motors incorporate a fan blade that rotates at the same speed as the
motor shaft. This fan blows air across the outside of the motor, cooling it as it runs.
However, if an AC drive is used, the lower in speed the motor is made to run, the slower
the cooling fan will run also. This can result in a buildup of heat in the motor. These
motors are called “totally enclosed fan-cooled (TEFC).”
• Some types of motors use elaborate means for cooling. These are called “totally
enclosed water-to-air cooled,” “totally enclosed air over,” and “totally enclosed
unit cooled.” Obviously, the more complex the cooling method, the more expensive the
actual motor will be.
There are a couple of different strategies used for selecting a motor that will be adequately
cooled during operation:
• One approach is to size the motor with a service factor. A service factor of 1.15 means
that the motor has 15% more capacity when operating conditions are normal for voltage,
frequency, and ambient temperature. This 15% extra capacity means that the motor is
built and sized when the duty cycle is severe, or the loading and speed range is
moderate.
• Another strategy is to simply go up in horsepower, which is how motors are sized. This
might put a motor into a larger frame designation, thereby making it weigh more and
allowing it to handle a greater amount of heat.

The concern of both of these strategies is that you could end up with a motor that is well
oversized for the application. This would cause wasted energy and increase the cost of the
motor. Another answer might be to add auxiliary cooling equipment to the motor.
MOTOR NAMEPLATE DATA
Motor Nameplate Data
Squirrel cage motors, like any other type of electrical equipment, require proper application
for successful operation. Understanding the nameplate information, which identifies the
motor’s important features and characteristics, will aid considerably in proper application.
A nameplate is attached to each AC motor and includes information such as:
• Full load speed
• Torque ratings
• Type of enclosure
• Type of insulation
• Temperature Rise Rating
• Service Factor
• Time Rating
• Locked Rotor KVA
• Frame sizes - In 1972 NEMA Standards included numbers for various frame sizes that
range from 140 to 680. These are commonly called “T” frame motors. There is a relation
between the numbers assigned and their frame dimensions. For example, the first two digits
of the number equal four times the dimension in inches from the center line of the shaft to
the bottom of the feet. A series of letters is used immediately following the frame size
number to help identify certain features.
The motor nameplate identifies a frame size number and letter which are indicative of
dimensions and some features. NEMA has specified certain dimensions for motor frame
sizes -- up to 200 hp. These are identified by the numbers listed below.
Frame Number Series
140 220 400
160 250 440
180 280 500
200 320 580
210 360 680
The physical size and consequently the cost of a squirrel cage motor is determined by its
frame size. The actual horsepower rating for each frame size will vary and will be
determined by several design parameters, which have been standardized by NEMA. Above
approximately 200 hp, electrical standards apply for motors, but the frame sizes are not
standardized.
• Full Load Speed - The motor nameplate identifies the rated full load speed. This speed is
one of the key considerations in determining the motor horsepower required for a given load.
The motor synchronous speed is influenced by the number of magnetic poles in the stator.

The synchronous speed is slightly higher than the motor shaft speed. As the number of poles
in a motor design is increased, the rated synchronous speed is decreased per the formula:
120 X Frequency
Synchronous Speed =
Number of Poles
Because of this the physical size of a squirrel cage motor is inversely related to its speed ---
meaning, the frame size may be larger as the rated synchronous speed becomes lower. For
example, a 100 hp, 600 rpm twelve pole motor will be considerably larger than a 100 hp,
3600 rpm two pole motor.
• Torque Ratings - The motor nameplate identifies the type of design motor (A, B, C, D, E),
which is indicative of its locked rotor and peak torque ratings. In addition the nameplate
identifies the rated horsepower at rated speed and from this information, rated full load
torque can be determined. The full load torque rating will determine the full load current at
rated voltage. The physical size of the motor is directly related to its full load torque rating.
For example, in comparing the torque ratings of the 100 hp 600 rpm and 3600 rpm motors in
the full load speed example, you may recall that motor horsepower is proportional to torque
time speed. Since the speed rating of the larger twelve pole motor is 1/6 that of the two pole
motor, the torque rating is approximately six times that of the two pole motor.
• Enclosures and Ventilation - The motor nameplate usually identifies the type of enclosure
and ventilation system, such as open type self-ventilated, totally enclosed fan cooled
(TEFC), totally enclosed non-ventilated (TENV) and others. See “Motor Cooling” in previous
discussion entitled “Motor Terms and Concepts.”
• Insulation and Temperature Rise Ratings - The motor nameplate identifies the Class of
Insulation material used in the motor and its rated ambient temperature. Various types of
materials can be used for insulation which are defined as Class A, Class B, Class F and
Class H. IEEE Standards list temperature ratings as follows:
Class A - 105° C
Class B - 130° C
Class F - 155° C
Class H - 180° C
When the rated temperature of the insulation materials is exceeded, it is estimated that the
insulation life is decreased by 1/2 for every 10 degrees above the rating. By using higher
temperature rated materials, more heat losses in the motor can be tolerated. Consequently,
the horsepower rating of a motor can be increased in a given frame size.
NEMA Standards specify permissible temperature rises above a 40° C ambient for motors.
This is determined by the type of insulation in the motor, and other motor design and
application considerations. Some motors operate at higher temperatures then others, but
none should exceed the temperature rating of the insulation.
• Service Factor - A motor is rated by the manufacturer to produce a certain HP over a long
period of time without damage to the motor. However, occasionally a motor might be
operated intentionally or unintentionally above the rated HP. To protect against motor
damage caused by the occasional excess current an electric motor is usually built with a
margin of safety. The margin of safety is called the motor’s service factor.

The motor nameplate identifies a service factor; 1.0 or 1.15. This indicates overloads which
may be carried by a motor under nameplate conditions without exceeding the maximum
temperature recommended for the insulation. For example, a 100 hp motor with a 1.15
service factor can sustain a 15% overload (100 X 1.15 = 115 hp) continuously and will not
exceed the temperature rating of the insulation in the motor, provided the ambient
temperature is no greater than 40° C. Frequently motors are specified with 1.15 service
factor to provide additional thermal capacity.
• Time Ratings - The motor nameplate identifies its time rating which can be continuous duty
or short times, such as 60 minutes, 30 minutes, 15 minutes and 5 minutes. Obviously, at a
specified horsepower, a motor operating continuously will generate more total losses and will
require a larger frame size, compared to a motor operating intermittently. The short time
ratings indicate the motor can carry the nameplate loads for the time specified without
exceeding the rated temperature rise. After the short time, the motor must be permitted to
cool to room temperature.
• Locked Rotor KVA - The motor nameplate identifies the locked rotor KVA with a code letter
- A thru V. The locked rotor KVA may be a consideration when applying motors where
limitations exist in the power distribution system. NEMA Standards have designated inrush
KVA’s for the various code letters.

SELF CHECK QUESTIONS AND EXERCISES
1. Match the parts of an AC motor with their correct description:
_____ Rotor A. External case that surrounds the motor.
_____ Housing B. A metal rod mounted in the case and supported by
bearings.
_____ Stator C. A rotating iron core with wire windings. It is attached
to the shaft.
_____ Shaft D. A stationary iron core with wire windings which is
attached to the case.
2. Match the motor term with its definition
_____ Torque A. Speed is related to frequency and torque is
related to current.
_____ Synchronous Speed B. The difference between the rotating magnetic
field speed in the stator and the rotor speed.
_____ Slip C. The force tending to rotate an object. A turning
force applied to a shaft, tending to cause
rotation.
_____ Torque vs speed relationship D. The speed of an AC induction motor’s rotating
magnetic field.
True or False
3. _____ The most common type of AC motor is the wound rotor induction motor.
4. _____ Locked rotor current is the current flow required by a motor in order for it to start.
5. _____ Horsepower is a unit of power used to measure the rate at which work is done.
6. _____ NEMA design ratings for motors refer to motor current and voltage ratings.

SELF CHECK ANSWERS
1. Match the parts of an AC motor with their correct description:
C Rotor A. External case that surrounds the motor.
A Housing B. A metal rod mounted in the case and supported by bearings.
D Stator C. A rotating iron core with wire windings. It is attached
to the shaft.
B Shaft D. A stationary iron core with wire windings which is
attached to the case.
2. Match the motor term with its definition
C Torque A. Speed is related to frequency and torque is
related to current.
D Synchronous Speed B. The difference between the rotating magnetic
field speed in the stator and the rotor speed.
B Slip C. The force tending to rotate an object. A turning
force applied to a shaft, tending to cause
rotation.
A Torque vs speed relationship D. The speed of an AC induction motor’s rotating
magnetic field.
True or False
3. F The most common type of AC motor is the wound rotor induction motor.
4. T Locked rotor current is the current flow required by a motor in order for it to start.
5. T Horsepower is a unit of power used to measure the rate at which work is done.
6. F NEMA design ratings for motors refer to motor current and voltage ratings.

Introduction to AC Drives Chapter 2 - AC Drive Fundamentals
Chapter 2 - AC Drive
Fundamentals
LEARNING OBJECTIVES
• Understand the difference between motor control using control products and AC
drives
• Understand the benefits of AC drives
• Recognize applications for AC drives
• Understand the fundamentals of how AC drives work
• Understand the basics of load considerations and drive braking

PRIMARY PURPOSES OF MOTOR CONTROL
All electric motors require a control system. That control may be as simple as an ON/OFF
switch, such as for an exhaust fan. Or, the operation may be so complex that a computer must
be used in the control system, such as in an automobile assembly plant application. Both the
exhaust fan and assembly plant electric motors are provided with start and stop control by their
control systems. But the difference between their control systems is how they provide that
control. In addition to start/stop control, a motor control system may also provide motor overload
protection as well as motor speed and torque regulation.
Square D has a very comprehensive line of control products such as motor starters, contactors,
switches, disconnects etc. These products are used in applications which include on/off controls
with jog and reverse capabilities for pumps, compressors, fans, conveyors, meat cutters, textile
looms, and wood and metalworking machines, just to name a few. Sometimes these types of
control devices (switches, contactors, etc.), are called “across-the-line” starters. This is because
full voltage and current are applied directly to the motor. An AC motor, as you learned in
Chapter 1, when switched on like this tends to run at it’s maximum rated speed and torque. For
many applications this is a perfectly acceptable situation. But there can be problems:
• The locked rotor current (also called “inrush current”) for a motor during starting can be six to
thirteen times the normal operating current. This can cause problems if the electrical
distribution system is already loaded near capacity, because excessive current draw can
cause interruption of the whole system. The excessive starting current (multiplied by the
number of motors in the facility) can cause the demand factor on the electric meter to
become very large which may double or triple the electric bill.
• Another problem created by large locked rotor currents is the wear and tear on switchgear.
When motors are allowed to draw maximum current, they can cause arcing and heat buildup
that stresses contacts and switchgear. This stress causes equipment such as disconnects,
and motor starters to wear out prematurely.
• A problem may also arise when loads are started at full torque. The starting torque of a
squirrel cage motor can be as high as 140 percent of the normal operating torque. Sudden
starting torque can damage the equipment or in the case of a conveyor, spill the materials
being conveyed.
• It may also be important to control the time it takes a motor to stop. In some applications it is
important that the load stop at exactly the time and location when the motor is de-energized.
In normal motor operation, when a motor is de-energized, the load is allowed to coast to a
stop, which means that the larger the load is, the longer the coasting time. This causes the
load to be located at random, which may be unacceptable in certain applications. For
example, if large cutting blades are turning at high speeds and are allowed to continue
rotating after power is removed, then an unsafe condition could exist.
Because of one or more of these concerns, over the years, various methods have been tried to
exert some control over motors. Some of the types of adjustable speed control that have been
used are:
• Mechanical - Mechanical methods involve using devices such as brakes, clutches, and
gearing to control motor speed. As you can imagine, these methods are not particularly
efficient.
• Hydraulic transmission control - Physically the configuration includes a torque converter.
This method is not used widely today:
 Advantages: infinite speed control and moderate cost
 Disadvantages: complex installation and high maintenance

• Electro-mechanical speed control - A combination of mechanical and electrical controls are
used. This method of control has fallen from current favor, because it is very inefficient:
 Advantages: simple and moderate cost, easy to maintain.
 Disadvantages: discrete incremental control only. Uses wound-rotor motors which are
usually non-stock, creating higher expenses and more maintenance problems.
• Eddy current - A magnetic clutch is used to adjust motor output speed in infinite increments.
It is a simple idea, and it works. However, it is very inefficient and a lot of energy is lost
through heat.
 Advantages: simple
 Disadvantages: poor efficiency and requires cooling, either by water or air.
• Electronic speed control (AC Drives) - Direct electronic controls are used most often to
control speed:
 Advantages: most efficient speed control, low maintenance, most flexible of all control
schemes.
 Disadvantages: can be more expensive at initial purchase, but saves money over time.
Energy savings and reduced wear and tear on machinery will quickly repay the initial
investment.
What Is The Difference Between a Soft Start and an AC Drive?
Square D makes different types of electronic motor control devices, two that you need to make
sure you can tell the difference between are:
• Soft start devices (i.e., Altistart 23 and 46)
• AC drives (i.e., Altivar 16, 18, 56 and 66).
A soft start device reduces the voltage, thus reducing the current, at startup to relieve the stress
on the motor and machinery. There are many, many applications where it is critical to do just
this. In addition, the soft start can allow a motor to have smooth acceleration up to 100%
operating speed and can control a motor’s smooth deceleration back down to zero as well.
An AC drive can also be a “soft start” device but it can also vary the speed and torque of the
motor according to changing machine requirements. In other words, after start up, the motor
does not have to run at 100% speed and torque but these elements can be varied to suit the
application.
The soft start device reduces the voltage thus reducing the current at startup. While an AC drive
does not reduce the startup torque. This can be a very significant factor depending upon the load
application.
In short, an AC drive can act as a soft start, but a soft start cannot act as an AC drive.
Benefits of AC Drives
The AC drive has been around only since the 1970’s. The growing popularity of AC drives is due
chiefly to their ability to provide adjustable speed control with standard NEMA B design squirrel
cage motors. Other names for AC drives are variable frequency drive (VFD) and variable speed
drive (VSD), but we’ll just call them AC drives.

Some of the reasons for the growing popularity of AC drives are:
• Energy savings, particularly for fans and pumps.
• Extended equipment life through reduced mechanical stress (belts, bearings).
• Elimination of excessive motor inrush current which in turn, extends useful motor life.
• Standard AC motors can be used. This means that off-the-shelf motors, which are easier to
repair, purchase and maintain, not to mention less expensive, can be used.
• With an AC drive, retrofits from a DC or wound-rotor motor to a NEMA B squirrel cage motor
are relatively easy.
• Solid state device which has no moving parts or contacts to wear out.
APPLICATIONS
AC drives can be applied in many of Square D’s target industries. This list gives you a good idea
of many of the types of applications and machines AC drives are used on:
Automotive Food & Beverage
APPLICATION MACHINES
Powertrain
Forming
Fabrication
Assembly
Paint Shop
Special
Machinery
Conveyors
Tool Changers
Transfer Lines
Boring/Cutting machines
Feeders
Presses
Conveyors
Welder
Shears
Parts Positioning
Hoists
Welders
Conveyors
Pumps
Ventilating Fans
Conveyors
Grinders
Deburring Equipment
Cutting Machines
Wind Tunnels
Conveyors
Filling machines
Capping machines
Labeling
Wrapping
Pumps
Conveyors
Filling, Folding, Labeling
Wrapping
Cutting Presses
Fans
Conveyors
Transporters for freezing tunnels
Screw pumps
Archimedian screw
Conveyors
Crunchers
Mixers
Dough machines
Pumps
Agitators
Pumps
Conveyors
Filling machines
Mixers
Bottling
Lines
Box & Bag
Handling
Drying
Freezing
Air Conditioning
Bakery
Confectionery
Meat
Milk & Dairy

Chemical Textile
Petroleum
Pharmacy
Fertilizers
Paint
Centrifugal Pumps
Fans
Dosing, Metering Pumps
Granulator
Mixers
Container handling
Mixers
Agitators
Packaging machines
Fans
Dosing conveyors, Pumps
Crunchers
Mixers
Packaging machines
Centrifugal Pumps
Agitators
Dosing Pumps
Crunchers
Mixers
Packaging machines
Centrifugal pumps
Agitators
Fiber
Fabrication
Fiber
Knitting
Clothing
Leather
Man Made Fibers
Bobbin winder
Texturing machines
Gear Pumps
Mixers
Extruder
Twister, Doubler
Drawing roller
Washers
Conveyers
Beam wrappers
Carding machines
Presser frames
Knitters
Circular rib knitters
Weaver’s loom
Dyers
Picking machines
Flocking machines
Printing machines
Scrapers
Bag handling machines
Screw Pumps
Archimedian screws
Sewing machines
Cutting machines
Conveyors
Washing machines
Dry cleaning
Ironer
Special machines
Transporters
Handling machines
Natural Fibers

Paper Wood
Paper
Mills
Semi-Finished
Product
Printing
Feeders
Crushers
Centrifugal Pumps
Dryers
Winding/Unwinding
Rollers
Coating machines
Conveyors
Cutting machines
Unwinding machines
Glue pumps
Packaging machines
Conveyors
Cutting machines
Ink pumps
Conveyors
Printing presses
Assembling machine
Folders
Packaging machines
Raw &Finished
Lumber
Furniture
Plywood
Saws
Ventilating Fans
Pumps
Chip Conveyors
Transfer cars
Grinders
Saws
Conveyors
Ventilating Fans
Pumps
Washers
Oven Conveyors
Material Conveyors
Metallurgy
Raw Product
Oversized
Material
Semi-Finished
Product
Finished
Product
Injectors
Crushers
Conveyors
Pumps
Fans
Wire Drawing machines
Conveyors
Steel Rolling machines
Wire Drawing machines
Press, Cutting presses
Plastic covering machines
Metal finishing treatment
Stitch seam welding machine
AC DRIVE THEORY
How Do AC Drives Work?
As you learned in Chapter 1, AC motor speed is controlled by frequency. An AC drive is a
device for controlling the speed of an AC motor by controlling the frequency of the
voltage supplied to the motor. It does this by first converting 3 phase 60 Hz AC power to DC
power. Then, by various switching mechanisms, it inverts this DC power into a pseudo sine wave
3 phase adjustable frequency alternating current for the connected motor. Because of this, some
people call AC drives “inverters,” although this is technically incorrect.

The frequency coming in to the converter has a fixed frequency of 60 Hz. However, the
adjustable frequency coming out of the inverter and going to the motor can be varied to suit the
application.
There are two general types of solid state frequency control systems available: six step and
pulse width modulated (PWM) control. All of Square D AC drives use the pulse width modulation
(PWM) method of frequency control, and that is the one we will concentrate on here.
Let’s look at how an AC drive functions in a little more detail. The two main sections of a PWM
drive are the converter and the inverter.
Three phase 60 Hz AC power is coming into the converter. The converter typically uses a
rectifier (which is a solid state device that changes AC to DC) to change the incoming 60 Hz AC
into a rectified DC voltage.
t
V
Rectifier
V
t
AC Line Voltage
(non-rectified)
DC Voltage
(rectified)
The DC voltage coming out of the converter is rather rough. Different types of filtering can be
used to smooth out the rectified DC so that it is of a more or less constant voltage value. This
filtering takes place between the converter and inverter stages. This “smoothed” DC is then sent
on to the inverter.
V
t
Inverter
DC Voltage
(non-inverted)
AC Voltage
(inverted)
V
t
The inverter section produces an AC output which is fed to the motor. Positive and negative
switching occurs within the Inverter which produces groups of voltage pulses. The output
frequency of an PWM drive is controlled by applying positive pulses in one half cycle, and
negative pulses in the next half cycle. The pulses within each group have varying widths that
Motor Leads
Converter Inverter
DC BusAC Lines
Constant
Frequency
Adjustable
Frequency
+
-

correspond to voltage values. Notice on the output side of the inverter that the narrow voltage
pulses represent the lower voltage values on the sine wave and that the wider voltage pulses
represent higher voltage sine wave values. The varying of the pulse widths gives this method its
name of Pulse Width Modulation (PWM).
This diagram is only showing 6 pulses per half cycle. For each specific frequency, there is an
optimum number of pulses and pulse widths that will closely simulate a pure sine wave.
Volts per Hertz Ratio
When current is applied to an induction motor it generates magnetic flux in its rotating field and
torque is produced. This magnetic flux must remain constant in order to produce full-load torque.
This is most important when running a motor at less than full speed. And since AC drives are
used to provide slower running speeds, there must be a means of maintaining a constant
magnetic flux in the motor. This method of magnetic flux control is called the volts-per-hertz
ratio. With this method, the frequency and voltage must increase in the same proportion to
maintain good torque production at the motor.
For example, if the frequency is 60 Hz and the voltage is 460 V, then the volts per Hertz ratio
(460 divided by 60) would be 7.6 V/Hz. So, at half speed on a 460 V supplied system, the
frequency would be 30 Hertz and the voltage applied to the motor would be 230 V and the ratio
would still be maintained at 7.6 V/Hz.
This ratio pattern saves energy going to the motor, but it is also very critical to performance. The
variable-frequency drive tries to maintain this ratio because if the ratio increases or decreases as
motor speed changes, motor current can become unstable and torque can diminish. On the other
hand, excessive current could damage or destroy the motor.
In a PWM drive the voltage change required to maintain a constant Volts-per-Hertz ratio as the
frequency is changed is controlled by increasing or decreasing the widths of the pulses created
by the inverter. And, a PWM drive can develop rated torque in the range of about 0.5 Hz and up.
Multiple motors can be operated within the amperage rating of the drive (All motors will operate
at the same frequency). This can be an advantage because all of the motors will change speed
together and the control will be greater.
460 V
60 Hz0 Hertz
Volts
230 V
30 Hz

LOAD CONSIDERATIONS
The type of load that a motor drives is one of the most important application considerations when
applying any type of AC drive. For some types of loads, the application considerations may be
minimal. For other types of loads, extensive review may be required. Generally, loads can be
grouped into three different categories:
• Constant Torque Loads - conveyors, hoists, drill presses, extruders, positive displacement
pumps (torque of these pumps may be reduced at low speeds).
• Variable Torque Loads - fans, blower, propellers, centrifugal pumps.
• Constant Horsepower Loads - grinders, turret lathes, coil winders.
Constant Torque Loads
Constant torque loads are where applications call for the same amount of driving torque
throughout the entire operating speed range. In other words, as the speed changes the load
torque remains the same.
Constant 100% Torque
At 50% Speed:
•Torque = 100% of
full load torque
•HP = 50% of
full speed BHP
0 50 100
50
100
Percent Speed
PercentTorqueandHorsepower
Torque
H
orsepow
er
The chart shows speed on the bottom and torque on the left. The torque remains the same as
the speed changes. Horsepower is effected, and varies proportionately with speed. Constant
torque applications include everything that are not variable torque applications. In fact, almost
everything but centrifugal fans and pumps are constant torque.
Variable Torque Loads
As was just mentioned, there are only two kinds of variable torque loads: centrifugal pumps and
fans. With a variable torque load, the loading is a function of the speed. Variable torque loads
generally require low torque at low speeds and higher torque at higher speeds.
Fans and pumps are designed to make air or water flow. As the rate of flow increases, the water
or air has a greater change in speed put into it by the fan or pump, increasing its inertia. In

addition to the inertia change, increased flow means increased friction from the pipes or ducts.
An increase in friction requires more force (or torque) to make the air or water flow at that rate.
The effects that reduced speed control has on a variable torque fan or pump are summarized by
a set of rules known as the Affinity Laws. The basic interpretation of these laws is quite simple:
1. Flow produced by the device is proportional to the motor speed.
2. Pressure produced by the device is proportional to the motor speed squared.
3. Horsepower required by the device is proportional to the motor speed cubed.
100% Load at
100% Speed
0 50 100
100
Percent Speed
PercentTorqueandHorsepower
Torque
Horsepower
12.5
25
At 50% Speed:
•Torque = 25% of
full load torque
• HP = 12.5% of
full speed brake
horsepower (BHP)
The cube law (third item) load is at the heart of energy savings. The change in speed is equal to
the horsepower cubed. For example, you might expect a 50% change in speed would produce a
50% change in volume, and would require 50% of the horsepower. Luckily for us, this 50%
change in speed must be cubed, representing only 12.5% of the horsepower required to run it at
100% speed. The reduction of horsepower means that it costs less to run the motor. When these
savings are applied over yearly hours of operation, significant savings accumulate.
This table will help show these relationships:
% Speed % Torque % HP
100 100 100
90 81 72.9
80 64 51.2
70 49 34.3
60 36 21.6
50 25 12.5

Constant Horsepower
A constant horsepower load is when the motor torque required is above the motor’s base speed
(60 Hz). With a constant horsepower type of load, the torque loading is a function of the
changing physical dimensions of the load. These types of applications would include grinders,
turret lathes and winding reels. Constant horsepower loads require high torque at low
speeds and low torque at high speed. While the torque and speed changes the horsepower
remains constant.
For example, an empty reel winding a coil will require the least amount of torque, initially, and
will be accelerated to the highest speed. As the coil builds up on the reel, the torque required will
increase and the speed will be decreased.
BRAKING
An electric motor moves its load and demands whatever amount of power is required to get the
load moving and keep it moving. Once the load is in motion it has inertia and will tend to want to
stay in motion. So, while we must add energy to get the load into motion, we must somehow
remove energy to stop it.
Some large motor loads develop high inertial forces when they are operating at high speed. If
voltage is simply disconnected from the motor, the load may coast for several minutes before
the shaft comes to a full stop. This is true in applications such as those involving large saw
blades and grinding wheels. It’s important for safety reasons to bring these loads to a smooth
stop quickly.
In other load applications, such as elevators and cranes, the location where the load stops is as
important as moving the load. This means that the motor shaft must stop moving at a precise
time to place the load at its proper location.
There are several different types of braking techniques used, however we are only going to
mention the two types used on Square D drives: DC braking and Dynamic braking.
In DC braking, DC current is applied to the stationary field of an AC motor when the stop button
is depressed. Since the field is fixed and it replaces the rotating stator field, the rotor is quickly
stopped by the alignment of the unlike magnetic fields between the rotating and stationary
windings. The attraction between the rotating and stationary fields is so strong that the rotor is
stopped quickly. This method of stopping is only effective at 10 Hz and below. The energy
% HP and
Torque
% Speed
100 %
100 %
80 %
60 %
40 %
20 %
200 %
Horsepower
Torque
0

created with this type of braking will be dissipated in the rotor and care needs to be used when
applying this type of braking. Square D uses this method to a limited degree.
Dynamic braking is used by Square D in its Altivar 66 drives. When the voltage is removed
from a motor and the inertia of the load continues on in motion, the motor is being driven by the
load until it coasts to a stop. Since the rotor will continue to spin, it will produce voltage and
current in a manner similar to a generator. This generator action can be used to bring the rotor to
a quick stop by sending the generated energy out to a resistor. There the energy is dissipated as
heat through the resistor. The resistor will cause the rotor to generate very high levels of current,
which produces magnetic forces on the shaft and causes it to stop quickly.

True or False:
1. _____ “Across the Line” starters (and contactors) control both AC motor torque and
speed.
2. _____ DC braking is when DC current is applied to the stator of an AC motor when the
stop button is pressed.
3. _____ One advantage of AC drives is that less expensive, off-the-shelf AC motors
(i.e., squirrel cage) that are easier to purchase and maintain can be used for
multispeed applications.
4. _____ Variable torque loads generally require low torque at low speeds and higher
torque at higher speeds.
5. _____ Examples of constant horsepower loads would be: fans, blowers, and
centrifugal pumps.
6. _____ If the Volts per Hertz Ratio is not maintained motor current could become unstable
and torque could diminish.
7. Match the parts of an AC drive:
_____ Inverter A. This section smoothes rectified DC before it goes
_____ DC bus filtering B. This section changes DC into an adjustable frequency
synthetic AC.
_____ Converter C. This section changes 60 Hz AC power into DC.

SELF CHECK ANSWERS
True or False:
1. F “Across the Line” starters (and contactors) control both AC motor torque and
speed.
2. T DC braking is when DC current is applied to the stator of an AC motor when the
stop button is pressed.
3. T One advantage of AC drives is that less expensive, off-the-shelf AC motors
(i.e., squirrel cage) that are easier to purchase and maintain can be used for
multispeed applications.
4. T Variable torque loads generally require low torque at low speeds and higher
torque at higher speeds.
5. F Examples of constant horsepower loads would be: fans, blowers, and
centrifugal pumps.
6. T If the Volts per Hertz Ratio is not maintained motor current could become unstable
and torque could diminish.
7. Match the parts of an AC drive:
B Inverter A. This section smoothes rectified DC before it goes
A DC bus filtering B. This section changes DC into an adjustable frequency
synthetic AC.
C Converter C. This section changes 60 Hz AC power into DC.

Introduction to AC Drives Chapter 3 - Square D AC Drive Products
0
Chapter 3 - Square D
AC Drive Products
LEARNING OBJECTIVES
The participant will be able to identify the basic features of the following drives:
• OMEGAPAK®
8803 and 8804
• ALTIVAR®
16, 18, 56, and 66
Note: The intent of this chapter is to give you an introduction to the terminology used
when speaking about a drive’s features with your customer.

OMEGAPAKS 8803®®®®
and 8804 OVERVIEW
Before starting to learn about Square D’s newest AC drive products let’s take a few moments to
review what Square D AC drives are already in the market place. One drive type that your
customers may inquire about is the Square D OMEGAPAK family (8803 or the 8804). The
OMEGAPAK family of AC drives are designed to provide reliable, cost-effective speed control
for AC induction motors. OMEGAPAK drives run both constant and variable torque applications.
They are available in a variety of enclosure styles, and the OMEGAPAK family offers many
optional features. Whatever the variable speed control needs  from pump and fan applications
to machine and process control functions  the OMEGAPAK has been available for dependable
control, effective motor protection and substantial energy savings.
Using pulse width modulated (PWM) inverter technology, OMEGAPAK drives minimize output
current harmonic distortion, improve starting torque and provide smooth low-speed operation.
This simple design uses a diode bridge rectifier to enhance reliability, reduce AC line noise and
provide high displacement power factor. OMEGAPAK drives effectively replace throttling valve,
dampers and other mechanical means of speed and flow control, adding control capabilities
while, at the same time, reducing energy costs. Due to new product development the
OMEGAPAK 8803 and 8804 are classified as older technology drives, therefore, Square D has
placed these drives on the reduced availability list. That means that the OMEGAPAK drives can
only be ordered as replacements for existing OMEGAPAK applications. For all new drive
applications the ALTIVAR family should be recommended. This section has been included so
you will have a basic knowledge about the drive if a user should call and request an
OMEGAPAK drive.
The complete family of OMEGAPAK drives includes:
• Type PT - a constant/variable torque controller for low horsepower (1-10 HP)
applications;
• Type VT - a variable torque drive suitable for pump, fan and blower control;
• Type CT - a constant torque drive featuring unique connectivity options, making
it particularly useful in remote operation, integrated automation and machine
 and process  control systems.
Let’s take a look at the features of two of the OMEGAPAK drives, the OMEGAPAK 8804 and the
OMEGAPAK 8803.

OMEGAPAK 8804®®®®
OMEGAPAK Type PT
OMEGAPAK Class 8804 Type PT family of AC drives offers reliable, cost-effective speed
control for low horsepower, standard three-phase AC induction motors. Compact and flexible in
design, the PT provides controlled acceleration and deceleration for a variety of applications.
Features include:
• Fuseless output short circuit and ground fault protection
• UL listed fault withstand rating of 65,000 RMS symmetrical construction
• Extensive options are offered for customizing PT drives:
− Pilot device options
− Option boards
− Dynamic braking
− Power options
OMEGAPAK Type VT
The OMEGAPAK VT drive was engineered specifically for variable torque applications such as
centrifugal pumps and fans. OMEGAPAK Type VT drives require less electrical power than
mechanical methods of liquid or air flow control to produce a given rate of flow. Highly efficient in
operating standard AC squirrel cage motors, VT drives produce significant energy savings
combined with top-notch performance and reliability. The OMEGAPAK VT family provides:
• Fuseless output and ground fault protection
• UL listed fault withstand rating of 65,000 RMS symmetrical amperes
• Solid state overload protection
• Analog follower input
• Versatile construction with open, wall-mounted and motor control center style enclosures are
available
• Extensive options for customizing VT drives

OMEGAPAK Type CT
The OMEGAPAK CT drive was engineered specifically for constant torque applications such as
process control and machine applications, for example. The sine−coded PWM output provides
improved starting torque and reduces motor heating effects. The diode bridge provides a high
displacement power factor and reduces AC line noise. Standard and optional features provide
the flexibility necessary for effective variable speed applications. The OMEGAPAK CT family
provides:
• Fuseless output and ground fault protection
• UL listed fault withstand rating of 65,000 RMS symmetrical amperes
• High starting torque
• Solid state overload protection
• Drive connectivity through serial communications with SY/MAX®
programmable controllers
for motion control applications in sophisticated automation systems.
Additional Features
• User-selectable process control functions
• User-programmable and configurable input ports
• Isolated RS-422 serial communications
OMEGAPAK 8803
OMEGAPAK Class 8803 Standard Enclosed Drives provide customers with a simple, reliable
and safe method of using and installing OMEGAPAK Type P, Constant, and Variable Torque AC
Drives. The OMEGAPAK 8803 drives have the following standard and optional features:

Standard Features:
• Manufactured in compliance with ISO 9002
• Three power options for enclosed drives
• Three control options for enclosed drives
• Options for Standard Enclosed Drives are arranged to provide ease of access and wire
termination
• NEMA Type 12 enclosure
• Panel mounted line fuses provided as standard to protect drive regardless of disconnect
means
• Internal Stirring Fan - eliminates isolated heat spots and ensure maximum ambient
temperature exposure
• 120 Volt User Control Power
• User mounting space - for three 6.75 inch DIN rails to accommodate user mounted devices
Optional Features:
• Choice of Door-Interlocked Disconnect Means:
− Circuit Breaker
− Disconnect switch (not fused)
• Input Contactor - provides automatic AC drive isolation from the line in the event of drive
faults and timed isolation upon command to stop
• Bypass Contactor - drive isolation and manual bypass provide emergency full speed
operation in the event of drive fault
• Choice of Operator Control - 2 - wire maintained control with Forward/Reverse selector
switch
Available Field Installed Options
• Do-it-yourself kits available for NEMA Type 12 enclosures, control, power and disconnect
options
• Dynamic Braking
• Serial Communications
• Commissioning Terminal
• +/- 10 v Speed Reference Interface
• 200 Hertz Software

ALTIVAR OVERVIEW
Now that you have reviewed what Square D AC drives are in the marketplace, let’s continue on
and learn about Square D’s newest AC drive family, the ALTIVAR drives. The complete
ALTIVAR drive family ( ALTIVAR 16, 18, 56, and 66) provides compact size and full-featured
performance for a wide range of applications and motor sizes. Manufactured to ISO 9000 series
standards, ALTIVAR drives meet UL, CSA, IEC and VDE standards. Because the drives were
developed as a global product, the ALTIVAR drive family can meet your customer’s needs
locally as well as worldwide. The ALTIVAR family is a growing line of advanced drives from
Square D.
ALTIVAR®®®®
16 FEATURES
With the ALTIVAR 16 your customers no longer have to sacrifice full-featured AC drive
capability for compact size. Now, you can give your customers both with the remarkably compact
ALTIVAR 16 AC drive. Because it is simple and modular, the ALTIVAR 16 is a viable

replacement for other variable speed motor controls. With a higher degree of versatility and
control than conventional starters, the ALTIVAR 16 drive is a very cost-effective yet advanced
starting option for controlling motors of 5 HP and less. The basic unit requires no programming
 wire in, wire out, and its ready to run. However, the ALTIVAR 16 can be custom programmed
with a plug-in keypad, personal computer or programmable controller. You can add even more
functionality with a plug-in option card pre-configured for your customer’s particular application.
Because all of this performance comes in a very compact package, the ALTIVAR 16 drive
makes it easy to retrofit constant speed motor controls or to substantially reduce panel size.
Features include:
• Rated power size ranges from 1/2 to 3 HP (200-240V AC) and 1 to 5 HP (400-460V AC)
• Protection against short circuits:
− Between output phases
− Between output phase and ground
− In internal power supplies
• Overload and overtemperature protection
• Overvoltage and undervoltage protection
• Protection against phase loss (ATV16U-N4 only)
• NEMA 1, IP30
• UL, CSA, IEC, VDE
• Factory-configured option cards for specific industry segments
− General use / material handling
− Centrifugal pumps, fans
− Textile, wood process, high speed motors
The features for each industry include:
• General use / material handling
− S ramp - Used for “S” Curve Acceleration and Deceleration smoothness and reduces
consequent shock as the drive controller accelerates or decelerates from
current speed to setpoint speed.
− Fault reset - Allows drive to reset the resettable faults when in Terminal Command
mode.
− Jog
− Preset speeds
− Three stopping methods
• Freewheel - Allows the motor and load to coast to a stop due to normal design of
the system
• Ramp to Stop - Allows the motor and load to ramp to a complete stop within a
settable amount of time
• Brake control - Dynamic braking or DC injection braking
• Centrifugal pumps, fans
− Variable torque volts/Hz ratio
− 10 Khz switching frequency - Helps reduce audible motor noise
− Automatic restart - When a fault occurs the drive will attempt to restart for a maximum of
5 times.
− Jump frequencies - Reduces mechanical resonance in a fan or pump.
− Controlled stop on loss of input power

− Automatic/manual switching input - Switches the speed reference to the drive from auto
to manual.
• Textile, wood process, high speed motors
− Inhibited slip compensation
− Jog
− Freewheel stop
− Switch to ramp 2 - Allows different acceleration rates based on either a logic input or a
frequency level
− Automatic catching a spinning load - Allows drive to operate into a spinning motor.
− Frequency range extended to 400 hz
ALTIVAR®®®®
66 FEATURES
The AC drives market is now opening up into areas previously dominated by standard motor
control applications such as fans, pumps and conveyors. The ALTIVAR 66 product range covers
the growing need of variable speed drives, for asynchronous motors from 3 to 350 HP (CT). The
ALTIVAR 66 drive is in synergy with the ALTIVAR 16 drive to cover the market for variable
speed drive applications. The range of the ALTIVAR 66 is comprised of the following parts:
• Basic product
• Additions that support and enhance the functionality of the base product and
• Standard enclosure packages
Due to the available horsepower ranges of the ALTIVAR 66 and 56 drives, maintenance and
service issues are greatly simplified. Since the horsepower range goes from 3 to 350 HP (CT)
users and distributors are able to reduce their drive inventory. There are 3 centers of production
and distribution for the ALTIVAR family:
• Europe
• Southeast Asia
• United States (Raleigh)
When the ALTIVAR 66 arrives at your location or the customer’s site the drive is set up for
operation with average performance and no factory made adjustments. The following are the
factory settings.

Factory Settings:
• Constant torque
• Two-wire control
• Rated motor frequency according to supply frequency
• Motor voltage:
− 50 Hz detected sets drive up for 400V
− 60 Hz detected sets drive up for 460V
• Adjustments:
− Acceleration ---> 3s
− Deceleration ---> 3s
− Low Speed ---> 0 Hz
− High Speed ---> 50 or 60 Hz depending on supply frequency
• Functions:
− Slip compensation - adjusting the volts per hertz ratio in the drive
− DC injection for frequency < 0.1 Hz (70% of current for a half of second)
Sensorless Vector Control
Normally when an AC drive provides vector control, the drive requires a feedback device such
as a tachometer, resolver, or encoder. These feedback devices provide the motor’s shaft speed
and position feedback to the drive. The AC drive in turn, uses the feedback along with a
mathematical motor model, and current vectors to determine and control the actual speed,
torque, and power produced by the motor on a continuous basis.
As technology advanced, several methods of controlling torque at low frequencies emerged
without a need for the feedback devices. This method of control is called Sensorless Vector
Control. Sensorless Vector Control is a method used by the ALTIVAR 66 AC drive to produce a
constant torque at the load without having the motor provide any feedback to the AC drive. To
accomplish this the AC drive must increase the control voltage to the motor along with the
frequency to produce a constant stator magnetic flux field in the motor. The ALTIVAR 66 drive
accomplishes constant torque by using a mathematical motor model. By automatically
measuring the motor’s stator resistance and the mutual inductance of the motor and with the
drive’s onboard database of motor models, the drive’s micro-processor is able to refine the
mathematical model on the fly and accurately control the motor’s constant torque without the
need of motor feedback devices.
Reduction of Motor Noise
Reduction of motor noise is accomplished in the ALTIVAR 66 by the following methods:
• Random frequency generation
• Combination of fixed switching frequency and random frequency
• Reduction of unpleasant switching frequency noise (less high-pitch noise)
Motor Noise Comparison Chart
The graph below shows the relationship between the drive’s switching frequency (Hz) and the
motor’s noise level (dBA) when connected directly across a 60 Hz line. Notice by switching the

carrier frequency at different frequencies (4kHz, 10kHz, etc.) the actual noise level produced by
the motor can be reduced. This can be demonstrated by comparing line number 2 at different
frequencies (10, 20, etc. ) on the graph to the dot, number 3, which is the normal amount of
noise a motor generates when across a 60 Hz line.
20
40
60
80
dBA
0
0 10 20 30 40 50 60
Hz
4
1
2
3
1 - switching at 4 kHz with random carrier
2 - switching at 10 kHz with random carrier
3 - motor directly connected to AC supply
4 - 8803 P
Drive Interfaces
The ALTIVAR 66 drive interfaces are broken down into the following areas.
• Operator Interfaces
− Start-Stop
− Other Controls
− Programmable Controllers
− Building Management
− Supervisory Control
• Input/Output Interfaces − Examples of I/O interfaces are indicators, metering, etc.

Base product Input/Output assignments for the Analog, Digital, and Relay terminals
The following legend and table shows what the default drive assignments are and what they can
be reassigned to:
Legend:
AI = Analog Input
AO = Analog Output
LI = Logic Input
LO = Logic Output
R = Relay
Default assignment Reassignment I/O
Speed reference Current limit, motor voltage AI1
Speed reference Current limit, motor voltage AI2
Output frequency See configuration manual AO1
Output current See configuration manual AO2
Run Permissive (2-wire) NO LI1
Run Forward (2-wire) NO LI2
Run Reverse (2-wire) See configuration manual LI3
Jog See configuration manual LI4
Speed reached See configuration manual LO1
Current limit reached See configuration manual LO2
Speed controller fault NO R1
Speed controller operating See configuration manual R2
Protection
AC Supply Protection
• Overvoltage: +10% at 240V, +15% at 460 V
• Undervoltage: -10% at 208V, -15% at 400 V
− Time of a fault is less than 10ms the drive will Reset (t < 10ms - Reset)
− If time is greater than 10ms but less than 200ms - Reset current and Reset the ramp
or Reset current without resetting the ramp (restart with automatic catching of
spinning load without time constant, by measuring generator E)
− Time greater than 200ms - Activate fault relay
• Phase failure
− Time greater than 1 second (t > 1s) - Activation of fault relay with choice of stop
mode: freewheel, ramp, fast.
• AC supply interference
− Interference suppression: provided in the basic product (electromagnetic
compatibility, IEC-VDE standards)
− high energy overvoltage: additional inductors
• Braking in the event of supply failure: switching mode supply
− programmable function

Other ALTIVAR 66 Protection
• Short circuits on +/- 10V, +/- 24 V supplies: electronic
• Short circuits between phases: Frame 1, 2 - Intelligent Power Module (IPM). Frame 3 to 7 -
desaturation measurement
• Short circuits between phase and earth: Frame 1, 2 - IPM. Frame 3 to 7 − current sensor
• Controller overheating: fault - Frame 1, 2 - IPM. Frame 3 to 7 - NTC (negative temperature
coefficient) probe. Early warning - ventilation fault. Frame 3 to 7 - NTC probe.
• Detection for presence of motor current reading - Measurement of 2 phases
• Current limit: 2 times In (nominal current) rms for 200 ms - on starting and/or on a load
surge
• DC bus overvoltage: 850 V for the 400/460 V controller
• DC bus undervoltage: 480 V for the 400/460 V controller
• Monitoring of charging circuit for filtering capacitors
• Mechanical locating devices for connectors
Motor Protection
• Adjustable current limit: 45 to 150% of the controller rated current
• Motor thermal overload saved on loss of supply
− Integrates time constants of various motors (overheating and cooling)
− Self-ventilated motor
− Motor ventilated motor
− Client motor, derated motor special profile to be programmed
• motor rated current
• minimum speed at full load
• maximum motor torque at zero speed
• Detection of motor phase loss (yes-no)
• Recognition of external client fault
• Adjustment of the V/Hz ratio at the motor load
• Adjustment of the frequency in the event of motor overload
Protection of the Driven Mechanism
• Limitation of excessive torque
• 4 quadrant torque regulation
• Limitation of speed surges
• Machine overloads
• Inhibition of critical operating speeds
• Inhibition of surges when restarting following a supply break
• Machine safety
• Protection of the process

Options:
I/O Extension Modules (B1, B2)
When a B1 or B2 I/O extension card is installed the controller these additional features become
available:
• Additional logic and analog functions (see table below)
• Automatic I/O configuration of I/O extension module when module is added to the ALTIVAR
drive
• Communications (see Communications next page.)
B1 and B2 I/O Extension Cards have the following features:
F1 F2 F3
0 RUN STOP
ENT
ESC
1 2 3
4 5 6
7 8 9
ALTIVAR 66
Logic
inputs
Logic
outputs
Analog
inputs
Analog
outputs
B1
B2
4 - 24VDC
8 - 115VAC
2
2 1
12
2
Communication
The communication can be connected through either one of the following extension cards:
• B1 extension module
• B2 extension module
• Communication card carrier module
With the card installed the ALTIVAR can communicate to the following industrial protocols:
• Uni-Telway
• Modbus RTU/ASCII
• Modbus+

Dynamic Braking
A braking system is required when the natural deceleration time of the motor and attached
equipment is longer than the deceleration ramp. Dynamic Braking is often the best choice when
decelerating from high speeds. For an explanation of Dynamic Braking, refer back to Chapter 2
“Braking.”
Major Components for Dynamic Braking
• A power semi-conductor to switch resistor circuit in and out.
• Separately mounted braking resistor
ALTIVAR®®®®
56 FEATURES FOR FAN AND PUMP APPLICATIONS
Design Philosophy
The ALTIVAR 56 was designed mainly with the construction market in mind. The ALTIVAR 56 is
a Variable Torque Fan and Pump Drive available in ratings from 1 - 100 HP 460 V and 1 - 50 HP
230/208 V. These products can be configured to operate in a “Low Noise” mode using a higher
switching frequency by derating the products. Low Noise ratings are available from 1 - 75 HP
460 V and 1 - 40 HP 230/208 V.
The ALTIVAR 56 drive is based upon the popular ATV66 drive and uses many of the same spare
parts, hardware and options. As an application specific product, much of the complexity of the
ALTIVAR 66 has been eliminated by optimizing the performance for fan and pump applications.
The ALTIVAR 56 is also available as a UL listed Class 8839 combination package mounted on a
back panel with a NEMA 1 contactor “BELE” box beneath the drive. The ALTIVAR 56
combination drives are available in 3 “Package” designs:
ATV56 Combo Package (W) - includes 200kAIC rated drive input fuses, MagGuard circuit
breaker with provisions for lock out and H-O-A selector switch with manual speed potentiometer.
BELE Box Features
Bypass Package (Y) - includes drive isolation contactor, IEC motor stator with class 10
overload, 200 kAIC rated drive input fuses, control transformer, MagGuard circuit breaker with
provision for lock out. AFC-Off-Byp, and H-O-A selector switch with manual speed
potentiometer.
Remote Starter Bypass Package (Z) - includes drive isolation contactor, IEC motor stator with
class 10 overload, 200 kAIC rated drive input fuses, control transformer, MagGuard circuit
breaker with provision for lock out. AFC-Off-Byp, and H-O-A selector switch with manual
potentiometer.
The features of the ALTIVAR 56 are as follows:
• Variable torque for fan & pump applications
• Easy setup for quick installation
• Limited “advanced” features
 Simplified menu system
 Limits programming decisions customer has to make
 Simplified documentation required to support software

Language
The ALTIVAR can communicate in one of the following languages:
• English
• Spanish
• French
Design Notables
• Logic input defaults:
− LI3 - AUTO/MANUAL
− LI4 - AUTO RUN
• When using Class 8839 ATV56 DO NOT turn on BYPASS function
− Class 8839 uses external relays for bypass sequencing
• Even though Run Reverse can not be configured as a logic input, the controller can still
reverse phase rotation
− If the controller is configured for AI1/AI2 summing and AI2 is multiplied by (-1) and the
result is a negative value, the controller will run in reverse

ALTIVAR®®®®
18 FEATURES
Overview
The ALTIVAR 18 is a simple and compact OEM drive. The ALTIVAR 18 drive is similar to the
ATV 16 but is non-modular and has an extended horsepower range. The drive is capable of
controlling motors of 20 HP and less. With built-in filters, the ALTIVAR 18 meets CE standards.
With the cost effectiveness and advanced technology of the drive it can be used in a wide
variety of applications. Typical examples are:
• Pumps / Compressors
• Fans
• Horizontal handling
• Packing / Packaging
• Special machines:
− Woodworking
− Textile
− Mixers
− Blenders
Features:
Choice of type of Volts/Hz control
When setting the Volts/Hz control in the ALTIVAR’s menu, you will choose one of the following
parameters:
• P - will set the drive to V/F variable torque for Pumps / Compressors (Centrifugal and
metering pumps, screw compressors)
• n - will set the drive to vector control for Horizontal handling, Packing / Packaging,
Special machines
• nld - will set the drive to energy saving for Fans
• Switching frequency
• Auto DC injection at standstill f<0.5Hz - Horizontal handling, Packing / Packaging, Special
machines
Drive Customization
• Autotuning - Horizontal handling, Packing / Packaging, Special machines
• Auto-adaptation of the deceleration ramp - Pumps / Compressors, Fans, Horizontal handling,
Packing / Packaging, Special machines
• Auto speed retrieval (catch on the fly) - Pumps / Compressors, Fans, Horizontal handling,
Packing / Packaging, Special machines
• Automatic restart - Pumps / Compressors, Fans
• Controlled stopping on main failure - Horizontal handling and Special machines
Application functions
• Skip frequencies - Fans, Mixers, and Blenders
• Low-speed operating time limit - Pumps / Compressors

Application Customization
• Analog inputs
− Summing - Horizontal handling, Packing / Packaging, and Special machines
− PI regulator - Pumps / Compressors, Fans
Logic Inputs
• 2 directions of operation - Horizontal handling, Packing / Packaging, and Special machines
• DC injection - Fans, Mixers, and Blenders
• Fast stop - Horizontal handling, Packing / Packaging, and Special machines
• Jog - Horizontal handling, Packing / Packaging, and Special machines
• Preset speeds - Fans, Horizontal handling, Packing / Packaging, and Special machines
Logic Inputs
• Speed reference reached - Pumps / Compressors, Fans, Horizontal handling
• Frequency threshold reached - Pumps / Compressors, Packing / Packaging, Mixers, and
Blenders
Range
• 17 ratings in 5 sizes - Built-in EMC filters through the range
• .5 HP through 20 HP
• IEC, UL, CSA, EN, CE mark
Equivalent ATV 16 / ATV 18
ATV 16
• Rated controller current = 1.1 rated motor current
• Thermal current ratting (Ith) setting:
− 0.45 to 1.05 In controller
− 0.45 X 1.1 In motor = 0.5 In motor
− 1.05 X 1.1 In motor = 1.15 In motor
ATV 18
• Rated controller current = Rated motor current
• Thermal current rating (Ith) setting: 0.5 to 1.15 In motor
Performance:
• Drive quality
 Smooth motor rotation without jolts at low speed (f ≤ 5 Hz)
 Stable motor current, irrespective of the motor’s load state and speed (little pulsating
torque)

• Speed
 Frequency range: 0.5 to 320 Hz
 Speed range: constant torque 1:50 (1 to 50 Hz)
• Reference
 Sampling time 5 ms
 Frequency resolution with analogue reference (10 bits, 1024 points)
» 0.1 Hz to 100 Hz
» 0.3 Hz to 320 Hz
• Frequency accuracy with analog reference: ± 0.3% of maximum set frequency

Use the information presented in this chapter to answer the following:
1. Due to new product development OMEGAPAK (8803 and 8804) drives are limited in their
availability. _____ (T or F)
2. When the ALTIVAR 66 arrives at your location the drive is set up for: (Circle the correct
answer.)
A. operation with average performance and no factory made adjustments.
B. operation with average performance and some factory made adjustments.
C. operation with optimized performance and no factory made adjustments.
D. operation with optimized performance and all factory made adjustments.
3. The ALTIVAR 66 helps reduce motor noise by:
A. Random frequency generation, fixed switching frequency, and a reduction of unpleasant
fixed switching frequency noise (less high-pitch noise)
B. Constant frequency generation, fixed switching frequency, and a reduction of unpleasant
switching frequency (less high-pitch noise)
C. Random frequency generation, combination of fixed switching frequency and random
frequency, and a reduction of unpleasant switching frequency (less high-pitch noise)
4. The software that runs the ALTIVAR 56 was designed for the ________ market.
A. Industrial
B. Construction
C. Residential
D. All of the above
5. The major differences between the ALTIVAR 66 and the ALTIVAR 56 are:
A. Variable torque for fan & pump applications, easy setup for quick installation, removal of
“advance” features, removal of constant torque, removal of communications.
B. Constant torque for fan & pump applications, easy setup for quick installation, additional
“advance” features, additional communications.
C. There are no major differences between the ALTIVAR 66 and the ALTIVAR 56

SELF CHECK ANSWERS
1. Due to new product development OMEGAPAK (8803 and 8804) drives are limited in their
availability. T (T or F)
2. When the ALTIVAR 66 arrives at your location the drive is set up for: (Circle the correct
answer.)
A. operation with average performance and no factory made adjustments.
B. operation with average performance and some factory made adjustments.
C. operation with optimized performance and no factory made adjustments.
D. operation with optimized performance and all factory made adjustments.
3. The ALTIVAR 66 helps reduce motor noise by:
A. Random frequency generation, fixed switching frequency, and a reduction of unpleasant
fixed switching frequency noise (less high-pitch noise)
B. Constant frequency generation, fixed switching frequency, and a reduction of unpleasant
switching frequency (less high-pitch noise)
C. Random frequency generation, combination of fixed switching frequency and
random frequency, and a reduction of unpleasant switching frequency (less high-
pitch noise)
4. The software that runs the ALTIVAR 56 was designed for the ________ market.
A. Industrial
B. Construction
C. Residential
D. All of the above
5. The major differences between the ALTIVAR 66 and the ALTIVAR 56 are:
A. Variable torque for fan & pump applications, easy setup for quick installation,
removal of “advance” features, removal of constant torque, removal of
communications.
B. Constant torque for fan & pump applications, easy setup for quick installation, additional
“advance” features, additional communications.
C. There are no major differences between the ALTIVAR 66 and the ALTIVAR 56

Introduction To AC Drives Chapter 4 - AC Drive Types
Chapter 4 - AC Drive
Types
LEARNING OBJECTIVES
• Be able to identify an open type drive
• Be able to identify an enclosed type drive
• Be able to identify a MCC type drive

DRIVE TYPE OVERVIEW
In this course, so far, you have learned about AC motor fundamentals, AC drives fundamentals,
and Square D’s AC drive products. In this chapter you will learn about the types of AC drives. AC
drives can be categorized into three types; open type, enclosed type, or Motor Control Center
(MCC). Square D’s AC drives can be utilized for all three types. Let’s explore each drive type.
OPEN TYPE DRIVES
Definition of Open Type Drive
An open type drive is where the user buys the drive as a component piece, to use as is or to be
built into their own enclosure or machine. The user installs the drive into their enclosure and
does all of the interfacing necessary for the drive to function properly in the application.
When assisting a user in selecting an open type drive it is beneficial to ask the user if the drive
will reside inside an enclosure. If the answer is yes, then you should ask for the dimensions of
the allotted drive space in the enclosure, to ensure that the drive will physically fit in the
enclosure. This practice of asking the user for the drive's space dimensions, whether the drive is
a new installation or a retrofit, will be a value added feature to your user’s satisfaction level and
save time on both sides.
It is also beneficial to ask the user how they are dissipating the heat inside their enclosure. This
way you can verify that the drive will fit correctly and operate in the environment of the user’s
enclosure. Identifying if a user has an open type drive will be covered in the section on “How To
Identify The Drive Type,” later in this chapter.
Which Square D AC Drives Can Be Used For Open Type Applications?
Of the drives covered in this course, the ALTIVAR 16, 18, and 66 can be used for open type
applications.

ENCLOSED TYPE DRIVES
Definition of Enclosed Type Drive
An enclosed type drive (Class 8839) is where the a user requests Square D to pre-engineer the
drive and enclosure. The Square D Columbia plant in South Carolina builds our enclosed type
drives. Items such as Bypass Control Schemes, Hand-Off-Auto Selector Switches, Start/Stop
pushbuttons, Jogging selectors, Speed pots, etc. can be incorporated into the drive enclosure.
Enclosed Type drives are offered in NEMA Type 1, and Type 12 enclosures. Identifying if a user
has an enclosed type drive will be covered in the section on “How To Identify The Drive Type,”
later in this chapter.
Which Square D AC Drives Can Be Used For Enclosed Type Applications?
Of the drives covered in this course, the ALTIVAR 56, and 66 can be used for enclosed type
applications. The ALTIVAR 56 is only available as an enclosed type drive.

Enclosure Power Circuits
65kA
M
Fan
FC FF
AFC
Once the drive has been selected for the application, the next step is to choose what power
circuit configuration will be mounted into the enclosure. There are several to choose from
depending on the application. When choosing a power circuit there are many factors to take into
consideration:
• The National Electric Code (NEC)
• Plant practices and local building codes
• Selection for minimum voltage drops
• Methods to reduce or eliminate magnetic radiation or electrical noise and
• The actual current carrying capacity of the cables based on the drive size and loading.
The power circuit also serves as a reference point when it comes to wiring electrical equipment
and other components needed for drive technology. When working with enclosed drive
enclosures, the letters A through K are used in the enclosure’s configuration number to
differentiate the power circuits required by the user for their application. For a better
understanding of how each power circuit for the enclosure is configured and the features for each
circuit, see “Enclosed Power Circuits” in this chapter.
Identification System for Enclosed ALTIVAR Drives Excluding the ALTIVAR 56
An enclosed drive configuration number uses Class, Type and Modification Numbers to identify
the basic drive and optional devices. Fields 1 through 6 (see below) defines the basic type
number, and the options are defined by modification numbers. The 16 digit configuration number
that appears on all customer documents indicates the type and form number, and deletes the
field designation. This new 16 digit number will be compatible with future Square D product
selectors and Q2C systems.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
66U J G 4 V B A N C N A N N N N A, D
Field number:
Configuration number:
Type Number Modification Number

The configuration number for the enclosed drive breaks down into the following categories
Controller Style
Horsepower / 460 V
Enclosure Type
Voltage
Torque Applications
Power Circuit Type
Meter 1
Meter 2
General Purpose Devices
Special Purpose Pilot Devices
Option Board 1
(Future)
(Future)
(Future)
Dynamic Braking
Miscellaneous Options
1
66U
2
J
3
G
4
4
5
V
6
B
7
A
8
N
9
C
10
N
11
A
12
N
13
N
14
N
15
N
16
A, D
Field number:
Now, let’s suppose that a user calls in and requests an analog speed meter for their enclosure.
The following example demonstrates how a user’s modification is changed into a modification
letter and how that letter is displayed in the configuration number.
Example: A user has ordered an analog speed meter for their enclosed drive. If you look at the
chart below, you will see that the analog percent speed meter is A07 (from Table 4 of the Class
8839 ALTIVAR 66 Enclosed Adjustable Speed Drive Controllers Price Guide, Pub. No.
8839PL9601).
Meter 1 Mod Meter 2 Mod Meter Description Price
A07 A08 Analog Percent Speed $404.
B07 B08 Analog Percent Current 404.
C07 C08 Analog Percent Volts 404.
D07 D08 Analog Percent Power 404.
etc. etc. etc. etc.
Since the configuration number only uses a number or a letter in each field (except for field 1)
the A07 will then become an “A” for field 7 (see next page) when the full 16 digit configuration
number is displayed.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
66U J G 4 V B A N C N A N N N N A, D
Field number:
Class Number Type Number Modification
Number
Description
8829 66UJG4VB
A07
C09
A11
A16
D16
15hp @ 460 V, Type 1 enclosure,
variable torque, power circuit B
Analog speed meter
Start/stop push-button, speed pot
& Hand auto switch
(B1 Option) 24 V I/O extension
module
Red power on pilot light
Green run on pilot light
Remember: The drive controller nameplate and standard drawing documents will be identified
by the configuration number only.
Identification System for Enclosed ALTIVAR 56
An enclosed drive configuration number uses Class, Type and Modification Numbers to identify
the basic drive and optional devices. Fields 1 through 6 (see below) defines the basic type
number, and the options are defined by modification field, field 7. The 7 digit configuration
number that appears on all customer documents indicates the type and modification number,
and deletes the field designation. This new 7 digit number will be compatible with future Square
D product selectors and Q2C systems.
The configuration number for the enclosed drive breaks down into the following categories
Controller Style
Horsepower 1 - 100
Enclosure, G fixed
Voltage 2, 3 or 4
Torque Application V or L
Power Circuits W, Y, & Z
Modifications
1
56U
2 3
G
4 5 6Field number:
Type number:
7

MCC DRIVES
Definition of Motor Control Center (MCC) Type Drive
A MCC type drive is very similar to an enclosed type drive. Square D still does the pre-
engineering of the drive and enclosure. In the case of MCCs the Square D Seneca plant in
South Carolina integrates the drive into the MCC. The one difference between the enclosed type
and the MCC type is, that the drive is placed into a MCC bucket which is then integrated into the
MCC structure.
One of the considerations when installing a drive into a MCC is the temperature inside the
cabinet. To control the temperature, Square D uses a thermal management system. This system
circulates air across the heat sink of the drive itself. The advantage of this system is that the air
that is used for cooling the drive is never mixed with the internal air of the enclosure or the drive
structure. This system helps with keeping a constant temperature on the drive thus avoiding “hot
spot” problems. The thermal management system also assists in reducing environment
contaminants around the drive. Due to the thermal management system Square D does not have
any restriction on the drive placement in the MCC structure.
Identifying if a user has a MCC type drive will be covered in the section on “How To Identify The
Drive Type,” later in this chapter.
Which Square D AC Drives Can Be Used For MCC Type?
Of the drives covered in this course, the ALTIVAR 66 can be used for MCC type applications.

MCC Power Circuits
M
CB
AFC
DISC
MCC power circuits are almost like enclosed drive power circuits. The user still needs to choose
what power circuit configuration will be mounted into their enclosure. The user still has the same
factors to take into consideration when choosing a power circuit. The one difference when
working with MCC power circuits is that the MCC power circuits have different letter
designations. Letters, B, C, U, E, G, AND H are used to differentiate the power circuits in an
MCC. For a better understanding of how each power circuit is configured, see “MCC Power
Circuits” in this chapter.
Identification System
A MCC with an ALTIVAR drive catalog number uses MCC style, Disconnect Type, Unit Type,
Application code, Amperage rating, Power circuit, and Forms to identify the basic drive and
optional devices. Fields 1 through 6 (see below) defines the basic type number, and the options
are defined by forms numbers starting at field 7. The multi-digit catalog number that appears on
all customer documents indicates the type and form number for the MCC.
1 2 3 4 5 6 7 8 9
M6 B V C 7.6A B M09 P16 A16
10
AG16
11
PE35
etc.
etc.
Field number:
Type Number Forms Number(s)
Catalog number:

The catalog number for the MCC breaks down into the following categories
1 2 3 4 5 6 7 8 9
M6 B V C 7.6A B M09 P16 A16
10
AG16
11
PE35
etc.
etc.
Field number:
Type Number Forms Number(s)
Catalog number:
MCC Style
Disconnect Type
Unit Type
Application Code
Amp Rating
Power Circuit Type
Form(s)
When generating a MCC catalog number entry you enter the entire form code for each of the
form number fields. An example would be in the case of the form M09. Here you would enter in
both the letter and the number. For additional information on the different configurations and
options for MCCs with ALTIVAR drives reference the Model 6 Motor Control Center Price guide
(Order Number 8998PL9202R10/96), Electronic Equipment section.
MCC Drive Selection
The following information provides some general selection information on the ALTIVAR 66 MCC
drive packages from 1-200HP, 480V constant/variable torque or 1-75HP, 480V variable torque
low noise. Drives are available at this time in NEMA Type 1, Type 1 gasketed enclosures, &
Type 12 only. The drive units and options may be ordered as a “unit only device” and may be
retrofitted in Model 6 or Model 5 MCCs. Non-standard drives are not available without a
complete application, specification, and drawing review performed by your local Drives
Specialist.
Note: When retrofitting a drive to an existing MCC remember to compare the dimensions of the
new drive to the dimensions of the original drive. This is important because if the dimensions of
the new drive are larger that the original drive, the new drive may not fit in enclosure space
provided, and may require additional unit extender(s) for the additional space.
For Drive Selection:
1. Select all drives based on motor full load amperes. Horsepower is provided for convenience
only.
2. Select the drive catalog number based on application (torque) type i.e. variable torque,
constant torque or variable torque low noise. The drive will be factory programmed for the
selected catalog number. If you need assistance in selecting the drive catalog number or
reviewing the MCC specifications and drawings, or applications for the MCC, contact your
local Drives Specialist.

3. The drive catalog numbers include a basic power circuit with a disconnect, current limiting
fuses and drive controller. Select any optional contactors required for the application by
referring to Table A, “Power Contactor Options” (Model 6 Motor Control Center Price guide,
Order Number 8998PL9202R10/96, Electronic Equipment section) and changing the suffix
letter of the drive catalog number.
4. Select any control circuit devices by referring to Table B, “Pilot Devices” (Model 6 Motor
Control Center Price guide, Order Number 8998PL9202R10/96, Electronic Equipment
section) and adding the form numbers to the catalog number.
5. Select any miscellaneous features such as line reactors or extra control VA by referring to
Table C, “Miscellaneous Options” (Model 6 Motor Control Center Price guide, Order Number
8998PL9202R10/96, Electronic Equipment section) and adding the form numbers to the
catalog number.
Various drive options can be provided to meet the user’s specific requirements. Many of those
options or combinations of options may require additional mounting space or unit extender
modifications. When assisting a user with drive options and space requirements, contact the
Square D drives specialist, outside salesperson, or the MCC Technical Assistance Group (TAG)
for additional information or assistance.
IDENTIFYING THE DRIVE TYPE
Identify The Drive Type
Users will usually be calling to order a drive for one of the following reasons.
• new installation
• replacement drive for existing installation or
• duplicate drive for another application or for the same application.
For replacement or duplicate installations the following procedure to assist you in determining
whether the AC drive is mounted as an open type, enclosed type, or in a MCC.
1. Ask: Is the drive mounted in a Square D enclosure?
2. Use the following table to choose the procedure you want:
If the answer is . . . Then . . .
Yes
1. Get class and type number from the
enclosure data plate (usually, located
inside of the door or the exterior of the
enclosure). The number will start with the
8839 designator - that will help you
determine the type and style of drive in the
enclosure.
Note: If MCC have user look inside the drive’s
bucket for a data plate and locate the plant
code (Ex. 046 = Seneca) and Factory
Order number (F.O.). Then, cross
reference the F.O. number back to the
Square D drives specialist, outside
salesperson or the TAG group in Seneca
for complete drive specs.
2. Go to Step 3, below.

No
Note: Usually this will denote an open type
drive.
1. Get class or product number from the
name plate on the drive for the
identification.
Example: ATV66U41N4
I can’t find a name plate on the drive for
identification
1. Have the user power up the drive - press
the ESC key one time - this will give you
the drive identification screen which will
contain the product Identification number
Example: ATV66U41N4
Note: This technique will not give you the
option boards associated with the unit. You
have to physically look in the drive and see
if there is an option card installed.
3. Using your normal order entry methods, place the order for the drive.

ENCLOSED POWER CIRCUITS
The following pages show you the different power circuit configurations offered for the different
types of Class 8839 enclosures. These power circuits will become part of the part number when
ordering the enclosure.
8839 Power Circuit “A”
65kA
M
Fan
FFFC
AFC
FC = Fused Control
FF = Fused Fan
AFC = Adjustable Frequency Control Drive
• Lowest Economy-Optimized for NEMA 1 &
12 Enclosure
• No Disc Device or Bypass
• UL 508C listed for 65 kAIC
• Current limiting line fuses
•••• Control Transformer for Vent Fans
8839 Power Circuit “B”
65kA
M
Fan
FC FF
Disc.
AFC
Disc. = Disconnect
FC = Fused Control
FF = Fused Fan
• Moderate Economy-Optimized for NEMA 1
&12 Enclosure
• Includes Molded Case Disconnect Switch
• Control Transformer for Vent Fans

8839 Power Circuit “C”
22kA
M
Fan & Control
FC FO
MCP
OL
I B
AFC
MCP = Motor Circuit Protector
FC = Fused Control
FO = Fused Option
I = Isolation Contactor
B = Bypass Contactor
OL = Overload
• Lowest Economy-Integrated Iso & Bypass
Contactors for NEMA 1 & 12 Enclosure
• Includes MAG-GARD Breaker
8839 Power Circuit “D”
65kA
M
Fan & Control
FC FO
Disc.
OL
I B
FB
AFC
Disc. = Disconnect
FC = Fused Control
FB = Fused Bypass
FO = Fused Option
OL = Overload
• Moderate Economy-Integrated Iso/Bypass
Contactors for NEMA 1 & 12 Enclosure
• Includes Molded Case Switch

8839 Power Circuit “E”
22kA
M
Control
FC FO
XO
Disc.
OL
I B
MCP
Fan
FF
XF
AFC
Bypass Contactor
Compartment
Power Converter
Compartment
Disc. = Disconnect
FF = Fused Fan
FC = Fused Control
XF = Transformer Fan
XO = Transformer Option
FO = Fused Option
OL = Overload
• Lowest Economy-Barrier Iso/Bypass
Contactors NEMA 1 & 12 Enclosure
• Includes Molded Case switch &
MAG-GARD®
Breaker
•••• Includes 2-Control Transformers
8839 Power Circuit “F”
65kA
M
Control
FC FO
XO
Disc.
OL
I B
Disc.
Fan
FF
XF
FB
Bypass Contactor
Compartment
Power Converter
Compartment
AFC
Disc. = Disconnect
FF = Fused Fan
FC = Fused Control
FB = Fused Bypass
XF = Transformer Fan
FO = Fused Option
OL = Overload
• Moderate Economy-Barrier Iso/Bypass
Contactors NEMA 1 & 12 Enclosure
• Includes Two Molded Case Switches
•••• Includes 2-Control Transformers

8839 Power Circuit “G”
65kA
M
Fan
FC FO
Disc.
I
AFC
OL
Disc. = Disconnect
FC = Fused Control
FO = Fused Option
OL = Overload
• Moderate Economy-Integrated Output
Isolation Contactor for NEMA 1 & 12
Enclosure
8839 Power Circuit “H”
65kA max (Size 1-5)
M
Fan
Disc.
CL1
CL2
L
AFC
22kA max (Size 6-7)
or
Disc. = Disconnect
L = Line Contactor
CL1 = Control Line 1
• Moderate Economy-Integrated Input Line
Isolation Contactor NEMA 1 & 12
Enclosure

8839 Power Circuit “I”
65kA
M
FC
Disc.
OL
I B
Fan
FO
XO
AFC
User's
Starter
Disc. = Disconnect
FC = Fused Control
FO = Fused Option
OL = Overload
Isolation Contactor NEMA 1 & 12
Enclosure
8839 Power Circuit “J”
65kA
M
Fan
FC FO
Disc.
I
FA
CL1
CL2
L
FB
B
OL
AFC
Disc. = Disconnect
FC = Fused Control
FA = Fused
FB = Fused Bypass
FO = Fused Option
L = Line Contactor
OL = Overload
and Iso/Bypass Contactors for NEMA 1 &
12

8839 Power Circuit “K”
22kA max
M
Fan
MCP
I
CL1
CL2
L
B
OL
AFC
L = Line Contactor
OL = Overload
• Lowest Economy-Integrated Input Line and
Iso/Bypass Contactors for NEMA 1 & 12
• Includes MAG-GARD®
Breaker

ALTIVAR 56 Power Circuits
The following pages show you the different power circuit configurations offered for the different
types of Class 8839 ATV56 enclosures. These power circuits will become part of the part number
when ordering the enclosure.
Combination Package Power Circuit
22kA m ax
8.8kA m ax(208V)
FC
M CP
M
AFC
LC (ifused)
FC = Fused Control
LC = Line Contactor
Bypass Package Power Circuit
22kA m ax
8.8kA m ax(208V)
FC
M CP
M
AFC
LC (ifused)
Fan&
Control
Circuit
FF
IC BC
OL
FC = Fused Control
LC = Line Contactor
IC = Isolation Contactor
BC = Bypass Contactor
OL = Overload

Remote Starter Bypass Package Power Circuit
22kA m ax
8.8kA m ax(208V)
FC
M CP
M
AFC
LC (ifused)
Fan&
Control
Circuit
FF
IC BC
OL
User’s
Starter
FF = Fused Fan
FC = Fused Control
LC = Line Contactor
IC = Isolation Contactor
BC = Bypass Contactor
OL = Overload

MCC POWER CIRCUITS
Likewise, the following pages show you the different power circuit configurations offered for the
different types of MCC enclosures. These power circuits will become part of the part number
when ordering the MCC.
8998 Power Circuit “B”
M
CB
AFC
DISC
CB = Circuit Breaker
DISC = Disconnect
• Moderate Economy-Optimized for NEMA 1
&1A Enclosure
• Disconnect device - FS or CB
• UL 845 listed for 65 kAIC
8998 Power Circuit “C”
M
CB
AFC
I B
• Moderate Economy-Integrated Bypass for
NEMA 1 &1A Enclosure
• Disconnect device - CB only

8998 Power Circuit “U & E”
M
AFC
CB DISC DISC CB
DISC = Disconnect
• Moderate Economy-Barriered Bypass for
• “U” Barriered - NEMA cont.
• “E” Barriered Application Rated (Compac)
8998 Power Circuit “G”
M
AFC
CB DISC
DISC = Disconnect
• Moderate Economy-Output Contactor for
NEMA 1 & 1A Enclosure

8998 Power Circuit “H”
M
AFC
CB DISC
CL1
CL2
DISC = Disconnect
• Moderate Economy-Input Contactor for
• Auto Diagnostics

Use the information in this chapter to answer the following:
1. A user called and is looking for a replacement drive that they installed into their own cabinet,
what kind of drive type is the client looking for? ____________________________________
___________________________________________________________________________
2. When retrofitting a drive to an existing enclosure is it important to be concerned about the
physical dimensions of the drive?
___________________________________________________________________________
Why?
___________________________________________________________________________
3. What cooling system does Square D use when installing a drive into a Motor Control Center?
___________________________________________________________________________
4. The definition of an open drive type is?
___________________________________________________________________________
___________________________________________________________________________

SELF CHECK ANSWERS
Use the information in this chapter to answer the following:
1. A user called and is looking for a replacement drive that they have installed in their own
cabinet, what kind of drive type is the client looking for? The user has an open type drive
2. When retrofitting a drive to an existing enclosure is it important to be concerned about the
physical dimensions of the drive? Yes
Why?
This way you can verify that the drive will fit correctly into the user’s enclosure
3. What cooling system does Square D use when installing a drive into a Motor Control Center?
Thermal Management System
4. The definition of an open drive type is?
An open type drive is where the user buys the drive as a component piece, to use as is or
build into their own process or machine.

Introduction to AC Drives Chapter 5 - Helping Customers
Chapter 5 - Helping
Customers
LEARNING OBJECTIVES
• Be able to route a customer’s drive question to the appropriate person for assistance.
• Be able to gather basic customer drive application data for use by Square D personnel
in sizing a drive or selecting the appropriate drive product.

HELPING CUSTOMERS WITH AC DRIVE INQUIRIES
The preceding chapters have given you training in the fundamentals of AC motors, fundamentals
of AC drives, and introduced Square D AC drive products and AC drive types. The main
objective of this training has been to remove some of the mystery surrounding AC drives and
prepare you for further, more in depth training on AC drives if that is your desire. With the
knowledge you have now you can provide a service to your customers by answering as many
drive questions as you can, and by gathering vital application information from them to be
passed on to those more experienced in handling AC drive application and selection issues. A
glossary of terms is provided to assist you in quickly getting information about unfamiliar terms
or concepts.
The following job aids will help you to gather important customer drive application information
and to refer your customers to the proper persons to handle more technical drive issues.
Customer calls with an AC Drive inquiry:
Step 1 Use the following job aid to determine what service the customer requires:
Does Customer have
a Drive Order
Question?
Does Customer
Require Drive
Service?
Drive Specialist,
Outside Sales or
Raleigh Product
Support
Drive Specialist,
Outside Sales or
Raleigh Product
Support
Start up
Programming
Parts
On-Site
Return
Technical
If And Then Refer
YE
NO
Does Customer have
a Drive Application
Question?
Then
NO

Step 2 Complete the following AC Drive Application Worksheet
Sizing a drive or selecting the correct drive for an application starts with gathering information
about the customer’s application. Gather as much information as you can from the customer
using this worksheet. After completing the worksheet provide a copy of it to the person who will
be sizing and selecting the appropriate drive for the customer’s application. You may want to
make additional copies of this worksheet.
AC Drive Application Worksheet
CUSTOMER DATA:
Company Name: ________________________________________ Date: ________________
Address: ____________________________________________________________________
____________________________________________________________________
Contact: _____________________________________ Phone: (______)__________________
Fax: (______) _________________________________
MOTOR DATA:
NEMA Motor Type:
NEMA A NEMA B NEMA C NEMA D
Synchronous Reluctance Other
If “Other”, describe: __________________________________________________________
Motor Nameplate Data:
HP ________ Voltage 3PH ______ Hz ______ Poles _____ FLA ______ LRA _____
RPM ______ Enclosure Type _____________ Frame ___________ Mounting _________
Insulation Class _____________________________ Service Factor ___________________
Gear Box Type ____________________ Ratio __________________
APPLICATION DATA:
Application (Type of machinery or equipment) ________________________________________
_____________________________________________________________________________
Type of Load (if unsure, see - Table 1: Application Characteristics of Typical Loads):
Constant Torque ______ Constant HP _______ Variable Torque ______ Impact ______
Other _________________________________________________________________
Measured Load Running __________ Amps Peak Load _____________ Amps
APPLICATION DATA (CONT)

Duty Cycle Per Hour _________________________________________________________
If Applicable, Create Time Vs Load Graph _________________________________________
Speed Range Required ____________ Minimum Speed to _____________ Maximum Speed
Is High Breakaway Torque Required? YES NO
Speed Regulation Required? YES NO If Yes, Specify ________ % of Base Speed
Is Acceleration or Deceleration Time Critical? YES NO
If Yes, Answer Questions Below:
Load Inertia: _________________ Lb. Ft.
2
Acceleration Requirement: Minimum _______ seconds Maximum _______ seconds
Deceleration Requirement: Minimum _______ seconds Maximum _______ seconds
ENVIRONMENT:
Input Line _________ Volts ± __________ % ___________ Phase __________ Hertz
Drive Controller Enclosure Type: Open Type NEMA 1 NEMA 12
Other (Specify): _____________________________________________________________
Temperature (Ambient) ____________ °C (°F) to _______________ °C (°F)
Altitude - If Drive Controller Is Greater Than 3300 Ft. Above Sea Level, Specify: __________
Are There Any Other Conditions Or Data Which May Effect Drive Sizing? If Yes, Please Specify:
_____________________________________________________________________________
CONTROL:
Indicate Type of Control Scheme Required:
Start _______ Hand-Auto _______
Stop _______ Run-Jog _______
Start/Stop Push-button _______ Hand-OFF-Auto _______
Forward-Reverse _______ Power ON Pilot Light _______
Other types of control not listed above
_______________________________________________
Speed Reference by Manual Speed Potentiometer _______
Fail Pilot Light _______

APPLICATION CHARACTERISTICS OF TYPICAL LOADS
This table lists the typical load characteristics - use it as a guideline only. If you have a question
about the type of load for an application, confirm this information with the machinery
manufacturer.
Table 1: Application Characteristics of Typical Loads
Application Load Breakaway
Torque
Application Load Breakaway
Torque
Agitators Machines
Liquid *VT Moderate Boring CT Moderate
Slurry *VT Moderate Bottling CT Moderate
Blowers Milling *CHP Moderate
Centrifugal VT Low Mills
Positive Displacement CT Low (Unloaded) Rolling *CT Moderate
Calenders CT Low Rubber *CT Moderate
Card Machines CT Moderate Mixers
Centrifuges CT Moderate Chemical CT High
Chippers *CT High Dough CT High
Compressors Slurry CT High
Axial - Centrifugal VT Low Planers CT Moderate
Reciprocating *CT Moderate Plows - Conveyor CT Moderate
Rotary CT Moderate Presses
Conveyors Printing CT Moderate
Belt CT Moderate Punch *CT Moderate
Screw *CT High Pullers - Car CT Moderate
Shaker *CT Moderate Pumps
Cranes Centrifugal VT Low
Bridge CT Moderate Positive Displacement CT Moderate
Trolley CT Moderate Slurry CT High
Hoist CT Moderate Roll Benders CT Moderate
Crushers *CT High Sanders CT Low
Drill Presses CHP Moderate Saws *CT Moderate
Elevators CT Moderate Shakers *CT High
Extruders CT Moderate Shears *CT Low
Fans - Centrifugal VT Low Tension Drives CHP Moderate
Frames - Spinning CHP Low Tool Machines CHP Moderate
Grinders CHP Moderate Walkways CT Low
Kilns CT High Winches CT Moderate
Looms CT Moderate Winders CHP Moderate
Lathes *CHP Moderate Washers CT Moderate
VT = Variable Torque High = Greater than 150% Torque
CT = Constant Torque Moderate = Between and Including 100% to 150% Torque
CHP = Constant Horsepower Low = Less than 100% Torque
* = Potential Impact Load
Step 3 - After completing the Application Data Worksheet, refer the customers’ question along
with the application information you have gathered, to the appropriate technical person (drives
specialist, outside salesperson or product support group) to assist the customer in sizing a drive
or selecting the appropriate product.

Introduction to AC Drives Appendix A
APPENDIX A
SELF ASSESSMENT STUDY
GUIDE ANSWERS

SELF ASSESSMENT STUDY GUIDE ANSWERS
1. The armature of a motor consists of D .
A. the housing and rotor
B. the shaft and stator
C. the stator and housing
D. the shaft and rotor
2. The magnetic fields of the stator and rotor are changed according to the B .
3. The speed of the rotor is determined by the B .
4. The difference between a motor’s synchronous and actual rotor speed is called the C .
A. Variable torque
B. Dynamic speed
C. Slip
D. Magnetic flux
5. The torque a motor produces is directly related to A .
6. The maximum torque that a motor can produce is called: C .
A. Full load torque
B. Constant torque
C. Breakdown torque
D. Overload toque
7. A motor’s service factor indicates the: D .
A. Approximate life expectancy of the motor if applied within the rated nameplate
parameters
B. The NEMA rating of the motor which is comparable to the torque performance of the
motor.
C. Electrical power supplied to the motor.
D. Overloads which may be carried by the motor without exceeding the maximum
temperature recommended for the insulation
If you answered questions 1 - 7 correctly you may skip the
training presented in Chapter 1 - AC Motor Fundamentals

8. Match the components of an AC drive with their function:
B Inverter A. This section smoothes rectified DC before it goes
A DC bus filtering B. This section changes DC into an adjustable frequency
synthetic AC
C Converter C. This section changes 60 Hz AC power into DC
9. The difference between a soft start and an AC drive is: A .
A. That the soft start reduces voltage and current at startup
B. That an AC drive controls motor startup by reducing startup torque.
C. That a soft start can be used in place of an AC drive
D. All of the above
E. None of the above
10. Maintaining the volts per Hertz ratio is necessary because: B .
A. In order to accurately measure a given motor’s speed then the ratio of both the voltage
and frequency must be maintained.
B. When a motor is running at less than full speed maintaining this ratio provides a method
of keeping the magnetic flux constant, thus producing full load-torque.
C. The voltage and frequency coming from the power generating station may varies in both
voltage and frequency.
D. The horsepower of the motor is dependent upon this ratio.
11. With a constant torque load: A .
A. Torque remains the same as the speed changes.
B. Horsepower varies inversely with the speed.
C. Torque remains the same as the current changes.
D. All of the above.
training presented in Chapter 2 - AC Drive Fundamentals
12. B AC drives can only be ordered as replacements to existing equipment.
A. ALTIVAR
B. OMEGAPAK
C. ALTIVAR and OMEGAPAK
D. There are no limited offerings with AC drives

13. The complete ALTIVAR family consists of D .
A. ALTIVAR 16, 26, 55, and 67
B. ALTIVAR 8803, 8804, 16, and 18
C. ALTIVAR 8803 and 8804
D. ALTIVAR 16, 18, 56, and 66
14. The ALTIVAR drives meet A standards.
A. ISO 9000 series, and UL, CSA, IEC, VDE
B. UL, CSA, IEC, VDE
C. ISO 9000, ISO 3000 series, and UL, VDE
D. ISO 9007 series, and UL, CSS, ICC, VDE
15. C are the major components for Dynamic Braking.
A. Jumper J-12 to switch a resistor circuit in and out, and a separately mounted brake
B. A separately mounted semi-conductor circuit and resistor R-7
C. A power semi-conductor to switch resistor circuit in and out, and a separately mounted
braking resistor
D. A power semi-conductor to switch resistor circuit in and out, and three separately
mounted braking resistors
training presented in Chapter 3 - Square D AC Drive Products
16. An open type drive is bought as A .
A. As a component piece
B. As a total Square D enclosure
C. As a total Square D MCC
D. All of the above
17. C drive(s) can be used for open type applications.
A. OMEGAPAK 8803 and 8804
B. ALTIVAR 16, 18
C. ALTIVAR 16, 18, 56, and 66
D. ALTIVAR 16, 18, 56, 66, and OMEGAPAK 8803 and 8804
18. Enclosed type drives are manufactured at the B .

19. B drive(s) can be used for MCC applications.
A. OMEGAPAK 8803
B. ALTIVAR 66
C. ALTIVAR 16
D. ALTIVAR 56
20. The MCC drive packages can be from D .
A. 1-50HP, 220V constant/variable torque or 1-25HP, 480V variable torque low noise
B. 1-800HP, 240V constant/variable torque or 1-75HP, 400V variable torque high noise
C. 1-50HP, 480V constant/variable torque or 1-250HP, 480V variable torque no noise
D. 1-200HP, 480V constant/variable torque or 1-75HP, 480V variable torque low noise
21. Enclosed Type drives are offered in A .
A. NEMA Type 1 and Type 12 enclosures
B. NEMA Type 1, Type 3, and Type 12 enclosures
C. NEMA Type 12 enclosures
D. NEMA Type 4 and Type 12 enclosures
training presented in Chapter 4 - AC Drive Characteristics & Types

Introduction to AC Drives Glossary of Terms
GLOSSARY
OF
TERMS

GLOSSARY OF TERMS
120/240 Voltage System Most commonly used in residential applications,
by using this (single phase 3 wire) system 120
volts is available between phase and neutral
and 240 volts is available phase-to-phase.
240 Volt Delta system: This is an uncommon (regional) system used in
light industrial applications. This (3 phase 3
wire) system provides 240 volts phase to phase.
The NEC requires most of these systems to be
grounded hence the name “Grounded B phase”.
This system requires careful selection and
installation of electrical equipment, particularly
circuit breakers and motor controllers.
240/120 Delta System Most commonly referred to as a “Wild Leg”
system. (3 phase 4 wire) 240 volts is available
between phases and 120 volts is available
between two of the phases and the neutral
which is grounded (usually the A and C phases).
It should be noted that between the B phase and
ground 208 volts is available.
208Y/120 Volt Wye System Common system for commercial applications.
By using this (3 phase 4 wire) system: 120 volts,
for lighting and receptacle loads, is available
between any phase and neutral; and 208 volts,
for motors and heating loads, is available phase
to phase.
480 Volt Delta system: Very common system in large industrial
applications. This (3 phase 3 wire) system is
usually installed ungrounded and requires
maintenance by “qualified persons”. Electrical
equipment installed on this system must be
rated 480V phase to ground as well as phase to
phase.
480Y/277 Volt Wye System: The most common system in large commercial
and industrial applications. By using this (3
phase 4 wire) system: 277 volts, for lighting
loads, is available between any phase and
neutral; and 480 volts, for motors and heating
loads, is available phase to phase.
AA (med. voltage transformers) Abbreviation for Air-To-Air. Self-cooled by
convection and conduction as it applies to a dry-
type transformer, i.e. the heat transfer path.

Adjustable Speed The concept of varying the speed of a motor,
either manually or automatically. The desired
operating speed (set speed) is relatively
constant regardless of load.
Adjustable Speed Drive (Electrical) The adjustable speed drive is comprised of the
motor, drive controller and operator’s controls
(either manual or automatic).
AIC Ampere interrupting capacity. See AIR or
ampere interrupting rating.
AIR Ampere Interrupting rating. The highest current
at rated voltage that a circuit breaker is intended
to interrupt under standard test conditions.
Alternating current This is the most common type of current used
today. In the United States, all electricity is
generated as alternating current. It is called
alternating current because first the current
flows in one direction then it will flow in the
opposite direction and so on. The current
alternates between two opposite directions. (It is
often represented by a side-ways “s”) Alternating
current is used in homes for lighting, heating,
cooking, and operating appliances. Industry
uses it primarily to operate motors but also for
lighting and equipment operation. The
abbreviation for alternating current is “AC”.
Ambient Noise Level The noise level of the surrounding area
measured in decibels.
Ambient Temperature Temperature of the surrounding atmosphere
into which the heat of any electrical product is
dissipated.
Ambient Temperature Rating Temperature at which the continuous current
rating (handle rating) of a circuit is based; the
temperature of the air immediately surrounding
the circuit breaker that can affect the thermal
(overload) tripping characteristics of a thermal-
magnetic circuit breaker. Electronic trip circuit
breakers, however, are insensitive to normal (-
5
o
to 50
o
C) ambient conditions. UL standard
489 listed circuit breakers have an ambient
temperature rating of 40
o
C.
ANSI American National Standards Institute
ANSI 49 Shade of gray paint color. Standard means of
describing paint color with the number indicating
the percentage of reflected light. (ANSI 0 would
be black, ANSI 100, totally reflective).

Armature (motor) An assembly composed of the rotor and the shaft.
ASTM American Society for Testing Materials
ATC (m.v. transformers) Air terminal compartment (i.e., air-filled as
opposed to oil-filled). Space in which to
terminate cable connections to a transformer.
Automatic Protection Circuit A device which automatically (no human action
needed) disconnects power. For an example, a
circuit breaker is both a manual and automatic
device. A person can manually open a circuit
breaker or it can automatically open if it senses
an overcurrent condition.
Axis A principle direction along which movement of
the tool or workpiece occurs. The term axis also
refers to one of the reference lines of a
coordinate system.
Back of a Motor The back of a motor is the end which carries the
coupling or driving pulley (NEMA). This is
sometimes called the drive end (D.E.) or pulley
end (P.E.).
Bandwidth Generally, frequency range of system input over
which the system will respond satisfactorily to a
command.
Base Speed Base speed is the manufacturer’s nameplate
rating where the motor will develop rated HP at
rated load and voltage. With DC drives, it is
commonly the point where full armature voltage
is applied with full rated field excitation. With
AC systems, it is commonly the point where 60
Hz is applied to the induction motor.
Bearing (Ball) A “ball” shaped component that is used to
reduce friction and wear while supporting
rotating elements. For a motor, this type of
bearing provides a relatively rigid support for the
output shaft.
Bearing (Roller) A special bearing system with cylindrical rollers
capable of handling belted load applications, too
large for the output shaft.
BIL Basic Insulation Level. A specific insulation
level expressed in kilovolts of the crest value of
a standard lightning impulse.
Bolt-on Connection (motor control centers) Interior device is cable-connected directly to the
horizontal bus by means of bolted connection.

Branch Circuit An electrical path which connects to the main
electrical path. If a branch is disconnected from
the main branch only the load connected to that
branch looses power. All other branches are not
affected by the disconnection.
Branch Circuit Breaker Switch which is connected to the main circuit
path and the first load in the branch. It is used to
turn off power to that branch circuit.
Breaking Breaking provides a means of stopping an AC
or DC motor and can be accomplished in
several ways:
A. Dynamic Braking (DC Drives) --- slows the
motor by applying a resistive load across the
armature leads after disconnection from the
DC supply. This must be done while the
motor field is energized. The motor then acts
as a generator until the energy of the rotating
armature is dissipated. This is not a holding
brake.
Dynamic Braking (AC Drives) --- Since AC
motors do not have separate field excitation,
dynamic braking is accomplished by
continuing to excite the motor from the drive.
This causes a regenerative current to the
drive’s DC Intermediate Bus Circuit. The
Dynamic Brake resistors are then placed
across the DC bus to dissipate the power
returned. The brake resistor is usually
switched by a transistor or other power switch
controlled by the drive.
B. Regenerative Braking --- is similar to
Dynamic Braking, but is accomplished
electronically. The generated power is
returned to the line through the power
converter. It may also be dissipated as losses
in the converter (within its limitations).
C. Motor Mounted or Separately Mounted Brake
--- is a positive action, mechanical, friction
device. Normal configuration is such that
when the power is removed, the brake is set.
This can be used as a holding brake. (Note:
A Separately Mounted Brake is one which is
located on some part of the mechanical drive
train other than the motor.)

Breakaway Torque The torque required to start a machine from
standstill. It is always greater than the torque
needed to maintain motion.
Breakdown Torque The breakdown torque of an AC motor is the
maximum torque which it will develop with rated
voltage applied at the rated frequency.
Bridge Rectifier A full wave rectifier that conducts current in only
one direction of the input current. AC applied to
the input results in approximate DC at the
output.
Bridge Rectifier (Diode, SCR) A diode bridge rectifier is a non-controlled full
wave rectifier that produced a constant rectified
DC voltage. An SCR bridge rectifier is a full
wave rectifier with an output that can be
controlled by switching on the gate control
element.
Bushing (m.v. transformers) Conductor extending through the tank wall with
liquid-tight fittings for connecting electrical
internal parts to exterior cables.
“C” Face (Motor Mounting) This type of motor mounting is used to close
couple pumps and similar applications where
the mounting holes in the face are threaded to
receive bolts from the pump. Normally, the “C”
face is used where a pump or similar item is to
be overhung on the motor. This type of
mounting is a NEMA standard design and
available with or without feet.
Cable Tray (wire mgmt.) An economical system for supporting cables
and wires.
Case (motor) The external housing of the motor
Cellular Steel Floor System (wire mgmt.) Corrugated sheet metal floor decking which can
be used as electrical raceway.
Circuit Breaker A device designed to open and close a circuit by
non-automatic means and to open the circuit
automatically on a predetermined overcurrent
without damage to itself when properly applied
within its rating.
Circuit Breaker Frame 1. The circuit breaker housing that contains the
current carrying components, the current
sensing components and the tripping and
operating mechanism. 2. That portion of an
interchangeable trip circuit breaker remaining
when the interchangeable trip unit is removed.

Closed Loop Closed loop refers to a regulator circuit in which
the actual value of the controlled variable (e.g.
speed) is sensed and a signal proportional to
this value (feedback signal) is compared with a
signal proportional to the desired value
(reference signal). The difference between
these signals (error signal) causes the actual
value to change in the direction that will reduce
the difference in signals to zero.
Cogging A condition in which a motor does not rotate
smoothly but “steps” or “jerks” from one position
to another during shaft revolution. Cogging is
most pronounced at low motor speeds and can
cause objectionable vibrations in the driven
machine.
Common Mode Noise (power conditioning) This is electrical interference that occurs
between the hot wire and ground, or the neutral
wire and ground.
Common Trim (lighting panels) One piece of sheet metal which covers two
panelboards mounted side by side.
Commutation (Inverter) The process by which forward current is
interrupted or transferred from one switching
device to the other. In most circuits where power
is supplied from an AC source, turn-on control is
adequate and turn-off occurs naturally when the
AC cycle causes the polarity across a given
device to reverse.
Comparator A device that compares one signal to another.
This is usually the process signal which is
compared to the set point or command signal.
Compartment Space (air-filled) in which to terminate cable.
Conductor Materials that allow current to flow easily. The
“pipe” for electrons.
Constant Horsepower Range A range of motor operation where motor speed
is controlled by field weakening. In this range,
motor torque decreases as speed increases.
Since horsepower is speed times torque
(divided by a constant), the value of horsepower
developed by the motor is this range is constant.
Constant Torque Range A speed range in which the motor is capable of
delivering a constant torque, subject to the
cooling limitations of the motor.

Constant Voltage Range (AC Drives) The range of motor operation where
the drive’s output voltage is held constant as the
output frequency is varied. This speed range
produces motor performance similar to a DC
drive’s constant horsepower range.
Constant Volts per Hertz (V/Hz) This relationship exists in AC drives where the
output voltage is varied directly proportional to
frequency. This type of operation is required to
allow the motor to produce constant rated torque
as speed is varied.
Contactor Reversing A method of reversing motor rotation by the use
of two separate contactors, one of which
produces rotation in one direction and the other
produces rotation in the opposite direction. The
contactors are electrically (and mechanically)
interlocked so that both cannot be energized at
the same time.
Continuous current rating (handle rating) The maximum direct current or rms current in
[circuit breakers] amperes, at a rated frequency
which a device or an assembly will carry
continuously without exceeding the specified
limits of observable temperature rise.
Continuous Duty (CONT) A motor that can continue to operate
within the insulation temperature limits after it
has reached normal operating (equilibrium)
temperature.
Continuous Load A load where the maximum current is expected
to continue for three hours or more.
Continuous Rating Defines the constant load which a transformer
can carry at rated primary voltage and
frequency without exceeding the specified
temperature rise.
Converter The process of changing AC to DC. This is
accomplished through the use of a diode
rectifier or thyristor rectifier circuit. The term
“converter” may also refer to the process of
changing AC to DC to AC (e.g. adjustable
frequency drive). A “frequency converter”, such
as that found in an adjustable frequency drive,
consists of a Rectifier, a DC Intermediate
Circuit, an Inverter and a Control Unit
Core Loss (transformers) The energy lost in the transformer needed to
magnetize the core. Expressed in watts of KW
(1000 watts). Core loss is constant and
independent of transformer load. It is present all
the time a transformer is energized. (See also
Iron Loss, No-Load Loss.)

Corrosion Resistant "Corrosion Resistant" means that a device is so
constructed, protected, or treated that corrosion
will not exceed specified limits under specific
test conditions.
CSA Canadian Standards Association.
Current (electrical service) Alternating current (AC) or direct current (DC)
Current (represented as an “I”) The flow of electrons. Current is measured in
amperes, (commonly abbreviated as “amps”).
Current Limiting An electronic method of limiting the maximum
current available to the motor. This is adjustable
so that the motor’s maximum current can be
controlled. It can also be preset as a protective
device to protect both the motor and control
from extended overloads.
Current-Limiting Circuit Breaker A circuit breaker that does not use a fusible
element and when operating within its current
limiting range, limits the let through current
within predetermined acceptable values.
Damping Damping is the reduction in amplitude of an
oscillation in the system.
Dead Band The range of values through which a system
input can be changed without causing a
corresponding change in system output.
Decibel (dB) A term used in sound measurement. A change
of one dB in sound level is the smallest change
the human ear can detect. A busy office might
measure from 65-70 dB. dB is a measure of
sound intensity.
Delta (∆) A standard three-phase connection with the
ends of each phase winding connected in series
to form a closed loop with each phase 120
degrees from the other. Sometimes referred to
as 3-wire.
Delta Voltage System This system provides three phases and three
wires, three “hot” wires. 240 volt and 480 volt
are the most commonly used delta systems.
Delta-Wye A term or symbol indicating the primary
connected in delta and the secondary in Wye
when pertaining to a three-phase transformer or
transformer bank.
Deviation Difference between an instantaneous value of a
controlled variable and the desired value of the
controlled variable corresponding to the set
point. Also called error.

“D” Flange (Motor Mounting) This type of motor mounting is used when the
motor is to be built as part of the machine. The
mounting holes of the flange are not threaded.
The bolts protrude through the flange from the
motor side. Normally “D” flange motors are
supplied without feet since the motor is mounted
directly to the driven machine.
di/dt The rate of change in current versus a rate of
change in time. Line reactors and isolation
transformers can be used to provide the
impedance necessary to reduce the harmful
effects that unlimited current sources can have
on phase controlled rectifiers (SCRs).
Dielectric Insulator such as glass, rubber, plastic, etc. that
separates two electrical conductors in a
transformer or capacitor, for example.
Diode A device that passes current in one direction,
but blocks current in the reversed direction.
Distribution Transformers Transformers rated 500KVA and below are
usually referred to as distribution type.
Exceptions include current and potential and
other specialty transformers.
Direct current This can be produced from alternating current or
supplied as a direct output from a battery. Direct
current always flows in the same direction. In
the United States, direct current powers cranes
and other industrial equipment. The
abbreviation for direct current is “DC”.
Door-In-Door (lighting panels) Trim has an inner door over the branch
disconnect area secured with one latch. An
outer door covers the gutter area also secured
by a single latch. There is another flange around
the entire box.
Double or Split Door (lighting panels) In a lighting contactor panel, one door is used to
cover the contactor and the other is used to
cove the branch breakers.
Drift Drift is the deviation from the initial set speed
with no load change over a specific time period.
Normally the drive must be operated for a
specified warm-up time at a specified ambient
temperature before drift specifications apply.
Drift is normally caused by random changes in
operating characteristics of various control
components
Driptight "Driptight" means that a device is so constructed
or protected as to excluded falling dirt or drops
of liquid under specified test conditions.

Drive Controller (Also called Variable Speed Drive) An electronic
device that can control the speed, torque,
horsepower and direction of an AC or DC motor.
Dry Type (transformers) A dry type transformer is one in which the
transformer core and coils are immersed in air
or other dry gas.
Dusttight "Dusttight" means that a device is so
constructed so that dust will not enter the
enclosure case under specified test conditions.
DutyCycle The relationship between the operating and rest
times or repeatable operation at different loads.
dv/dt The rate of change in voltage versus a rate of
change in time. Specially designed Resistor-
Capacitor networks can help protect the SCRs
from excessive dv/dt which can result from line
voltage spikes, line disturbances and circuit
configurations with extreme forward conducting
or reverse blocking requirements.
Dwell The time spent in one state before moving to
the next. In motion control applications for
example, a dwell time may be programmed to
allow time for a tool change or part clamping
operation.
Dynamic Braking See Braking
Eddy Current Currents induced in motor components from the
movement of magnetic fields. Eddy currents
produce waste heat and are minimized by
lamination of the motor poles and armature.
EEMAC Acronym for Electrical and Electronic
Manufacturer's Association of Canada. Similar
to NEMA in the U.S.
Efficiency Ratio of mechanical output to electrical input
indicated by a percent. In motors, it is the
effectiveness with which a motor converts
electrical energy into mechanical energy.
Efficiency (transformers) The efficiency of a transformer is the energy
output expressed as a percentage of the energy
input and reflects the losses within the
transformer. For loads between 25% and 150%
of rating efficiencies between 98% and 99.5%
would not be untypical.
Electrical Service Supply power from the utility.

Electrostatic Shield (transformers) Copper or other conducting sheet placed
between primary and secondary and grounded
to provide additional protection against electrical
interference.
Empty Mounting Units (motor control centers) Includes a removable undrilled panel with a
hinged door to provide space for customer-
installed devices in a Motor Control Center.
Enable To allow an action or acceptance of data by
applying an appropriate signal to the appropriate
input.
Encapsulated Winding (transformers) Transformer having coils either dipped or cast in
an epoxy resin.
Enclosure Enclosure refers to the housing in which the
control is mounted. Enclosures are available in
designs for various environmental conditions.
Enclosure Temperature (transformers) Sum of the ambient temperature and the
temperature rise of the enclosure allowed by
standards.
Encoder An electromechanical transducer that produces
a serial or parallel digital indication of
mechanical angle or displacement. Essentially,
an encoder provides high resolution feedback
data related to shaft position and is used with
other circuitry to indicate velocity and direction.
The encoder produces discrete electrical pulses
during each increment of shaft rotation.
Equipped Space (motor control centers) This is sometimes requested as space for future
units in a Motor Control Center. Fully bussed
space is available for future starter units.
Error Difference between the set point signal and the
feedback signal. An error is necessary before a
correction can be made in a controlled system.
Excitation Current The steady state current that keeps the
transformer energized after the inrush has
dissipated.
Exciting Current Current which flows in any winding used to
excite the transformer when all other windings
are open-circuited and is usually expressed in
percent of the rated current of a winding in
which it is measured.
Eye-Bolt Bushing (m.v. transformers) Bushing with integral screw clamp for one cable
only.

FA (m.v. transformers) Forced Air. Indicated cooling by virtue of fans to
provided forced air-flow. Always used in
conjunction with the self-cooled designation as
in OA/FA or AA/FA.
FCAN (transformers) Full capacity above normal nameplate voltage.
FCBN (transformers) Full capacity below nominal. Abbreviation
which, when pertaining to transformers,
designated that they are suitable for full-rated
KVA at voltages below rated level.
FFA (m.v. transformers) Future forced air. Indicated provisions have
been made for field installation of forced-air
cooling. (See also FA.)
Feedback The element of a control system that provides
an actual operation signal for comparison with
the set point to establish an error signal used by
the regulator circuit.
Filter A device that passes a signal or a range of
signals and eliminates all others.
Floating Ground A circuit whose electrical common point is not at
earth potential or the same ground potential as
circuitry it is associated with. A voltage
difference can exist between the floating ground
and earth ground.
Force The tendency to change the motion or position
of an object with a push or pull. Force is
measured in ounces or pounds.
Four-Quadrant Operation The four combinations of forward and reverse
rotation and forward and reverse torque of
which a regenerative drive is capable. The four
combinations are:
1. Forward rotation/forward torque (motoring)
2. Forward rotation/reverse torque regeneration)
3. Reverse rotation/reverse torque (motoring)
4. Reverse rotation/forward torque regeneration)
Frame Size (Motors) The physical size of a motor, usually consisting
of NEMA defined “D” and “F” dimensions at a
minimum. The “D” dimension is the distance in
quarter inches from the center of the motor
shaft to the bottom of the mounting feet. The “F”
dimensions relates to the distance between the
centers of the mounting feet holes.
Frame Size (circuit breakers) A term applied to a group of molded case circuit
breakers which are physically interchangeable
with each other. Frame size is expressed in
amperes and corresponds to the largest ampere
rating available in the group.

Frequency The number of cycles per second for an AC
electric system; the number of times per second
that the current flow changes direction.
Frequency of Current (electrical service) This applies only to alternating current (AC). In
the United States it is usually 60 hertz. Outside
the United States 50 hertz is common.
Front of a Motor The end opposite the coupling or driving pulley
(NEMA). This is sometimes called the opposite
pulley end (O.P.E.) or commutator end (C.E.).
Full-Capacity Tap (transformers) Tap through which the transformer can deliver
its rated KVA output without exceeding the
specified temperature rise.
FLC (motor control) This is the electrical current required during
normal motor operation to generate its designed
horsepower. Full load current is also known as
full load amps (FLA). A motor’s full load current
is used when selecting motor overload
protection devices.
Full-Load Torque The full-load torque of a motor is the torque
necessary to produce rated horsepower at full-
load speed.
Fully Rated Selectively Coordinated This is a fully rated system with an additional
system (circuit breakers) design characteristic:
within the range of selectivity, overcurrent
protective device closest to the fault, opens the
circuit, while the upstream overcurrent
protective device remains closed. This limits
unnecessary interruption of service to
unaffected portions of the system. A system
coordination study may be advisable to assure
optimum selectivity.
Fully Rated System (circuit breakers) In this system, the interrupting rating of all
overcurrent protective devices must be greater
than or equal to the available fault current at the
lineside terminals of each device.
Gate The control element of an SCR (silicon
controlled rectifier) commonly referred to as a
thyristor. When a small positive voltage is
applied to the gate momentarily, the SCR will
conduct current (when the anode is positive with
respect to the cathode of the SCR). Current
conduction will continue even after the gate
signal is removed.
Generators Large machines which produce electricity.
Generators are found in electrical power plants.

GTO Gate turn-off or gate turn-on power
semiconductor device.
General-Purpose Motor This motor has a continuous Class “B” rating
and design, listed and offered in standard
ratings with standard operating characteristics
and mechanical construction for use under usual
service conditions without restriction to a
particular application or type of application
(NEMA).
Handle Rating (circuit breakers) See continuous current rating.
Harmonic A component frequency of a current or voltage
that is an integral multiple of the fundamental
frequency.
Hertz A unit of frequency equal to one cycle per
second. Abbreviated Hz.
High Power Factor When the active power component equals or is
very near to the total power such as for a purely
resistive load, the highest power factor possible
would be 1.0, or 100% unity.
Hinged Trim (lighting panels) Alternative to door-in-door construction. Has
piano hinge on one side, door opens by a single
latch.
Horsepower The amount of work done by a machine.
Relative to motors, horsepower Indicates the
power of the motor. Motor horsepower is a
selection criterion for motor control products
such as manual and magnetic motor starters.
Hunting Undesirable fluctuations in motor speed that can
occur after a step change in speed reference
(either acceleration or deceleration) or load.
Hysteresis Loss The resistance offered by materials to becoming
magnetized results in energy being expended
and corresponding loss. Hysteresis loss in a
magnetic circuit is the energy expended to
magnetize and demagnetize the core.
IEEE Institute of Electrical and Electronic Engineers.
IGBT (Insulated Gate Bipolar Transistor) - Type of
power device frequently used in inverter
sections of drives. The IGBT is noted for its
ease in switching on and off and high switching
frequencies.

Impedance (%IZ) Retarding forces of current flow in ac circuits.
With respect to transformers, it is the measure
of the transformer’s resistance and reactance to
current flow.
Induction Motor An alternating current motor in which the
primary winding on one member (usually the
stator) is connected to the power source. A
secondary winding on the other member
(usually the rotor) carries the induced current.
There is no physical electrical connection to the
secondary winding, its current is induced.
Inductive Loads Any type of load that has a coil of wire as the
current-drawing element (i.e. motor winding,
ballast, transformer).
Inertia A measure of a body’s resistance to changes in
velocity, whether the body is at rest or moving
at a constant velocity. The velocity can be either
linear or rotational. The movement of Inertia
(WK
2
) is the product of the weight (W) of an
object and the square of the radius of gyration
(K
2
). The radius of gyration is a measure of how
the mass of the object is distributed about the
axis of rotation. WK
2
is usually expressed in
units of lb-ft
2
.
Input devices (motor control) Control products that start the initial action of a
control system. These devices send electrical
signals to a second type of product called logic
devices.
Inrush (motor) High initial peak of current occurring during the
first few cycles of motor energization.
Instability The state or property of a system where there is
an output but no corresponding input.
Insulator Materials that do not allow current to flow easily.
It is wrapped around individual wires to prevent
the current flow to undesirable places.
Isolation (power conditioning) The magnetic separation of the input and output
of a transformer device with a grounded shield
in between them.
Insulation System Balancing of insulation materials to properly
insulate a given product.
Integral Horsepower Motor A motor built in a frame having a continuous
rating of 1 HP or more.
Integral Main (lighting panels) The main disconnect device is inside the
panelboard.

Intermittent Duty (INT) A motor that never reached equilibrium
temperature (equilibrium), but is permitted to
cool down between operations. For example, a
crane, hoist, or machine tool motor is often
rated for 15 or 30 duty.
Interrupting Rating See AIR.
Inverter (AC Drive) A term commonly used for an AC adjustable
frequency drive. An inverter is also a term used
to describe a particular section of an AC drive.
This section uses the DC voltage from a
previous stage (Intermediate DC Circuit) to
produce an AC current or voltage having the
desired frequency.
Inverter (UPS) This is the circuit in a UPS that converts DC
voltage from the battery into AC voltage for the
load.
IOC (Instantaneous Over-Current) IOC is a fault
condition that occurs when an excessive
amount of current passes through the drive.
This type of fault occurs when the current
exceeds the current rating of the drive by 250%
to 350%. Unlike an overload condition, IOC will
trip the drive instantaneously.
IPM (Intelligent Power Module) Module which
contains IGBT’s and “intelligent” switching
circuit. The IPM can be used as a self-contained
inverter.
IR Compensation A way to compensate for the voltage drop
across resistance of the AC or DC motor circuit
and the resultant reduction in speed. This
compensation also provides a way to improve
the speed regulation characteristics of the
motor, especially at low speeds. Drives that use
a tachometer-generator for speed feedback
generally do not require and IR compensation
circuit because the tachometer will inherently
compensate for the loss in speed.
Iron Loss See Core Loss.
Isolation Transformer A transformer that electrically separates the
drive from the AC power line. An isolation
transformer provides the following advantages:
1. In DC motor applications, it guards against
inadvertent grounding of plant power lines
through grounds in the DC motor armature
circuit.

2. Enhances protection of semiconductors from
line voltage transients.
3. Reduces disturbances from other solid state
control equipment such as drives without
isolation transformers, time clock systems,
electronic counters, etc.
Jogging Jogging is a means of accomplishing
momentary motor movement by repetitive
closure of a circuit using a single push-button or
contact element.
K Factor (power conditioning, transformers) Refers to specially designed transformers that
can withstand harsh harmonic currents,
particularly in the neutral conductor.
KVA or Volt-Ampere Output The KVA or volt-ampere rating designates the
output which a transformer can deliver for a
specified time at rated secondary voltage and
rated frequency without exceeding the specified
temperature rise (1KVA=1000-VA).
KVAR (kilovars) Reactive or non-working power provides the
magnetic flux necessary for the operation of the
device but is not transformed into any useful
work.
KW (kilowatts) Active or working power is the power which is
converted into useful work.
Kinetic Energy The energy of motion possessed by a body.
Limit Switch (motor control) This is one type of input device. It is a type of
sensor that is designed to detect physical
contact with an object.
Linear Acceleration/Deceleration (LAD) A circuit that controls the rate at which
the motor is allowed to accelerate to a set speed
or decelerate to zero speed. On most drives,
this circuit is adjustable and can be set to
accommodate a particular application.
Linearity A measure of how closely a characteristic
follows a straight line function.
Linear Loads The waveform of the current is the same as the
waveform of the voltage.
Liquid-Immersed Transformer (m.v. trans.) Transformer with core and coils immersed in
liquid (as opposed to a dry-type transformer).
Load (Mechanical) External resistance to movement that must be
overcome by a motor , under a given condition,
measured in the power required.

Load (electrical) An electrical path of varying resistance which
connects to the electrical system. Loads are any
device which uses electricity. For example,
appliances or lights.
Load Center A box for the distribution of electrical current
located either inside or outside the house which
connects to the service entrance conductors.
Often mistakenly called a “circuit breaker box”
or “fuse panel”. The proper name is a load
center.
Load (transformers) Expression of power in KVA or volt amperes-
supplied by the transformer.
Load Losses (transformers) See Winding Loss.
Locked-Rotor Current Steady state current taken from the line with the
rotor at standstill (at rated voltage and
frequency). This is the current when starting the
motor and load.
Locked-Rotor Torque The minimum torque that a motor will develop
at rest for all angular positions of the rotor (with
rated voltage applied at rated frequency).
Logic Devices They receive electrical signals from input
devices and make decisions based on preset
information. They then send electrical signals to
output devices. Examples of logic devices are
relays, timers and programmable logic
controllers.
Low power factor (I/R) When the non-working power is a large
component of the total power, such as lightly
loaded motors, the power factor could be .5 or
50%, which would be a ratio of 1/2 or 50%
power factor.
LRC (motor) Locked Rotor Current. This is the amount of
electrical current required to start and accelerate
a motor to its rated speed. Locked rotor current
may also be called locked rotor amps (LRA) or
inrush current. A motor’s LRC is used when
selecting motor overload protection devices.
Main Bus Bars Main conductors of electricity, which are inside
the load center, are composed of copper or
aluminum strips.
Main Circuit Breaker Switch which is connected to the main bus bars
that can disconnect power to the entire load
center.

Maximum Speed The setting on the drive which determines the
highest frequency that the drive will output.
Meggar Test A test used to measure an insulation system’s
resistance. This is usually measured in
megohms and tested by passing a high voltage
at low current through the motor windings and
measuring the resistance of the various
insulation systems.
Mid-Tap (transformers) A reduced-capacity tap midway in a winding -
usually the secondary.
Minimum Speed The setting on the drive which determines the
lowest frequency that the drive will output.
Motor Load The energy that a machine requires from a
motor in order to operate, measured in torque.
Motor Nameplate This plate is attached to each motor. It provides
motor information and specifications, such as
horsepower, full load current, service factor,
voltage and frequency, and the type of current.
The motor nameplate is a primary source for
information necessary to select control products.
Motor Overload This is a condition which exists when a motor
load increases above normal. The motor draws
more current in an attempt to produce more
energy to meet the increased motor load. The
additional current increases the temperature
inside the motor. Higher than normal
temperatures will cause damage to the motor.
Multispeed Motor An induction motor that can obtain two, three or
four discrete (fixed) speeds by the selection of
various stator winding configurations.
NEMA National Electrical Manufacturers Association.
The focus of NEMA is to establish voluntary
standards for its members to ensure that the
products they manufacture have general areas
of uniformity. NEMA produces more than 200
standards publications.
NEC The National Electrical Code is
recommendations of the National Fire
Protection Association and is revised every
three years. City or state regulations may differ
from code regulations and take precedence over
NEC rules.
Negative Feedback A condition where feedback is subtractive to the
input reference signal. Negative feedback forms
the basis for automatic control systems.

NEMA Class 1 (motor control centers) Independent units consisting of mechanical
groupings of combination motor control units,
feeder taps, and electrical devices arranged for
convenient assembly. Wiring is complete
between components within each unit.
Connections between units are not provided.
NEMA Class 2 (motor control centers) Interconnected units consisting of mechanical
groupings of combination motor control units,
feeder taps, and electrical devices arranged for
convenient assembly. Electrical interlocking and
wiring between units is provided. These
interconnections are completed as called out by
the purchaser.
NEMA Drilling (m.v. transformers) Prescribed hole pattern in spade terminals, lugs
and other connectors. Usually 1-3/4” on center
in square pattern for 4-hole, repetitive pattern
for six or more.
NEMA Type 1 Enclosure General Purpose. Primarily protects against
accidental contact with enclosed equipment.
Suitable for indoor use.
NEMA Type 12 Enclosure Indoor Dusttight and Driptight. Without
knockouts. Protects against liquids that are not
corrosive including oil and coolants. Often found
in an industrial environment.
NEMA Type 12K Enclosure Same as Type 12 but with knockouts in top and
bottom walls only.
NEMA Type 3 Enclosure Dusttight, Raintight. Protects against dust and
rain. Used outdoors. They are not sleet (ice)
proof. Applications include ship docks, subways,
and tunnels.
NEMA Type 3R Enclosure Rainproof, Sleet Resistant. Protects the normal
operation of the enclosed equipment from
interference due to rain, and resists equipment
damage due to sleet. For outdoor use in location
affected by rain and/or sleet.
NEMA Type 4 Enclosure Watertight. Protects against water interfering in
the operation of the enclosed equipment. The
enclosure may be used outdoors or in dairies or
other food preparation environments.
NEMA Type 4X Enclosure Watertight, Corrosion Resistant. Protection is
similar to NEMA Type 4 except Type 4X
enclosure is constructed of corrosion resistant
material. Used in fertilizer and chemical
manufacturing plants, meat packing plants
where environmental contaminants would
destroy the metal enclosure over time.

NEMA Type 5 Enclosure Indoor Dusttight. Intended for use indoors to
protect enclosed equipment against fibers and
flyings, lint, dust, and dirt.
NEMA Type 7 Enclosure Class 1, Group A, B, C and/or D. Indoor
Hazardous Locations. Protects against
explosions caused by electrical arcs that occur
during normal operation of motor control or
switching equipment. The enclosure is
constructed to prevent flammable gases or
vapors from entering the enclosure. Used in oil
refineries and natural gas plants. Do not decide
between NEMA Type 7 or NEMA Type 9 for
your customers. Let them tell you which
enclosure type will meet their requirements.
NEMA Type 9 Enclosure Similar to NEMA Type 7 except the enclosure
protects against environmental (airborne) dust.
Used in grain elevators and flour milling plants.
Do not decide between NEMA Type 7 or NEMA
Type 9 for your customers. Let them tell you
which enclosure type will meet their
requirements.
NEMA Type A (motor control centers) User field wiring connects directly to internal
device terminals in the unit and is provided only
on Class 1 Motor Control Centers.
NEMA Type B (motor control centers) User field control wiring connects directly to the
control unit terminal block(s) in or adjacent to
each unit and user field load wiring connects
directly to the device adjacent to the vertical
wireway.
NEMA Type C (motor control centers) User field control wiring on all units and load
wiring on Size 3 or smaller units connects
directly to master terminal blocks mounted at
the top and bottom of those vertical sections
containing control units. Control wiring on all
units and load wiring on Size 3 or smaller units
are factory wired to their mater terminal block.
User field load wiring for Size 4 or larger units
connects directly to the device terminals.
NFPA National Fire Protection Association. This
association has developed a set of minimum
standards for electrical installations in home,
commercial and industrial environments, called
the National Electrical Code (NEC). Although
the NEC is nationally accepted in the industry, it
standards are subject to interpretation by local
authorities. Each town, city, county or state may
establish codes to govern the installation of
electrical equipment or wiring.

Noise (power conditioning) Unwanted electrical signals which produce
undesirable effects in circuits in which they
occur.
No-Load Loss See Core Loss.
Offset The steady state deviation of a controlled
variable from a fixed setpoint.
Oil Resistant Gaskets Gaskets (used in an enclosure) that are made of
those materials which resist oil or oil fumes.
Oiltight "Oiltight" means that a device is so constructed
or protected as to exclude oils, coolants, and
similar liquids under specified test conditions.
One Line Diagram A simplified wiring diagram with a single line
representing all the conductors and symbols
representing the elements of the system.
Open Loop A control system that lacks feedback.
OP Amp An Operational Amplifier is usually a high-gain
DC amplifier that is designed to be used with
external circuit elements.
Open Machine (Motors) A machine having ventilating openings which
permit passage of external cooling air over and
around the windings of the machine.
A. Dripproof Machine is an open type machine
in which ventilating openings are so
constructed that successful operation is not
interfered with when drops of liquid or solid
particles strike or enter the enclosure at any
angle from 0 to 15 degrees downward from
vertical.
B. Splashproof Machine is an open type
machine in which ventilating openings are so
constructed that successful operation is not
interfered with when drops of liquid or solid
particles strike or enter the enclosure at any
angle not greater than 100 degrees
downward from the vertical.
C. Semiguarded Machine is an open machine in
which part of the ventilating openings in the
machine, normally the top half, are guarded
as in the case of a “guarded machine” but the
others are left open.

D. Guarded Machine (NEMA Standard) is an
open machine in which all openings giving
direct access to live metal or rotating parts
(except smooth rotating surfaces) are limited
in size by the structural parts or by the
screens, baffles, grilles, expanded metal or
other means to prevent accidental contact
with hazardous parts. Openings giving direct
access to such live or rotating parts shall not
permit the passage of a cylindrical rod 0.75
inch in diameter.
E. Dripproof Guarded Machine is a dripproof
machine whose ventilating openings are
guarded in accordance with the definition of
a guarded machine.
F. Open Externally Ventilated Machine is one
which is ventilated by means of a separate
motor driven blower mounted on the machine
enclosure. This machine is sometimes known
as a blower-ventilated or a force-ventilated
machine.
G. Open Pipe Ventilated Machine is basically an
open machine except that openings for
admission of ventilating air are so arranged
that inlet ducts or pipes can be connected to
them. Air may be circulated by means
integral with the machine or by means
external to the machine (separately or forced
ventilated).
H. Weather-Protected Machine is an open
enclosure divided into two types:
1. Type 1 enclosures have ventilating
passages constructed to minimize the
entrance of rain, snow, airborne particles
and prevent passage of a 0.75 inch
diameter cylindrical rod.
2. Type 2 enclosures provide additional
protection through the design of their
intake and exhaust ventilating passages.
The passages are so arranged that wind
and airborne particles blown into the
machine can be discharged without
entering directly into the electrical parts of
the machine. Additional baffling is
provided to minimize the possibility of
moisture or dirt being carried inside the
machine.

Operating/Service Deviation A means of specifying the speed regulating
performance of a drive controller generally in
percent of base speed.
Operating Deviation Defines speed change due to load change and
typically assumes:
1. A change from one steady state load value to
another (not transient).
2. A 95% maximum load change.
Service Deviation Defines speed change due to changes in
ambient conditions greater than these typical
variations:
Condition Change
AC Line Voltage ± 10%
AC Line Frequency ± 3%
Ambient Temperature 15° C
Output Devices They receive electrical signals from logic
devices. Two examples of output devices are
contactors and starters.
Overcurrent (circuit breakers) Any current in excess of the rated current of
equipment or the ampacity of a conductor.
Overcurrent Condition Excessive circuit current which could damage
equipment connected to the circuit. Typically a
circuit breaker is designed to sense overcurrent
conditions. When it does the breaker opens the
electrical path protecting the connected
equipment from being damaged by excessive
current. When this happen the circuit breaker is
said to have “tripped”. When the situation that
caused an overcurrent has been corrected,
power can be restored to the circuit. This is
done by moving the circuit breaker handle from
its trip position to the “off” position to reset it.
Then the handle can be moved to the “on”
position.
Overload Capacity The ability of the drive to withstand currents
beyond the systems continuous rating. It is
normally specified as a percentage of full load
current for a specified time period. Overload
capacity is defined by NEMA as 150% of rated
full load current for one minute for Standard
Industrial DC Motors.
Overshoot The amount that a controlled variable exceeds
desired value after a change of input.

Overvoltage Overvoltage is a fault condition that occurs
when the input voltage to the drive exceeds the
trip value. Overvoltage is not a parameter that
can be adjusted.
Panelboards A single panel or group of panel units designed
for assembly in the form of a single panel;
including buses, automatic overcurrent devices,
and equipped with or without switches for the
control of light, heat, or power circuits; designed
to be placed in a cabinet or cutout box placed in
or against a wall or partition and accessible only
from the front.
Phase (∅, or PH) One of three streams of current which is
produced by a generator. Each phase of current
flows from a generator in a separate conductor.
Phases(electrical service) Single phase or polyphase, which is normally
three phases.
Plugging Plugging refers to a type of motor braking
provided by reversing either line voltage polarity
or phase sequence so that the motor develops a
counter-torque which exerts a retarding force to
brake the motor.
Plug-on Connection Describes how an interior device is connected to
a vertical bus.
Poke Thru Fittings (wire mgmt.) A flexible and inexpensive method of providing
power receptacles, computer access, and
telecommunications services in an existing
facility.
Position Transducer An electronic device (e.g. encoder or resolver)
that measures actual position and converts this
measurement into a feedback signal convenient
for transmission. This signal may then be used
as an input to a programmable logic controller
which controls the parameters of the positioning
system.
Positive Feedback Positive feedback is a condition where the
feedback is additive to the input signal.
Power Work done per unit of time. Measured in HP or
watts: 1 HP = 33,000 ft-lb/min = 746 watts
Power factor The ratio of active power to total power. Power
factor can be expressed as percentage or as a
raw number. For example, .80 or 80%. If active
power equals total power, the power factor of
the load would be 1 or 2 or 100%. This is the
highest power factor possible.

Preset Speed Preset speed refers to one or more fixed speeds
at which the drive will operate.
Primary Taps (transformers) Taps added in the primary winding
Proof (Used as a suffix) "Proof" means a device is constructed,
protected, or treated so that successful
operation of the apparatus is not interfered with
when subjected to the specified material or
condition. Such as "rainproof."
Pull-In Torque (Synchronous Motors) The maximum constant
torque which a synchronous motor will
accelerate into synchronism at rated voltage
and frequency.
Pull-Out Torque (Synchronous Motors) The maximum running
torque of a synchronous motor.
Pull-Up Torque The torque required to accelerate the load from
standstill to full speed (where breakdown torque
occurs), expressed in percent of running torque.
It is the torque required not only to overcome
friction, windage and product loading but also to
overcome the inertia of the machine. The torque
required by a machine may not be constant
after the machine has started to turn. This load
type is characteristic of fans, centrifugal pumps
and certain machine tools.
Pushbuttons (motor control) Devices which are activated manually by a
person.
Pulse Width Modulation (PWM) A type of AC adjustable frequency drive that
accomplishes frequency and voltage control at
the output section (inverter) of the drive. The
drive’s output voltage is always a constant
amplitude and by “chopping” (pulse width
modulating) the average voltage is controlled.
Radial Feed (m.v. transformers) Incoming HV cables end at this transformer in a
single set of HV bushings.
Rainproof "Rainproof" means an apparatus is so
constructed, protected, or treated as to prevent
rain, under specified test conditions, from
interfering with successful operation of the
apparatus.
Raintight "Raintight" means that a device is so
constructed or protected as to exclude rain
under specified test conditions.

Reactance Any force that opposes changes in current or
voltage. The inertia of electrons causes them to
oppose sudden changes in current flow or
voltage.
Rectifier A device that transforms alternating current into
direct current.
Regeneration A characteristic of a motor to act as a generator
when the CEMF is larger than the drive’s
applied voltage (DC drives) or when the rotor
synchronous frequency is greater than the
applied frequency (AC drives).
Regenerative Braking The technique of slowing or stopping a drive by
regeneration. See also Braking.
Regenerative Control A regenerative drive contains the inherent
capability and/or power semi-conductors to
control the flow of power to and from the motor.
Regulation The ability of a control system to hold a speed
once it has been set. Regulation is given in
percentages of either base speed or set speed.
Regulation is rated upon two separate sets of
conditions:
A. Load Regulation (speed regulating) is the
percentage of speed change with a defined
change in load, assuming all other
parameters to be constant. Speed regulation
values of 2% are possible in drives utilizing
armature voltage feedback, while regulation
of 0.01% is possible using digital regulator
schemes.
B. Line Regulation is the percentage of speed
change with a given line voltage change,
assuming all other parameters to be
constant.
Relay Section (motor control centers) Includes a full height, full width removable panel
with a 72" hinged door to provide space for
customer devices in a Motor Control Center.
Remote Main Main disconnect device is outside the
panelboard.
Resistance (represented as an “R”): This is the property that prevents electrons from
moving. Sometimes it is referred to as a “load”.
Resistance is measured in ohms.

Resistant (Used as suffix) "Resistant" means that a device is constructed,
protected, or treated so that it will not be
damaged when subjected to the specified
material or conditions for a specified period of
time. Such as "sleet resistant."
Resolution The smallest distinguishable increment into
which a quantity can be divided (e.g. position or
shaft speed). It is also the degree to which
nearly equal values of a quantity can be
discriminated. For encoders, it is the number of
unique electrically identified positions occurring
in 360 degrees of input shaft rotation.
Reversing Changing direction of rotation of the motor
armature or rotor. A DC motor is reversed by
changing the polarity of the field or the
armature, but not both. An AC motor is reversed
by reversing the connections of one leg on the
three phase power line. The reversing function
can be performed in one of the following ways:
A. (DC) Contactor Reversing is done by
changing the phase rotation of an AC motor
or the polarity to a DC motor armature with
switching contactors. The contactors are
operated by momentary push buttons, and/or
limit switches to stop the motor and change
directions. A zero speed (anti-plugging)
circuit is associated with this system to
protect the motor and control.
B. (DC) Field Reversing is accomplished by
changing the DC polarity to the motor shunt
field. This type of reversing can be
accomplished with DC rated contactors or by
means of an electrically controlled solid state
field supply.
C. (DC) Manual Reversing is the act of
reversing the DC polarity to the motor
armature by changing the position of a single
switch. The switch is usually detented to give
a degree of mechanical anti-plugging
protection. Limit switches and remote
stations cannot be used with this system.
Dynamic braking is recommended.
D. (AC or DC) Static Reversing is the act of
reversing the DC polarity of the DC motor
armature or phase rotation of an AC motor
with no mechanical switching. This is
accomplished electronically with solid state
devices. Solid state anti-plugging circuitry is
generally a part of the design.

RMS Root Mean Square
Rotor (motor) A rotating iron core with wire windings. The rotor
is attached to the shaft.
Sensors (motor control) Devices which are activated when they detect
conditions such as the presence of a metal, the
pressure of a liquid or gas, or the position of an
object.
Series Connected System A system consisting of a combination of two
overcurrent protective devices connected in
series. The lineside (main) device must have an
interrupting rating equal to or greater than the
available fault current at the lineside terminals
of the device. The loadside (branch) breaker
has a lower interrupting rating. The series rated
combinations are based on actual UL testing.
Service Deviation See Operating/Service Deviation
Service Drop Conductors Electrical wires from the power lines which
attach to a house.
Service Entrance The place where the electric supply from the
utility company enters a building.
Service Entrance Conductors Conductors which are extended from the watt-
hour meter to the house.
Service Factor (motor) This defines a margin of safety that allows for
those times when motors might be operated
above their rated horsepower. This service
factor protects the motor against damage that
might be caused by the occasional excessive
load.
When used on a motor nameplate, a number
which indicates how much above the nameplate
rating a motor can be loaded without causing
serious degradation (i.e., a motor with 1.5 S-F
can produce 15% greater torque than one with
1.0 S-F.) When used in applying motors or
gearmotors, it is a figure of merit which is used
to adjust measured loads in an attempt to
compensate for conditions which are difficult to
measure or define.
Service Fittings (wire mgmt.) Sometimes known as "activation units" access
the duct system to provide power, computer
access, and telecommunications services in an
existing facility.
Set Speed The desired operating speed.

Shaft (motor) A metal rod mounted in the case using bearing
assemblies that allow the shaft to turn (rotate).
Shipping Splits (motor control centers) Motor Control Centers are shipped in more than
one container to ease in handling.
Short Circuit Current Ratings (SCCR) SCCR are used to select end-use equipment for
specific available fault current applications. This
maximum current rating applies only to end-use
equipment such as switchboards, panelboards
and motor control centers. The SCCR covers
not only the overcurrent protective device in the
end-use equipment, but also the overall
construction of the equipment i.e. it is an
integrated equipment rating.
Shock Load The load seen by a clutch, brake or motor in a
system which transmits high peak loads. This
type of load is present in crushers, separators,
grinders, conveyors, winches, and cranes
Silicon Controlled Rectifier (SCR) A solid state switch, sometimes referred
to as a thyristor. The SCR has an anode,
cathode and control element called a gate.
SCR’s are turned on by a voltage pulse applied
between the gate and cathode. They are turned
off when the current between the cathode and
anode reaches zero. The device provides
controlled rectification since it can be turned on
at will. The SCR can rapidly switch large
currents at high voltages. They are small in size
and low in weight.
Sinewave (UPS) This describes the shape of the output wave
from the inverter. A sinewave is the same shape
as that supplied from the utility.
Single phase voltage system A single phase voltage system can supply 120
volts or 240 volts. The system uses three wires,
two “hot” (carrying current) and one neutral wire
Skew The arrangement of laminations on a rotor or
armature to provide a slight angular pattern of
their slots with respect to the shaft axis. This
pattern helps to eliminate low speed cogging in
an armature and minimize induced vibration in a
rotor as well as reduce associated noise.
Skewing Refers to time delay or offset between any two
signals in relation to each other.
Sleet Resistant "Sleet Resistant" means that an apparatus is so
constructed that accumulation and melting of
sleet (ice), under specified conditions, will not
damage the apparatus.

Sleetproof "Sleetproof" means that a device is so
constructed or protected that the accumulation
of sleet (ice), under specified conditions, will not
interfere with the successful operation of the
apparatus, including the external operating
mechanism.
Slewing Slewing is an incremental motion of the motor
shaft or machine table from one position to
another at maximum speed without losing
position control.
Slip The difference between rotating magnetic field
speed (synchronous speed) and rotor speed of
AC induction motors. Usually expressed as a
percentage of synchronous speed.
Slip Compensation Method of increasing the output frequency to
maintain motor speed as the load on the motor
increases
Spade Bushing (m.v. transformers) Bushings with flattened surface on which cable
lugs can be bolted.
Special Purpose Motor A motor with special operating characteristics or
special mechanical construction or both,
designed for a particular application and not
falling within the definition of a general purpose
or definite purpose motor (NEMA).
Speed Range The speed minimum and maximum at which a
motor must operate under constant or variable
torque load conditions. A 50:1 speed range for a
motor with top speed of 1800 RPM means the
motor must operate as low as 36 RPM and still
remain within regulation specifications.
Controllers are capable of wider controllable
speed ranges than motors because there is no
thermal limitation, only electrical. Controllable
speed range of a motor is limited by the ability
to deliver 100% torque below base speed
without additional cooling.
Speed Regulation The numerical measure in percent, of how
accurately the motor speed can be maintained.
It is the percentage of change in speed between
full load and no load.
Split Bus Panelboard A panelboard with two or three sets of isolated
bus bars mounted in the same interior.
Squarewave (UPS) This is a poor manifestation of a sinewave. This
is found on economy models of UPS. This may
not be beneficial to most electronic loads.

Squirrel Cage AC Motor Most commonly used motor in industry and in
the home.
Stability The ability of a drive to operate a motor at
constant speed (under varying load), without
“hunting” (alternatively speeding up and slowing
down). It is related to both the characteristics of
the load being driven and electrical time
constants in the drive regulator circuits.
Stator (motor) A stationary iron core with wire windings. The
stator is attached to the case.
Steppedwave (UPS) This waveform combines the benefits of a
sinewave with the cost advantages of a
squarewave device. This is acceptable to the
majority of electronic loads.
Stiffness The ability of a device to resist deviation due to
load change.
Surge Protection The process of absorbing and clipping voltage
transients on an incoming AC line or control
circuit. MOVs (Metal Oxide Varistors) and
specially designed R-C networks are usually
used to accomplish this.
Synchronous Speed The speed of an AC induction motor’s rotating
magnetic field. It is determined by the frequency
applied to the stator and the number of
magnetic poles present in each phase of the
stator windings. Mathematically, it is expressed
as:
Sync Speed (RPM) = 120 X Applied Freq.
(Hz)/Number of poles per phase.
Tachometer-Generator (Tach) A small generator normally used as a rotational
speed sensing device. Tachometers are
typically coupled to the shaft of DC or AC
motors requiring close speed regulation. The
tach feeds a signal to a controller which then
adjusts the output voltage or frequency to the
motor.
Tap (transformers) Connection brought out of a winding at some
point between its extremities, usually to permit
changing the voltage or current ratio.
Thread Speed A fixed low speed, usually adjustable, supplied
to provide a convenient method for loading and
threading machines. May also be called a preset
speed.

Three Phase Voltage System Provides three “hot” wires for the customer’s
use. The three phase voltage system has two
configurations, wye and delta.
Throat (m.v. transformers) Extension of the cabinet or enclosure that
surrounds bushings or cable connections. Used
for joining a transformer to adjacent switchgear,
busway, etc. Usually rectangular and fitted with
a flange for bolting to the connected gear.
Tight (Used as a suffix) "Tight" means that an enclosure is so
constructed that it will exclude the specified
material under specified conditions.
Torque (motor) A turning force applied to a shaft, tending to
cause rotation. Torque is normally measured in
ounce-inches or pound-feet and is equal to the
force applied, times the radius through which it
acts
Torque Constant (in-lbs) This motor parameter provides a
relationship between input current and output
torque. For each ampere of current applied to
the rotor, a fixed amount of torque will result.
Torque Control A method of using current limiting circuitry to
regulate torque instead of speed.
Totally Enclosed Machine (Motor) A totally enclosed machine is one so enclosed
as to prevent the free exchange of air between
the inside and the outside of the case. It is not
sufficiently enclosed to be termed air-tight.
A. Totally Enclosed Fan-Cooled is a totally
enclosed machine equipped for exterior
cooling by means of a fan or fans integral
with the machine but external to the
enclosing parts.
B. Explosionproof Machine is a totally enclosed
machine whose enclosure is designed and
constructed to withstand an explosion of a
specified gas or vapor which may occur
within it and to prevent the ignition of the
specified gas or vapor surrounding the
machine by sparks, flashes, or explosions of
the specified gas or vapor which may occur
within the machine casing.

C. Dust-Ignition-Proof Machine is a totally
enclosed machine whose enclosure is
designed and constructed in a manner which
will exclude ignitable amounts of dust or
amounts which might affect performance or
rating, and which will not permit arcs, sparks
or heat otherwise generated or liberated
inside of the enclosure to cause ignition of
exterior accumulations or atmospheric
suspensions of a specific dust on or in the
vicinity of the enclosure.
D. Waterproof Machine is a totally enclosed
machine so constructed that it will exclude
water applied in the form of a stream from a
hose, except that leakage may occur around
the shaft provided it is prevented from
entering the oil reservoir and provision is
made for automatically draining the machine.
The means for automatic draining may be a
check valve or a tapped hole at the lowest
part of the frame which will serve for
application of a drain pipe.
E. Totally Enclosed Water-Cooled Machine is a
totally enclosed machine which is cooled by
circulating water, the water or water
conductors coming in direct contact with the
machine parts.
F. Totally Enclosed Water-Air-Cooled Machine
is a totally enclosed machine which is cooled
by circulating air which, in turn, is cooled by
circulating water. It is provided with a water-
cooled heat exchanger for cooling the interior
air and a fan or fans, integral with the rotor
shaft or separate, for circulating the internal
air.
G. Totally Enclosed Air-to-Air Cooled Machine is
a totally enclosed machine which is cooled
by circulating the internal air through a heat
exchanger which, in turn, is cooled by
circulating external air. It is provided with an
air to air heat exchanger for cooling the
internal air and a fan or fans, integral with the
rotor or separate, for circulating the internal
air and a separate fan for circulating the
external air.

H. Totally Enclosed Fan-Cooled Guarded
Machine is a totally enclosed fan-cooled
machine in which all openings giving direct
access to the fan are limited in size by the
design of the structural parts or by screens,
grilles, expanded metal, etc., to prevent
accidental contact with the fan. Such
openings shall not permit the passage of a
cylindrical rod 0.75 inch in diameter, and a
probe shall not contact the blades, spokes or
other irregular surfaces of the fan.
I. Totally enclosed Air-Over Machine is a totally
enclosed machine intended for exterior
cooling by a ventilating means external to the
machine.
Transducer A device that converts one energy form to
another (e.g., mechanical to electrical). Also a
device that when actuated by signals from one
or more systems or media, can supply related
signals to one or more other systems or media.
Transfer Time (UPS) The time it takes for a UPS to “Cut over” from
utility power to battery power.
Transformers The purpose of a transformer is to change the
voltage from one level to another. A transformer
is composed of three parts: a coil, the primary
winding and the secondary winding. “Windings”
consist of coils of wire wrapped around the core
(which can be made out of iron or metal). If an
electrical current is passed through a wire
wrapped around a piece of iron/metal, the
iron/metal will become magnetized. A magnetic
field is created. This illustrates the
electromagnetic principle. In a transformer, the
electromagnetic principle works as follows:
power is fed into the primary winding. The
electrical current being fed into the primary
winding is transformed into magnetic energy.
The core then carries the magnetic energy to
the secondary winding. Working in reverse, the
secondary winding transforms the magnetic
energy back into electrical energy. It is the turns
in the transformer that give specific primary and
secondary voltages.
Transformer Regulation The percentage difference between voltage at
the secondary terminals under no-load condition
versus voltage under full-load. This value
depends on the load power factor and is usually
reported at 1.0 PF and 0.8 PF.
Transient A momentary deviation in an electrical or
mechanical system

Transistor A solid state three-terminal device that allows
amplification of signals and can be used for
switching and control. The three terminals are
called the emitter, base and collector.
Transmission lines Transmission lines carry, or transmit, electricity
to homes and businesses.
Transmission Networks Method by which power plants deliver generated
electricity to their customers. Utility companies
transmit electrical power at high voltage levels,
sometimes as high as 750,000 volts (750kV)
because it is less expensive. Power transmitted
at high voltage has lower current, and lower
current permits the use of a smaller conductor
or wire. Operating voltages used in resident,
commercial and industrial settings are between
120 volts and 600 volts.
Transverse Mode Noise (power conditioning) This is electrical interference that occurs
between hot and neutral.
Trench Duct (wire mgmt.) A flush floor wire management system.
Turbines Machines which drive generators. Turbines are
powered by various sources of energy, such as
water, coal or nuclear energy.
Underfloor Duct (wire mgmt.) A concrete encased single compartment or
multi-compartment duct system providing
distribution and access to power and
telecommunications wiring.
Undervoltage A fault condition that occurs when the input
voltage to the drive is below the trip value.
Undervoltage is not a parameter that can be
adjusted.
UL Underwriters Laboratories. This is a non-profit
corporation that establishes safety and
performance standards for electrical products
and lists products that meet these standards.
Manufacturers who want UL listing make
application to UL to list their products. These
products are evaluated by a highly-trained
technical staff who uses state of the art
equipment to determine whether products
comply with UL standards. UL also has a
network of inspectors who make periodic and
unannounced visits to factories. There they
check compliance with UL standards in the
production of electrical equipment that bears the
UL label.
Utility Companies Supply electricity using power lines.

Variable Volts/Hertz When the output volts varies at a different rate
than the rate at which the output frequency
varies. Variable Volts/Hertz is sometimes
desired to decrease motor noise and reduce
motor core losses.
Vector A quantity that has magnitude, direction and
sense. This quantity is commonly represented
by a directed line segment whose length
represents the magnitude and whose orientation
in space represents the direction.
Voltage (represented as an “E”) The force or “push” needed to move the
electrons. Voltage can also be thought of as the
difference of force or potential between two
points. Voltage is measured in volts.
Voltage Boost Increasing the Volts/Hertz ratio of drives at low
speeds to compensate for resistance losses in
the motor core. This compensation allows the
motor to develop rated torque at low speeds.
Voltage Regulation The voltage drop that will occur in the
transformer under full load as a percentage of
the open circuit voltage rating of the winding.
Varies with load and power-factor of the load-
.1% to 10% might be outside limits of normal
range.
Voltage Regulation (power conditioning) This is a measurement of a voltage stabilizers
ability to hold its output close to the nominal
rating despite a fluctuating input. This is
normally expressed as a +/- percentage.
VPI (m.v. transformer) Vacuum Pressure Impregnation. A
manufacturing process whereby the coils of a
transformer are impregnated with varnish, resin
or other process fluid by use of both a vacuum
and pressure cycle.
VVI A type of AC adjustable frequency drive that
controls the voltage and frequency to the motor
to produce variable speed operation. A VVI type
drive controls the voltage in a section other than
the output section where frequency generation
takes place. The frequency control is
accomplished by an output bridge circuit which
switches the variable voltage to the motor at the
desired frequency.
Wall Duct (wire mgmt.) A steel-enclosed wall or ceiling lay-in duct
system (raceway). Wall duct is UL listed for
enclosure of wiring for medical diagnostic
equipment.

Watertight "Watertight" means that a device is so
constructed as to exclude water applied in the
form of a hose stream, under specified test
conditions.
Watthour Meter Meter mounted on the outside of a house and
attached to service drop conductors. This meter
measures the amount of electricity used in the
house.
Winding Loss (transformers) The losses, principally I
2
R loss in the winding of
the transformer, expressed in watts or KW.
Winding losses vary with the square of the load.
Wireway Sheet metal troughs with hinged or removable
covers for housing and protecting electric wires
and cable and in which conductors are laid in
place after the wireway has been installed.
Withstand Rating (circuit breakers) This is the level of RMS symmetrical current
that a circuit breaker can carry with the contacts
in the closed position for a maximum of 30
cycles, typically.
Work A force moving an object over a distance.
Measured in inch-ounces (in-oz) or foot-pounds
(ft-lbs). Work = Force X Distance.
Wye Connection A standard three-wire transformer connection
with similar ends of the single-phase coils
connected. This common point forms the
electrical neutral point and may be grounded.
Wye Voltage System This provides all three phases of current carried
by three “hot” wires and one neutral wire.
Sometimes it is called a 3 phase 4 wire system.
The wye voltage system is the most commonly
used three phase voltage system.
X Axis The axis of motion that is always horizontal and
parallel to the work holding surface.
Y Axis The axis of motion that is perpendicular to both
the X and Z axes.
Z Axis The axis of motion that is always parallel to the
principle spindle of the machine.

Introduction to AC Drives Final Test
FINAL TEST

Final Test Final Test
INTRODUCTION TO AC DRIVES FINAL TEST
INSTRUCTIONS FOR COMPLETING AND RETURNING SCANNABLE ANSWER SHEETS
Using Scannable Answer Sheets (Please follow the directions to ensure correct scoring of the
final test):
• You will be recording your multiple choice answers on a scannable answer sheet. Mark your
answer sheet with either a #2 pencil or a blue or back ball point pen. Do not make any stray
marks or modifications to the answer sheet.
• Do not photocopy or fax the answer sheets - The original answer sheet must be returned
• If you need additional answer sheets, please call Organizational Development and Education
at: 847-925-3700.
Completing the Answer Sheet (Side 1):
• Name: Complete the name grid by printing your last name, first name, and middle initial in
the proper spaces, printing one letter in each box. Next, fill in the circle corresponding to
each letter in the column below.
• Field Office Location: Print the number of the field office where you are located, printing one
number in each box. Next, fill in the circle corresponding to each letter in the column below.
• Identification Number: In the box labeled “Identification Number,” write your social security
number without skipping any spaces. Next, fill in the circle corresponding to each number in
the column below.
• Sex and Grade or Education: Leave SEX and GRADE or EDUCATION blank.
• Questions: For each question, you are to fill in the circle containing the letter which
corresponds to the best answer. Only one answer is acceptable for each question. Make sure
that the number of the question corresponds to the number on the answer sheet.
Returning Answer Sheets For Scoring:
All completed answer sheets are to be mailed to:
Attention: Nancy Duncan
Organizational Development & Education
1100 Woodfield Road
Suite 430
Schaumburg, IL 60173

1. The margin of safety whereby a motor can be occasionally operated either intentionally or
unintentionally above its rated horsepower is called:
A. Motor overload
B. Motor slip
C. Motor time rating
D. Motor service factor
2. The torque vs speed relationship is:
A. When torque increases speed also increases
B. When torque increases speed decreases
C. When torque decreases frequency decreases
D. When torque decreases current increases
3. All Square D AC Drives:
A. Use pulse width modulation
B. Control motor speed by varying the motor current
C. Require feedback devices to adjust speed
D. Use an inverter to change 60 Hz constant frequency AC to DC
4. Dynamic braking is when a resistor is used to dissipate the energy being created when the
motor starts to act like a generator.
A. True
B. False
5. Whenever AC drives are used to control a motor it means that the speed of the motor is
going to be changed. Generally speaking, less speed means less motor cooling.
A. True
B. False
6. A NEMA Design B motor:
A. Is an excellent choice for applications of high inertia loads
B. Has a very high slip range
C. Is an excellent choice for variable torque applications
D. Has a very high locked rotor torque capability

7. Torque is related to current
A. True
B. False
8. Locked rotor amps (LRA) is:
A. The current flow required by a motor during normal operation to produce its designated
horsepower
B. The current dissipated through the dynamic braking resistors.
C. The current applied from the electrical distribution system to the motor.
D. The current required by the motor in order for it to start.
9. The synchronous speed of an AC induction motor is determined by the frequency applied to
the motor’s rotor.
A. True
B. False
10. Examples of constant torque loads would be: conveyors, hoists, drill presses and positive
displacement pumps.
A. True
B. False
11. The effects that reduced speed control has on a constant torque fan or pump are
summarized by a set of rules know as the Affinity Laws.
A. True
B. False
12. Which is NOT a benefit of AC drives:
A. Energy savings, particularly on fans and pumps
B. Standard AC motors can be used
C. Reduced wear and tear on machinery
D. Low initial investment
13. The most widely used type of motor is the:
A. Direct current
B. Synchronous
C. Wound rotor induction
D. Squirrel cage induction
14. A soft start device reduces voltage and current at startup to relieve stress on the motor and
machinery.
A. True
B. False

15. OMEGAPAK Class 8804 Type PT family of AC drives offers:
A. Reliable, cost-effective speed control for low horsepower, standard three-phase AC
induction motors.
B. Reliable, cost-effective speed control for high horsepower, standard three-phase AC
induction motors.
C. Reliable control for low horsepower, standard single-phase AC induction motors.
D. Speed control for standard AC induction motors.
16. The ALTIVAR 66 drives were developed as a:
A. Temporary product
B. Domestic product
C. Global product
D. Product for export only
17. The ALTIVAR 16 drive has rated power size ranges from:
A. 1/2 to 3 Hp (200-240V AC) and 1 to 5 Hp (400-460V AC)
B. 1 to 5 Hp (120-240V AC) and 10 to 75 Hp (400-460V AC)
C. 3 to 30 Hp (200-240V AC) and 10 to 500 Hp (400-460V AC)
D. 1/2 to 1 1/3 Hp (120V AC) and 5 to 25 Hp (400-460V AC)
18. The ALTIVAR 16 stopping methods are:
A. Freewheel, ramp to S ramp, brake control
B. Freewheel, ramp to stop, brake control
C. Freewheel, ramp to stop, DC injection control
D. Across-the-line stopping, mechanical braking
19. The ALTIVAR 66 horsepower range goes from:
A. 1 to 10 HP variable torque
B. 3 to 150 HP constant torque
C. 1 to 350 HP constant torque
D. 3 to 350 HP constant torque
20. When the ALTIVAR 66 arrives at the user’s location the drive is set up for:
A. Operation with average performance and no factory made adjustments
B. Operation with optimized performance and no factory made adjustments
C. Operation with optimized performance and some factory made adjustments
D. Operation with average performance and some factory made adjustments
21. Communications can be connected to the ALTIVAR 66 through which of the following
methods:
A. B1 extension module
B. B1 or B2 extension module
C. Communication card carrier module
D. B1 or B2 extension module or communication card carrier module

22. The ALTIVAR 18 was designed for the OEM market.
A. True
B. False
23. MCC’s are manufactured at the _____.
24. MCC with ALTIVAR 66 drives are available at this time in NEMA:
A. Type 1 and Type 12 enclosures only
B. Type 1, Type 1 Gasketed enclosures, and Type 12 only
C. Type 4, Type 4R and Type 12 enclosures only
D. Type 1 only
25. When taking an order for an open type replacement drive, it is important to know the
dimensions of the allotted drive space.
A. True
B. False
26. Square D’s method for controlling the temperature inside the MCC cabinet is called:
A. Convection Cooling
B. Cooling Management System
C. Thermal Management System
D. Thermal Guard Management System
27. The cooling system maintains the drive’s working temperature by:
A. Circulating air across the heat sink of the drive itself
B. Circulating outside air through the cabinet
C. Circulating air conditioned air through the cabinet
D. Circulating inside air around in the cabinet
28. If a user does not have a Square D name plate and designator on the front door of the
cabinet, the replacement drive type would be considered:
A. Enclosed type
B. MCC type
C. Open type
29. If the dimensions of the new drive are larger than the original drive, ____ may be required
for additional space.
A. Unit extenders
B. Special enclosure doors
C. Split drives
D. A whole new enclosure

30. Where and what should you have the user look for when working with a MCC?
A. On the back of the front door for the Class and Type number
B. Inside the drive’s bucket for the data plate and locate the plant code and the Factory
Order Number
C. Inside the drive’s bucket on the drive itself for the data plate and locate the plant code
and the Factory Order Number
D. On the back of the MCC cabinet for the data plate and locate the plant code and the
Factory Order Number
31. When identifying a replacement drive for an existing installation that is not in a Square D
enclosure:
A. Ask the customer for motor nameplate data
B. Ask the customer for class/or product number from the nameplate on the drive
C. Ask the customer for the class or product number from the enclosure data plate
D. Call the local Square D Sales Office right away
32. Square D’s thermal management system:
A. Eliminates “hot spot” problems
B. Reduces environmental contaminates around the drive
C. Eliminates restrictions on drive placement in the MCC structure
D. All of the above

Basics of ac drives

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