Three phase induction motor – construction, operation & application..ppt

Sanjivani Rural Education Society’s
Sanjivani K. B. P. Polytechnic, Kopargaon-423603
With NBA ACCREDIATED programs , Approved by AICTE, New Delhi,
Recognized by Govt. of Maharashtra, Affiliated to Maharashtra State Board of Technical Education, Mumbai,
ISO 9001:2015 Certified Institute
Department of Mechatronics
Prof. S. C. Bhangale
Lecturer
E-mail : bhangalesonaletc@sanjivani.org.in
Contact No: 7745801978
Subject :- Electrical Engineering
Second Year Mechatronics
Unit 4 - AC MACHINES

Content
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Department Of Mechatronics, Sanjivani K. B. P.Polytechnic, Kopargaon Prof. S.C.Bhangale
4.1 Three phase Induction Motor – construction,
operation & application.

Introduction
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• The motor which operates on AC supply are called as AC motor. Induction
motors operates on AC supply, i.e., alternating current supplied directly to
the stator winding & by induction or transformer action, to the rotor
winding. Hence this type of motor is called as induction motors.
• In fact the induction motor can be considered as a rotating transformer, i.e.,
stationary winding on stator is connected to the AC supply , while the
other winding mounted on a rotor receives its power by transformer action
while it rotates.

Construction of Three phase Induction Motor
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Main parts:
1. Stator:
• As the name suggest it is the stationary part of the motor, laminated
electromagnetic core with slots to accommodate 3 phase insulated
windings spaced 1200 apart in space.
• Stator core housed in standard sized frames.
• The frame has terminal box for the windings.
• Stator Windings may be star or delta connected.
• The function of the stator winding is to produce a rotating magnetic field
in the air gap between stator & rotor..

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2. Rotor:
• Laminated construction with slots to house conductor bars in squirrel cage
rotors and windings in slip ring rotors.
• Mounted on steel shaft supported by bearings housed in the end covers.
• Slip rings provided to connect to the rotor windings in wound rotor (slip r type).
Fan for cooling mounted on shaft.
• There are two types of induction motor depending upon the construction of
motor.
I. Squirrel Cage type
II.Wound rotor type.

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Working Principle of Three Phase Induction Motor -

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In an induction motor only the stator winding is fed with an AC supply.
 Alternating flux is produced around the stator winding due to AC supply. This
alternating flux revolves with synchronous speed. The revolving flux is called as
"Rotating Magnetic Field" (RMF).
 The relative speed between stator RMF and rotor conductors causes an induced emf
in the rotor conductors, according to the Faraday's law of electromagnetic
induction. The rotor conductors are short circuited, and hence rotor current is
produced due to induced emf. That is why such motors are called as induction
motors.

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(This action is same as that occurs in transformers, hence induction
motors can be called as rotating transformers.)
 Now, induced current in rotor will also produce alternating flux around
it. This rotor flux lags behind the stator flux.
 The direction of induced rotor current, according to Lenz's law, is such
that it will tend to oppose the cause of its production.

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 As the cause of production of rotor current is the relative velocity
between rotating stator flux and the rotor, the rotor will try to catch up
with the stator RMF.
 Thus the rotor rotates in the same direction as that of stator flux to
minimize the relative velocity.
 However, the rotor never succeeds in catching up the synchronous
speed. This is the basic working principle of induction motor.

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Applications of induction motor –
 Lifts
 Cranes
 Hoists
 Large capacity exhaust fans
 Driving lathe machines
 Crushers
 Oil extracting mills
 Textile and etc.

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Reversal of rotation of Induction Motor.
Q.10). State how you will reverse the direction of rotation of 3-phase induction motor.
Q.11). How the direction of 3 phase induction motor is reversed.
Q.12). State the method to reverse the direction of rotation of induction motor.
ANS –
Following factors that determine the direction of rotation of three phase induction motor
1. Phase sequence of supply
2. Direction of rotating magnetic field.
i.e. R-Y-B ---- clockwise direction
R-B-Y or Y-R-B --- anticlockwise direction

References
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Department Of Mechatronics, Sanjivani K. B. P.Polytechnic, Kopargaon S.C.Bhangale
 Electrical technology (Vol. II) - B. L. Theraja
 Electrical machines - Kothari D. P. & Nagrath I. J
 Fundamental of Electrical Engg. - Mittle & Mittal
 Special purpose electrical machines - S. K. Sen
 Sources from Internet

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THANK YOU…

Three phase induction motor – construction, operation & application..ppt

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Three phase induction motor – construction, operation & application..ppt