A Review of power quality problems, standards and solutions

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
Volume: 04 Issue: 01 | Jan -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1765
A Review of Power Quality Problems, Standards and Solutions
Pradeep Kumar
M.E Student, Department of Electrical Engineering,
National Institute of Technical Teachers’ Training and Research, Chandigarh-160019
pradeep02334@gmail.com
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Abstract - Power quality has become a major area of
concern in present era due to the increase in modern sensitive
and sophisticated loads connected to the Distribution System.
The electrical devices or equipments are pronetofailurewhen
exposed to one or more power quality problems. Theelectrical
device might be an electric motor, a transformer, a generator,
a computer, a printer, communication equipment, or a
household appliance reacts adversely to power quality issues
depending on the severity of problems.
This paper presents a review of the power quality problems,
issues, related international standards and the solution
techniques. Some power quality enhancement devicesarealso
listed. It is necessary for engineers, technicians, and system
operators to become familiar with power quality issues.
Key Words: Power quality issues, IEEE-519, Power
Conditioning Devices, Voltage spikes, Frequency variation,
voltage sag, Harmonics.
1.INTRODUCTION
Power Quality (PQ) related problems are of most concern
nowadays. The widespread application of electronic
equipments, like, information technology equipment,power
electronic based equipments suchasadjustablespeeddrives
(ASD), programmable logic controllers (PLC), energy-
efficient lighting, are completely changing the nature of
electric loads. The applications of such kind of electric loads
are the major victims of power quality problems. Due to
their non-linearity, such kind of electric loads cause
disturbances in the voltage waveform.
This paper discusses the major power quality problems,
related international standards and solutions based on an
extensive number of publications.
2. TYPES OF POWER QUALITY PROBLEMS
There are several aspects of power quality problems due to
which an electrical device may malfunction,fail prematurely
or not operate at all. Some of the most common power
supply problems and their likely effect on sensitive
equipment.
2.1 Voltage fluctuations
Voltage fluctuations are caused by arc furnaces, frequent
start/stop of electric motors (for instance elevators),
oscillating loads.Consequencesareundervoltages,flickering
of lighting and screens, giving the impression of
unsteadiness of visual perception.
2.2 Voltage dips and under voltage
Short duration under-voltages are called “Voltage Sags” or
“Voltage Dips [IEC]”. Voltage sag is a decreasetobetween 0.1
and 0.9 pu in rms voltage or current at the power frequency
for durations from 0.5 cycle to 1 min. The main causes of
voltage dips are fault in the system, starting of large loads.
Excessive network loading,lossofgeneration,incorrectly set
transformer taps and voltage regulator malfunctions,causes
under voltage which indirectly leadtooverloadingproblems
as equipment takes an increased current to maintain power
output (e.g. motor loads).
2.3 Voltage swell
Voltage swell is defined as an increase to between 1.1 and
1.8 pu in rms voltage or current at the power frequency for
durations from 0.5 cycle to 1 min. The major causes are
Start/stop of heavyloads,badlydimensionedpowersources,
badly regulated transformers(mainlyduringoffpeak hours).
Consequences are data loss, flickering of lighting and
screens, stoppage or damage of sensitive equipment, if the
voltage values are too high.
2.4 Very short interruption
Total interruption of electrical supply for duration from few
milliseconds to one or two seconds causes ripping of
protection devices, loss of information and malfunction of
data processing equipment. Mainly due to the opening and
automatic reclosure of protectiondevicesto decommissiona
faulty section of the network.
2.5 Long interruption
Long interruption of electrical supply for duration greater
than 1 to 2 seconds causes stoppage of all equipment. The
main fault causes are Equipment failureinthepower system
network, storms and objects (trees, cars, etc) striking lines

or poles, fire, human error, bad coordination or failure of
protection devices.
2.6 Harmonic distortion
Main Causes are electric machines working above the knee
of the magnetization curve (magnetic saturation), arc
furnaces, welding machines, rectifiers, and DC motor, all
non-linear loads, such as power electronics equipment
including adjustable speed drives (ASDs), switched mode
power supplies, data processing equipment, high efficiency
lighting. Consequences are increased probability in
occurrence of resonance, neutral overload in 3-phase
systems, overheating of all cables and equipment, loss of
efficiency in electric machines, electromagnetic interference
with communication systems, and errors in measures when
using average reading meters, nuisance tripping of thermal
protections.
2.7 Voltage unbalance
A voltage variation in a three-phase system in which the
three voltage magnitudes or the phase angle differences
between them are not equal. Causes are large single-phase
loads (induction furnaces, traction loads), incorrect
distribution of all single-phase loads by the three phases of
the system (this may be also due to a fault).Unbalancing
results in negative sequence that is harmful to all three
phase loads, particularly mostaffectedloadsarethree-phase
induction machines.
2.8 Voltage surges/spikes
Voltage rise that may be nearly instantaneous (spike) or
takes place over a longer duration (surge). A voltage surge
takes place when the voltage is 110%ormoreabovenormal.
The most common cause is heavy electrical equipmentbeing
turned off. Possible Solutions are surge suppressors,voltage
regulators, uninterruptable power supplies, power
conditioners.
2.9 High Voltage spikes
High-voltage spikes occur when there is a sudden voltage
peak of up to 6,000 volts. These spikes are usually the result
of nearby lightning strikes, but there can be other causes as
well. The effects on vulnerable electronic systems can
include loss of data and burned circuit boards. Possible
Solutions are using Surge Suppressors, Voltage Regulators,
Uninterruptable Power Supplies, Power Conditioners.
2.10 Frequency variation
A frequency variation involves a change in frequency from
the normally stable utility frequency of 50 or 60 Hz,
depending on geographic location. This may be caused by
erratic operation of emergency generators or unstable
frequency power sources. For sensitive equipment, the
results can be data loss, program failure, equipment lock-up
or complete shutdown. Possible Solutions are using Voltage
Regulators and Power Conditioners.
2.11 Brownouts
A brownout is a steady lower voltage state causes glitches,
data loss and equipment failure. An exampleofa brownoutis
what happens during peak electrical demandin thesummer,
when utilities can’t always meet the requirements and must
lower the voltage to limit maximum power. Possible
Solutions are using Voltage Regulators, Uninterruptable
Power Supplies, and Power Conditioners.
2.12 Blackouts
A power failure or blackout is a zero-voltage condition that
lasts for more than two cycles. It may be causedbytripping a
circuit breaker, power distribution failure or utility power
failure. A blackout can cause data loss or corruption and
equipment damage.
2.13 Noise
Superimposing of high frequency signalsonthewaveform of
the power-system frequency caused by microwaves,
television diffusion, and radiation due to welding machines,
arc furnaces, and electronic equipment,impropergrounding
etc. Consequences are disturbances on sensitive electronic
equipment, usually not destructive, data loss and data
processing errors.
2.14 Electrical line noise
Electrical line noise is defined as Radio Frequency
Interference (RFI) and Electromagnetic Interference (EMI)
and causes equipment to lock-up, and data error or loss.
Sources of the problems include motors, relays, motor
control devices, broadcast transmissions, microwave
radiation, and distant electrical storms. Possible Solutions
are using Voltage Regulators, Uninterruptable Power
Supplies, and Power Conditioner.
3. POWER QUALITY STANDARDS
PQ problems are the worldwide issue. To minimize the PQ
level some measures have been developed by International
organizations for the utility to deliver the quality electric
power to the end users. Standardization organizations like
IEC, CENELEC, and IEEE have developed set standards for
quality of electric power. In Europe, the most relevant
standards in PQ are the EN 50160 (by CENELEC) and IEC
61000. The power quality standards developed by IEEE do
not have such a structured and comprehensive set as

compared to European power quality standard IEC. Main
IEEE power quality standards are described in the ensuing
sections.
3.1 IEEE 519
IEEE standard 519-1992 is titledasRecommendedPractices
and Requirements for Harmonic Control in Electric Power
systems. The 1992 standard is a revision of an earlier IEEE
work published in 1981 covering harmonic control. The
basic themes of IEEE Standard 519 are twofold.
i. Electric utilities have theresponsibilitytoproducea
high quality supply in terms of voltage level and
waveform.
ii. Utility consumers must limit the harmonic currents
drawn from the line.
The responsibility of an electric utility is to deliver quality
electric power to the end user consumers. The quality
electrical power protects the electrical equipments from
overheating, loss of life from excessive harmonic currents,
and excessive voltage stress due to excessive harmonic
voltage.
IEEE 519 lists the harmonic distortion limits at the point of
common coupling. (PCC). The voltage distortion limits of 3
percent harmonic distortion for an individual frequency
component and 5 percent for total harmonic distortion.
In IEEE standard 519, all of harmonic limits are basedonthe
customer load mix and the location of sensitive &
sophisticated equipments in the power system. Such PQ
standards are not applied to particular equipment.
3.1.1 IEEE 519 Standard for Current Harmonics
i) General distribution systems [120 V-69 KV]:
Current distortion limits are for odd harmonics. Even
harmonics are limited to 25% of the odd Harmonic limits [1,
3, 5]. For all power generation equipment, distortion limits
are those with ISC/IL < 20. ISC is the maximum short circuit
current at the Point of Common Coupling “PCC”. IL is the
maximum fundamental frequency 15-or 30- minutes load
current at point of Common Coupling “PCC. TDD is the total
demand distortion (= THD normalized by IL are shown in
Table 2).
ii) General sub-transmission systems [69 Kv-161
kV]: The current harmonic distortion limits apply to limits
of harmonics that loads should draw from the utility at the
Point of Common Coupling “PCC”. Note that the harmonic
limits differ based on the ISC/IL rating, where ISC is the
maximum short circuit current at the PCC. I is the maximum
demand load current at the PCC.
ISC is short circuit current presents at the PCC. The
magnitude of ISC current is determined by the size,
impedance, and utility voltage connected to the Point of
Common Coupling “PCC”. IL is the maximum demand load
current, and it is measured at the PCC. The maximum
harmonic current distortion level is shown in Table 3.
Table 2. Current Distortion Limits For Harmonics
Table 3. Maximum Harmonic Current Distortion Level
3.1.1 IEEE Standard For Voltage Harmonics
According to IEEE standard 519, for power system voltage
limits below 69Kv, the harmonic distortion for an individual
frequency is limited to 3% and 5% for Total Harmonic
Distortion. The IEEE standard for voltage harmonics is
shown in Table 4.
Table 4. Voltage Distortion Limits For Harmonics
3.2. IEC 61000-3-2 and IEC 61000-3-4
3.2.1. IEC 61000-3-2 (1995-03)
This standard specified the limits for harmonic current
emissions from the electrical and electronic equipments
which having an input current up to and including 16 A per
phase, and intended to be connected to public low-voltage
distribution systems.Thetestsaccordingtothisstandard are
type tests [2,3,19].
3.2.2. IEC/TS 61000-3-4 (1998-10)
This standard specified for electrical and electronic
equipments having a rated input current more than16Aper

phase and intended to be connected in public low-voltage ac
distribution systems. The a.c distribution systems are of
following types:
i. Single-phase, two or three wires distribution
systems with a nominal voltage up to 240 V.
ii. Three-phase, three or four wires distribution
systems and nominal voltage up to 600 V.
iii. Nominal frequency 50 Hz or 60 Hz.
On the basis of these recommendations, theserviceprovider
can asses equipment regarding harmonic disturbanceandto
decide whether the equipment is acceptable for connection
in the electric power systems. European standards, IEC
61000-3-2 & 61000-3-4, placing current harmonic limits on
equipments. These equipments are designed in order to
protect the small consumer's equipment. The former is
restricted to 16 A and latter extends the range above 16 A.
3.3. IEEE Standard 141-1993, Recommended
Practice for Electric Power Distribution for
Industrial Plants
A thorough analysisofbasic electrical-systemconsiderations
is presented. Guidance is provided in design, construction,
and continuity of an overall system to achieve safety of life
and preservation of property; reliability; simplicity of
operation; voltage regulation in the utilization of equipment
within the tolerance limits under all load conditions; care
and maintenance; and flexibility to permit developmentand
expansion.
Practice for Grounding of Industrial and
Commercial Power Systems
This standard presents a thorough investigation of the
problems of grounding and the methods for solving these
problems. There is a separate chapter for grounding
sensitive equipment.
Practice fo1r Emergency and Standby Power
Systems for Industrial and Commercial
Applications
This standard is recommended engineeringpracticesforthe
selection and application of emergency and standby power
systems. It provides facility designers,operatorsandowners
with guidelines for assuring uninterrupted power, virtually
free of frequency excursions and voltage dips, surges, and
transients.
Practice for Design of Reliable Industrial and
Commercial Power Systems
The fundamentals of reliability analysis as it applies to the
planning and design of industrial and commercial electric
power distribution systems are presented. Included are
basic concepts of reliability analysis by probabilitymethods,
fundamentals of power system reliability evaluation,
economic evaluation of reliability,costofpoweroutagedata,
equipment reliability data, and examples of reliability
analysis. Emergency and standby power, electrical
preventive maintenance, and evaluating and improving
reliability of the existing plant are also addressed.
Practice for Powering and Grounding Sensitive
Electronic Equipment
Recommended design, installation, and maintenance
practices for electrical power and grounding(includingboth
power-related and signal-related noise control) of sensitive
electronic processing equipment used in commercial and
industrial applications.
3.8. IEEE Standard 1346-1998 Recommended
Practice for Evaluating Electric Power System
Compatibility with Electronic Process Equipment
A standard methodology for the technical and financial
analysis of voltage sag compatibility between process
equipment and electric powersystemsisrecommended. The
methodology presented is intended to be used as a planning
tool to quantify the voltage sag environment and process
sensitivity.
Practice for Monitoring Electric Power Quality
As its title suggests, this standard covers recommended
methods of measuring power-quality events. Manydifferent
types of power-quality measurement devices exist and it is
important for workers in different areas of power
distribution, transmission, and processing to use the same
language and measurement techniques. Monitoring of
electric power quality of AC power systems, definitions of
power quality terminology, impact of poor power qualityon
utility and customer equipment, and the measurement of
electromagnetic phenomena are covered.
3.10. IEEE Standard 1250-1995, Guide for Service
to Equipment Sensitive to Momentary Voltage
Disturbances
Computers, computer-like products, and equipment using
solidstate power conversionhavecreatedentirelynewareas
of power quality considerations. There is an increasing

awareness that much of this new user equipment is not
designed to withstand the surges, faults, and reclosing duty
present on typical distributionssystems.Momentaryvoltage
disturbances occurring in ac power distribution and
utilization systems, their potential effects on this new,
sensitive, user equipment, and guidance toward mitigation
of these effects are described. Harmonic distortionlimitsare
also discussed.
3.11. IEEE Standards Related to Voltage Sag and
Reliability
The distribution voltage quality standard i.e. IEEE Standard
P1564 gives the recommended indices and procedures for
characterizing voltage sag performance and comparing
performance across different systems. A new IEC Standard
61000-2-8 titled “Environment Voltage Dips and Short
Interruptions” has come recently. This standard warrants
considerable discussion within the IEEE to avoid conflicting
methods of characterizing system performance in different
parts of the world.
3.12. IEEE Standards Related to Flicker
Developments in voltage flicker standardsdemonstratehow
the industry can successfully coordinate IEEE and IEC
activities. IEC Standard 61000-4-15 defines the
measurement procedure and monitor requirements for
characterizing flicker. The IEEE flickertask forceworking on
Standard P1453 is set to adopt the IEC standard as its own.
3.13. Standards related to Custom Power
IEEE Standard P1409 is currently developing an application
guide for custom power technologies to provide enhanced
power quality on the distribution system. This is an
important area for many utilities that may want to offer
enhanced power quality services.
3.14. Standards related to Distributed Generation
The new IEEE Standard P1547 provides guidelines for
interconnecting distributed generation with the power
system.
3.15. 420-2013 - IEEE Standard for the Design and
QualificationofClass1EControlBoards,Panelsand
Racks Used in Nuclear Power Generating Stations
This standard specifies the design requirements for new
and/or modified Class 1E control boards, panels, and racks
and establishes the methods to verify that these
requirements have been satisfied. Methods for meeting the
separation criteria contained in IEEE Std 384 are addressed.
Qualification is also included to address the overall
requirements of IEEE Std 323 and recommendationsofIEEE
Std 344.
3.16. IEEE Standard 384-2008 - IEEE Standard
Criteria for Independence of Class 1E Equipment
and Circuits
The independence requirements of the circuits and
equipment comprising or associated with Class 1E systems
are described. Criteria for the independence that can be
achieved by physical separation and electrical isolation of
circuits and equipment that are redundant are set forth. The
determination of what is to be considered redundant is not
addressed.
3.17.IEEE Standard C57.18.10-1998 – IEEE
Standard Practices and Requirements for
Semiconductor Power Rectifier Transformers
Practices and requirements for semiconductor power
rectifier transformers for dedicated loads ratedsinglephase
300 kW and above and three-phase 500 kW and above are
included. Static precipitators, high-voltageconvertersforDC
power transmission, and othernonlinearloadsare excluded.
Service conditions, both usual and unusual, are specified, or
other standards are referenced as appropriate.Routinetests
are specified. An informative annex provides several
examples of load loss calculations for transformers when
subjected to non-sinusoidal currents, based on calculations
provided in the standard.
3.18. IEEE Standard C57.21-1990 -IEEE Standard
Requirements, Terminology and Test Code for
Shunt Reactors Rated Over 500 kVA
All oil-immersed or dry-type, single-phase or three-phase,
outdoor or indoor shunt reactors rated over 500 kVA are
covered. Terminology and general requirements are stated,
and the basis for rating shunt reactors is set forth. Routine,
design, and other tests are described, and methods for
performing them are given. Losses and impedance,
temperature rise, dielectric tests, and insulation levels are
covered. Construction requirements for oil-immersed
reactors and construction and installation requirements for
dry-type reactors are presented.
4. POWER QUALITY SOLUTIONS
4.1. Power Conditioning Devices
The following devices play a crucial role in improving power
quality strategy.
4.1.1 Transient Voltage Surge Suppressor (TVSS)
It provides the simplest andleastexpensivewaytocondition
power. These units clamp transient impulses (spikes) to a
level that is safe for the electronic load. Transient voltage
surge suppressors are used as interface between the power
source and sensitive loads, so that the transient voltage is

clamped by the TVSS before it reaches the load.TVSS usually
contain a component with a nonlinear resistance (a metal
oxide varistor or a zener diode) that limits excessive line
voltage and conduct any excess impulse energy to ground.
4.1.2 Filters
Filters are categorized into noise filters, harmonic filters
(active and passive) etc. Noise filters are used to avoid
unwanted frequency current or voltage signals (noise) from
reaching sensitive equipment. This can be accomplished by
using a combination of capacitors and inductances that
creates a low impedance path to the fundamental frequency
and high impedance to higher frequencies,thatis,a low-pass
filter. Harmonic filters are used to reduce undesirable
harmonics. Passive filters consist in a lowimpedancepathto
the frequencies of the harmonics to be attenuated using
passive components (inductors, capacitors and resistors).
4.1.3 Isolation Transformers
Isolation transformers are used to isolate sensitive loads
from transients and noise deriving from the mains. The
particularity of isolation transformers is a grounded shield
made of nonmagnetic foil located between the primary and
the secondary. Any noise or transient that come from the
source in transmitted through the capacitance between the
primary and the shield and on to the ground and does not
reach the load. Isolation transformers reduce normal and
common mode noises, however, they do not compensate for
voltage fluctuations and power outages.
Fig-1: Noise attenuation by Isolation Transformer.
4.1.4 Voltage Regulator
Voltage regulators are normally installed where the input
voltage fluctuates, but total loss of power is uncommon.
There are three basic types of regulators:
i. Tap Changers- Designed to adjustforvaryinginput
voltages by automaticallytransferringtapsona
power transformer.
ii. Buck Boost- Utilize similar technology to the tap
changers except the transformerisnotisolated.
iii. Constant Voltage Transformer (CVT)-Also
known as ferroresonant transformers.TheCVT
is a completely static regulator thatmaintainsa
nearly constant output voltage during large
variations in input voltage.
4.1.5Uninterrupted Power Supply (UPS)
UPS systems provide protection in the case of a complete
power interruption (blackout). They should be applied
where “down time” resulting from any loss of power is
unacceptable. UPS are designed to provide continuous
power to the load in the event of momentary interruptions.
They also provide varying degreesofprotectionfromsurges,
sags, noise or brownouts depending on the technologyused.
There are three major UPS topologies each providing
different levels of protection:
a) Off-Line UPS (also called Standby)
Low cost solution for small, less critical, stand-alone
applications such as programmable logic controllers,
personal computers and peripherals. Advantages of off-line
UPS are high efficiency, low cost and high reliability.
b) Line-Interactive UPS
Line-Interactive UPS provides
highly effective power conditioning plus battery backup.
Advantages are good voltage regulation and high efficiency.
Disadvantages are noticeable transfer time and difficulty in
comparing competing units.
c) True On-Line UPS
True On-Line UPS provides the highest level of power
protection, conditioning and power availability. Advantages
of the online UPS include the eliminationofanytransfertime
and superior protection from voltage fluctuations.

Fig- 2: Offline UPS System
Fig-3: Online UPS system
4.1.6 Dynamic Static Compensator D-STATCOM
The D-STATCOM is one of the most effective Custom power
devices used in a distribution network. It is a three-phase
and shunt connected power electronics based device which
is connected near the load at the distribution systems. The
schematic diagram of a D-STATCOM (Distribution Static
Compensator), is shown in Figure-6.Itconsistsofa two-level
Voltage Source Converter (VSC), a dc energy storage device,
a coupling transformer connected in shunt to the
distribution network through a coupling transformer. The
VSC converts the dc voltage across the storage device into a
set of three-phase ac output voltages. These voltages are in
phase and coupled with the ac system through thereactance
of the coupling transformer. Suitable adjustment of the
phase and magnitude of the D-STATCOM output voltages
allows effective control of active and reactive power
exchanges between the DSTATCOM and the ac system. Such
configuration allows the device to absorb or generate
controllable active and reactive power.
The voltage-source converter (VSC) connectedinshunt with
the ac system provides a multifunctional topologywhichcan
be used for up to three quite distinct purposes:
1. Voltage regulation and compensation of reactive power
2. Correction of power factor.
3. Elimination of current harmonics.
A voltage-source converter (VSC) is a power electronic
device as shown in Fig 4. The function of a VSC is to generate
a sinusoidal voltage with minimal harmonic distortion from
a DC voltage and connected to AC distribution line through
coupling transformer. The DC side of the voltage-source
converter (VSC) is connected to a DC capacitor.
Fig.4. The Schematic diagram of a DSTATCOM
(Distribution Static Compensator)
The AC terminals of the converter are connectedtothePoint
of Common Coupling (PCC) through an inductance asshown
in Fig. 4, such inductance could be a filter inductance or the
leakage inductance of the coupling transformer. A dc
capacitor could be charged by a battery source, or could be
precharged by the converter itself. The output voltage of the
voltage-source converter VSC is compared with AC bus
voltage. If the voltage of a converter is equal to the AC
terminal voltage, the reactive power exchange is zero. When
the AC terminal voltage magnitude is greater than that of
voltage-source converter (VSC) voltage, theDSTATCOMisin
the capacitive mode of operation and viceversa.Theamount
of reactive power flow is proportional tothedifferencein the
two voltages.
If the D-STATCOM has a DC source or energy storage device
on its DC side, it can supply real power to the distribution
networks. The active power flow is controlled by the angle

between the ac terminal and voltage-sourceconverter(VSC)
voltages. When phase angle of the AC terminal voltage leads
the voltage-source converter (VSC) phase angle, the D-
STATCOM absorbs the real power from the distribution
networks. If the phase angle of the AC terminal voltage lags
the voltage-source converter (VSC) phase angle, the D-
STATCOM supplies real power to distributionnetworks. The
DSTATCOM operates in both current and voltage control
modes.
4.1.7 Unified Power Quality conditioner (UPQC)
The Unified Power Quality Conditioner (UPQC) is a custom
power device that consists of two voltage source inverters
(VSI) is connected to a dc energy storage capacitor.
Fig.5. Schematic diagram of a Unified Power Quality
conditioner (UPQC).
The schematic diagram of a Unified Power Quality
conditioner is shown in Fig.9. A UPQC, combines the
operations of a Distribution Static Compensator
(DSTATCOM) and Dynamic Voltage Regulator (DVR)
together. This combination allows a simultaneous
compensation of the load currents and the supply voltages,
so that compensated current drawn from the network and
the compensated supply voltage delivered to the load are
sinusoidal and balanced. It places in the distribution system
to reduce the disturbances that impact on the performance
load. UPQC is the only multi functioning device which can
reduce several problems power quality problems.
4.1.8 Thyristor based Static switch
The static switch is a versatile device for switching a new
element into the circuit when voltage support is needed. To
correct quickly for voltage spikes, sags, or interruptions, the
static switch can be used to switch in capacitor, filter,
alternate power line, energy storage system etc. It protects
against 85% of the interruptions and voltage sags.
4.1.9 Motor Generator (MG) Set
They are usually used as a backup power source for a
facility’s critical systems such as elevators and emergency
lighting in case of blackout. However, they do not offer
protection against utility power problems such as over
voltages and frequency fluctuations. Motor generators are
consists of an electric motor driving a generator with
coupling through a mechanical shaft. This solution provides
complete decoupling from incoming disturbances such as
voltage transients, surges and sags.
4.1.10 Static VAR compensator (SVC)
Static VAR compensators (SVC) use a combination of
capacitors and reactors to regulate the voltage quickly.
Solidstate switches control the insertion of the capacitors
and reactors at the right magnitude to prevent the voltage
from fluctuating.
Fig-6 Static VAR compensator using TCR and TSC.
It is normally applied to transmission networks to counter
voltage dips/surges during faults and enhance power
transmission capacity on long.
4.2 Energy Storage System
4.2.1 Flywheels
A flywheel is an electromechanical device that couples a
rotating electric machine (motor/generator) with a rotating
mass to store energy for short durations. The
motor/generator draws power provided by the grid to keep
the rotor of the flywheel spinning. During a power
disturbance, the kinetic energy stored in the rotor is
transformed to DC electric energy by the generator, and the
energy is delivered at a constant frequency and voltage
through an inverter and a control system. Advanced
flywheels constructed from carbon fiber materials and
magnetic bearings can spininvacuumatspeedsupto40,000

to 60,000 RPM. The stored energy is proportional to the
moment of inertia and to the square of the rotational speed.
High speed flywheels can store much more energy than the
conventional flywheels. Flywheels typically provide 1-100
seconds of ride-through time, and back-up generators are
able to get online within 5-20 seconds.
4.2.2 Super capacitors
Super capacitors (also known as ultra capacitors) are DC
energy sources and must be interfaced to the electric grid
with a static power conditioner, providing energy output at
the grid frequency. A super capacitor providespowerduring
short duration interruptions or voltage sags. Medium size
super capacitors (1 M Joule) are commercially available to
implement ride-through capability in small electronic
equipment, but large super capacitors are still in
development, but may soon become a viable component of
the energy storage field. Capacitance is very large because
the distance between the plates is very small (several
angstroms), and because the area of conductor surface (for
instance of the activated carbon) reaches 1500-2000 m2/g
(16000-21500 ft2/g). Thus, the energy stored by such
capacitors may reach 50-60 J/g.
4.2.3 Super Conducting Magnetic Energy Storage
(SMES)
A magnetic field is created by circulating a DC current in a
closed coil of superconducting wire. The path of the coil
circulating current can be opened with a solid-state switch,
which is modulated on and off. Due to the high inductance of
the coil, when the switch is off (open), the magnetic coil
behaves as a current source and will force current into the
power converter which will charge to some voltage level.
Proper modulation of the solid-state switch can hold the
voltage within the proper operating range of the inverter,
which converts the DC voltage into AC power. Low
temperature SMES cooled by liquid helium is commercially
available. High temperature SMES cooled by liquid nitrogen
is still in the development stage and may become a viable
commercial energy storage source in the future due to its
potentially lower costs. SMES systems are large and
generally used for short durations, such as utility switching
events.
5. IMPROVE POWER QUALITY
5.1. Grounding & Bonding Integrity
Computer based industrial system performance is directly
related to the quality of the equipment grounding and
bonding. If the grounding and bonding is incorrectly
configured, poor system performance is the result.
Grounding is one of the most important and misunderstood
aspects of the electrical system. It is essential todifferentiate
the functions of the grounded conductor (neutral) from the
equipment grounding system (safety ground). The safety
ground protects the electrical system and equipment from
super-imposed voltages caused by lightning or accidental
contact with higher voltage systems. It also prevents static
charges build-up. The safety ground establishes a “zero-
voltage” reference point for the system. The safety ground
must be a low impedance path from the equipment to the
bonding point to the grounding electrode at the service
entrance. This allows fault currents high enough to clear the
circuit interrupters in the system preventing unsafe
conditions.
The grounded conductor (neutral) is a current carrying
conductor which is bonded to the grounding system at one
point.
Grounding this conductor limits the voltage potential inside
the equipment in reference to grounded parts. Neutral and
ground should only be bonded together at the service
entrance or after a separately derived source. One of the
most common errors in a system is bonding the neutral to
ground in multiple locations. Whether intentional or
unintentional, these ‘extra’ bonding points should be
identified and eliminated. Proper grounding and bonding
minimizes costly disturbances.
5.2. Proper Wiring
An overall equipment inspection is crucial to ensure proper
wiring within a facility. The entire electrical system should
be checked for loose, missing or improper connections at
panels, receptacles and equipment. Article 300 of the
National Electrical Codecoverwiringmethodsandshouldbe
followed to ensure safe and reliable operation. There are
many types of commonly available circuit testersthatcan be
used to check for improper conditions such as reversed
polarity, open neutral or floating grounds. Make certain to
isolate panels feeding sensitive electronic loads from heavy
inductive loads, or otherelectricallynoisyequipmentsuchas
air compressors or refrigeration equipment. Also check
neutral and ground conductors to make sure they are not
shared between branch circuits.
5.3. Power Disturbances
Voltage fluctuations and noise are common power
disturbances present in any electrical environment that
directly affect electronic equipment. These disturbances
exist in numerous forms including transients, sags, swells,
over voltages, under voltages,harmonics,outages,frequency
variations andhighfrequencynoise.Harmonicdistortion has
emerged as significant problem due to the increased use of
electronic equipment. This electronic equipment draws
current that is not linear to the voltage waveform. This non-
linear current can cause high neutral current, overheated
neutral conductors, overheated transformers, voltage
distortion and breaker tripping. Loads such as solid-state
controls for adjustable speed motors, computers and

switched mode power supplies are sources of non-linear
currents. The Information Technology Industry Council
(ITIC) has revised the CBEMA curve in 2000. This curve is
used to define the voltage operating envelope within which
electronic equipment should operate reliably. Equipment
should be able to tolerate voltage disturbances in the “no
interruption” region of the chart. When the voltage
disturbance is in the “no-damage” region, the equipment
may not operate properly, but should recover when voltage
returns to normal. If voltages reach the “prohibited region,”
connected equipment may be permanently damaged.
Expensive equipment should be protected from voltages in
the prohibited region. Processes which require high
reliability should be protected from both the prohibited and
no-damage regions.
6. Conclusion
The availability of electric power with high quality is crucial
for the running of the modern society. If some sectors are
satisfied with the quality of the power provided by utilities,
some others are more demanding. To avoid the huge losses
related to PQ problems, the most demanding consumers
must take action to prevent the problems. Among the
various measures, selection of less sensitive equipment can
play an important role. This paper presented a review of the
power quality problems, issues, and related international
standards. This paper will help research workers, users and
suppliers of electrical power to gain a guideline about the
power quality.
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AUTHOR
Pradeep Kumar received the B.Tech
degree in Electrical Engineering from
Uttar Pradesh Technical University,
Lucknow. He is Master of Engineering
(Instrumentation and Control) Final
year student, Department of Electrical
Engineering, National Institute of
Technical Teachers’ Training and
Research, Chandigarh, India. His
research interests include, power
quality, special machines, Power
Electronics.
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