Power Quality in Power Systems and Electrical Machines, Second Edition ( TQL.com )

POWER QUALITY
IN POWER SYSTEMS
AND ELECTRICAL
MACHINES


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POWER QUALITY
IN POWER SYSTEMS
AND ELECTRICAL
MACHINES
Second Edition
MOHAMMAD A.S. MASOUM
EWALD F. FUCHS

AMSTERDAM • BOSTON • HEIDELBERG • LONDON
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CONTENTS

Preface
Acknowledgments

1. Introduction to Power Quality
1.1 Definition of power quality

1.2 Causes of disturbances in power systems
1.3 Classification of power quality issues
1.4 Formulations and measures used for power quality
1.5 Effects of poor power quality on power system devices
1.6 Standards and guidelines referring to power quality
1.7 Harmonic modeling philosophies
1.8 Power quality improvement techniques
1.9 Summary
1.10 Problems
References
Additional bibliography

2. Harmonic Models of Transformers
2.1 Sinusoidal (linear) modeling of transformers
2.2 Harmonic losses in transformers
2.3 Derating of single-phase transformers
2.4 Nonlinear harmonic models of transformers
2.5 Ferroresonance of power transformers
2.6 Effects of solar-geomagnetic disturbances on power systems and transformers
2.7 Grounding
2.8 Measurement of derating of three-phase transformers
2.9 Summary
2.10 Problems
References
Additional bibliography

3. Modeling and Analysis of Induction Machines
3.1
3.2

Complete sinusoidal equivalent circuit of a three-phase induction machine
Magnetic fields of three-phase machines for the calculation of inductive
machine parameters

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3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11

Steady-state stability of a three-phase induction machine
Spatial (space) harmonics of a three-phase induction machine
Time harmonics of a three-phase induction machine
Fundamental and harmonic torques of an induction machine

Measurement results for three- and single-phase induction machines
Inter- and subharmonic torques of three-phase induction machines
Interaction of space and time harmonics of three-phase induction machines
Conclusions concerning induction machine harmonics
Voltage-stress winding failures of ac motors fed by variable-frequency,
voltage- and current-source pwm inverters
3.12 Nonlinear harmonic models of three-phase induction machines
3.13 Static and dynamic rotor eccentricity of three-phase induction machines
3.14 Operation of three-phase machines within a single-phase power system
3.15 Classification of three-phase induction machines
3.16 Summary
3.17 Problems
References
Additional bibliography

4. Modeling and Analysis of Synchronous Machines
Sinusoidal state-space modeling of a synchronous machine in the time
domain
4.2 Steady-state, transient, and subtransient operation
4.3 Harmonic modeling of a synchronous machine
4.4 Summary
4.5 Problems
References
Additional bibliography

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5. Interaction of Harmonics with Capacitors
5.1 Application of capacitors to power-factor correction
5.2 Application of capacitors to reactive power compensation
5.3 Application of capacitors to harmonic filtering
5.4 Power quality problems associated with capacitors
5.5 Frequency and capacitance scanning
5.6 Harmonic constraints for capacitors
5.7 Equivalent circuits of capacitors
5.8 Summary
5.9 Problems
References

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Contents

6. Lifetime Reduction of Transformers and Induction Machines
6.1
6.2
6.3
6.4
6.5
6.6
6.7

6.8
6.9

Rationale for relying on the worst-case conditions
Elevated temperature rise due to voltage harmonics
Weighted-harmonic factors
Exponents of weighted-harmonic factors
Additional losses or temperature rises versus weighted-harmonic factors
Arrhenius plots
Reaction rate equation
Decrease of lifetime due to an additional temperature rise
Reduction of lifetime of components with activation energy E ¼ 1.1 eV due to
harmonics of the terminal voltage within residential or commercial utility systems
6.10 Possible limits for harmonic voltages
6.11 Probabilistic and time-varying nature of harmonics
6.12 The cost of harmonics
6.13 Temperature as a function of time
6.14 Various operating modes of rotating machines
6.15 Summary
6.16 Problems
References

7. Power System Modeling under Nonsinusoidal Operating Conditions
7.1 Overview of a modern power system
7.2 Power system matrices
7.3 Fundamental power flow
7.4 Newton-based harmonic power flow
7.5 Classification of harmonic power flow techniques
7.6 Summary
7.7 Problems

References

8. Impact of Poor Power Quality on Reliability, Relaying and Security
8.1 Reliability indices
8.2 Degradation of reliability and security due to poor power quality
8.3 Tools for detecting poor power quality
8.4 Tools for improving reliability and security
8.5 Load shedding and load management
8.6 Energy-storage methods
8.7 Matching the operation of intermittent renewable power plants with energy storage
8.8 Summary
8.9 Problems
References
Additional bibliography

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Contents

9. The Roles of Filters in Power Systems and Unified Power
Quality Conditioners
9.1 Types of nonlinear loads
9.2 Classification of filters employed in power systems
9.3 Passive filters as used in power systems
9.4 Active filters
9.5 Hybrid power filters
9.6 Block diagram of active filters
9.7 Control of filters
9.8 Compensation devices at fundamental and harmonic frequencies
9.9 Unified power quality conditioner (UPQC)
9.10 The UPQC control system
9.11 UPQC control using the park (DQO) transformation
9.12 UPQC control based on the instantaneous real and imaginary power theory
9.13 Performance of the UPQC
9.14 Summary
References

10. Optimal Placement and Sizing of Shunt Capacitor Banks in the
Presence of Harmonics
10.1
10.2
10.3
10.4

Reactive power compensation

Common types of distribution shunt capacitor banks
Classification of capacitor allocation techniques for sinusoidal operating conditions
Optimal placement and sizing of shunt capacitor banks in the presence
of harmonics
10.5 Summary
References

11. Power Quality Solutions for Renewable Energy Systems
11.1
11.2
11.3
11.4
11.5
11.6
11.7
11.8
11.9
11.10
11.11

Energy conservation and efficiency
Photovoltaic and thermal solar (power) systems
Horizontal – and vertical-axes wind power (WP) plants
Complementary control of renewable plants with energy storage plants
AC transmission lines versus DC lines
Fast-charging stations for electric cars
Off-shore renewable plants
Metering
Other renewable energy plants
Production of automotive fuel from wind, water, and CO2

Water efficiency

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11.12 Village with 2,600 inhabitants achieves energy independence
11.13 Summary
11.14 Problems
References
Appendix
Appendix
Appendix
Appendix
Index

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PREFACE

The increased use of power electronic components within the distribution system and the
reliance on renewable energy sources which have converters as interface between the
source and the power system lead to power quality problems for the operation of
machines, transformers, capacitors and power systems. The subject of power quality is
very broad by nature. It covers all aspects of power system engineering from transmission
and distribution level analyses to end-user problems. Therefore, electric power quality
has become the concern of utilities, end users, architects and civil engineers as well as
manufacturers. The book is intended for undergraduate or graduate students in electrical
and other engineering disciplines as well as for professionals in related fields. It is assumed
that the reader has already completed electrical circuit analysis courses covering basic
concepts such as Ohm’s, Kirchhoff’s, Ampere’s and Faraday’s laws as well as Norton
and Thevenin equivalent circuits and Fourier analysis. In addition, knowledge of diodes
and transistors and an introductory course on energy conversion (covering energy
sources, transformers, simple control circuits, rudimentary power electronics, transformers, single- and three-phase systems as well as various rotating machine concepts

such as brushless DC machines, induction and synchronous machines) is desirable.
This book has evolved from the content of courses given by the authors at the
University of Colorado at Boulder, USA, the Iran University of Science and Technology
at Tehran, Iran, and the Curtin University at Perth, Australia. The book is suitable for
both electrical and non-electrical engineering undergraduate and postgraduate students.
It has been particularly written for students or practicing engineers who want to teach
themselves through the inclusion of 135 application examples with solutions and
115 problems at the end of each chapter dealing with practical applications. 924 references are given in this book: mostly journal and conference papers as well as national
and international standards and guidelines. The International System (SI) of units has
been used throughout with some reference to the American/English system of units.
Power quality of power systems affects all connected electrical and electronic equipment, and is a measure of deviations in voltage, current, frequency, temperature, force,
and torque of particular supply systems and their components. In recent years there has
been considerable increase in nonlinear loads, in particular distributed loads such as computers, TV monitors and lighting. These draw harmonic currents which have detrimental
effects including communication interference, loss of reliability, increased operating
costs, equipment overheating, electrical machine, transformer and capacitor failures,
and inaccurate power metering. This subject is pertinent to engineers involved with
power systems, electrical machines, electronic equipment, computers and manufacturing

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Preface

equipment. This book helps readers to understand the causes and effects of power quality
problems such as nonsinusoidal wave shapes, voltage outages, harmonic losses, origins of
single-time events such as voltage dips, voltage reductions, and outages, along with techniques to mitigate these problems. Analytical as well as measuring techniques are applied
to power quality problems as they occur in existing systems based on central power stations and distributed generation mainly relying on renewable energy sources.
It is important for each power engineering student and professional who is active in

the area of distribution systems and renewable energy that he/she knows solutions to
power quality problems of electrical machines and power systems: this requires detailed
knowledge of modeling, simulation and measuring techniques for transformers,
machines, capacitors and power systems, in particular fundamental and harmonic power
flow, relaying, reliability and redundancy, load shedding and emergency operation,
islanding of power system and its voltage and frequency control, passive and active filtering methods, and energy storage combined with renewable energy sources. An intimate knowledge of guidelines and standards as well as industry regulations and practices is
indispensable for solving power quality problems in a cost-effective manner. These
aspects are addressed in this book which can be used either as a teaching tool or as a
reference book.
In this second edition of the book, we have included Chapter 11 of the first addition
in Chapter 9 “The Roles of Filters in Power Systems and Unified Power Quality Conditioners” and added new Chapter 11 “Power Quality Solutions for Renewable Energy
Systems” relating power quality solutions to renewable energy systems and sources.

Key features:
• Provides theoretical and practical insight into power quality problems of machines and
systems.
• 135 practical application (example) problems with solutions.
• 115 problems at the end of each chapter dealing with practical applications.
• 924 references mostly journal and conference papers as well as national and international standards and guidelines.


ACKNOWLEDGMENTS

The authors wish to express their appreciation to their families, in particular to wives
Wendy Fuchs and Roshanak Masoum, sons Franz Fuchs, Amir and Ali Masoum, and
daughters Heidi Fuchs and Maryam Masoum for their help in shaping and proofreading
the manuscript. In particular, the encouragement and support for research at the University of Colorado by Dipl.-Ing. Dietrich J. Roesler, formerly with the US Department of
Energy, Washington DC, who was one of the first professionals coining the concept of
power quality more than 32 years ago, is greatly appreciated. Lastly, the work initiated by
the late Professor Edward A. Erdelyi of the University of Colorado, doctoral advisor to

Ewald F. Fuchs, is reflected in part of this book.
Mohammad A.S. Masoum, Professor
Curtin University
Department of Electrical and Computer Engineering
GPO Box U1987, Perth, WA 6845, Australia
or
Ewald F. Fuchs, Professor
University of Colorado
Department of Electrical, Computer, and Energy Engineering,
Campus Box 425, Boulder, CO 80309, USA
or
July 2015

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CHAPTER 1

Introduction to Power Quality
Contents
1.1 Definition of Power Quality
1.2 Causes of Disturbances in Power Systems
1.3 Classification of Power Quality Issues
1.3.1 Transients
1.3.2 Short-duration voltage variations
1.3.3 Long-duration voltage variations
1.3.4 Voltage imbalance

1.3.5 Waveform distortion
1.3.6 Voltage fluctuation and flicker
1.3.7 Power–frequency variations
1.4 Formulations and Measures Used for Power Quality
1.4.1 Harmonics
1.4.2 The average value of a nonsinusoidal waveform
1.4.3 The rms value of a nonsinusoidal waveform
1.4.4 Form factor (FF)
1.4.5 Ripple factor (RF)
1.4.6 Harmonic factor (HFh)
1.4.7 Lowest order harmonic (LOH)
1.4.8 Total harmonic distortion (THD)
1.4.9 Total interharmonic distortion (TIHD)
1.4.10 Total subharmonic distortion (TSHD)
1.4.11 Total demand distortion (TDD)
1.4.12 Telephone influence factor (TIF)
1.4.13 C-message weights
1.4.14 V · T and I · T products
1.4.15 Telephone form factor (TFF)
1.4.16 Distortion index (DIN)
1.4.17 Distortion power (D)
1.4.18 Application example 1.1: Calculation of input/output currents and voltages of a
three-phase thyristor rectifier
Solution to application example 1.1:
1.4.19 Application example 1.2: Calculation of input/output currents and voltages of a
three-phase rectifier with one self-commutated electronic switch
Solution to application example 1.2:

Power Quality in Power Systems and Electrical Machines
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Power Quality in Power Systems and Electrical Machines

1.5
1.6

1.7

1.8

1.4.20 Application example 1.3: Calculation of input currents of a brushless DC
motor in full-on mode (three-phase permanent-magnet motor fed by a
six-step inverter)
Solution to application example 1.3:
1.4.21 Application example 1.4: Calculation of the efficiency of a polymer electrolyte
membrane (PEM) fuel cell used as energy source for a variable-speed drive
Solution to application example 1.4:
1.4.22 Application example 1.5: Calculation of the currents of a wind-power plant PWM
inverter feeding power into the power system
Solution to application example 1.5:

Effects of Poor Power Quality on Power System Devices
Standards and Guidelines Referring to Power Quality
1.6.1 IEC 61000 series of standards for power quality
1.6.2 IEEE-519 standard
Harmonic Modeling Philosophies
1.7.1 Time-domain simulation
1.7.2 Harmonic-domain simulation
1.7.3 Iterative simulation techniques
1.7.4 Modeling harmonic sources
Power Quality Improvement Techniques
1.8.1 High power quality equipment design
1.8.2 Harmonic cancellation
1.8.3 Dedicated line or transformer
1.8.3.1 Application example 1.6: Interharmonic reduction by dedicated transformer

Solution to application example 1.6:
1.8.4 Optimal placement and sizing of capacitor banks
1.8.5 Derating of power system devices
1.8.6 Harmonic filters, APLCs, and UPQCs

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1.8.6.1 Application example 1.7: Hand calculation of harmonics produced
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1.8.6.2 Application example 1.8: Filter design to meet IEEE-519 requirements

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Solution to application example 1.8:

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1.8.6.3 Application example 1.9: Several users on a single distribution feeder

Solution to application example 1.9:
1.9 Summary
1.10 Problems
Problem 1.1: Delta/wye three-phase transformer configuration
Problem 1.2: Voltage phasor diagrams of a three-phase transformer in delta/zigzag
connection
Problem 1.3: Current phasor diagrams of a three-phase transformer in delta/zigzag
connection with line-to-line load
Problem 1.4: Current phasor diagrams of a three-phase transformer in delta/zigzag
connection with line-to-neutral load
Problem 1.5: Current phasor diagrams of a three-phase transformer in delta/zigzag
connection with three-phase unbalanced load

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Introduction to Power Quality

Problem 1.6: Delta/zigzag three-phase transformer configuration without filter
Problem 1.7: Delta/zigzag three-phase transformer configuration with filter
Problem 1.8: Transient performance of a brushless DC motor fed by a fuel cell
Problem 1.9: Transient performance of an inverter feeding into three-phase power
system when supplied by a fuel cell
Problem 1.10: Suppression of subharmonic of 30 Hz with a dedicated transformer
Problem 1.11: Harmonic currents of a feeder
Problem 1.12: Design a filter so that the displacement (fundamental power) factor
cos ftotal
cos ftotal
1.0
1withfilter will be 0.9 lagging (consumer notation)
1withfilter
Problem 1.13: Passive filter calculations as applied to a distribution feeder with
one user including a twelve-pulse static power converter load
Problem 1.14: Passive filter calculations as applied to a distribution feeder with
two users each with a six-pulse static power converter load
Problem 1.15: Design two series LC filters so that the total displacement power
factor cos ftotal
cos ftotal
1.0, and the
1withfilter will be 0.9 lagging
1withfilter
recommendations according to IEEE-519 are satisfied
References
Additional Bibliography

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The subject of power quality is very broad by nature. It covers all aspects of power system
engineering, from transmission and distribution level analyses to end-user problems.
Therefore, electric power quality has become the concern of utilities, end users, architects, and civil engineers as well as manufacturers. These professionals must work
together in developing solutions to power quality problems:
• Electric utility managers and designers must build and operate systems that take into
account the interaction between customer facilities and power system. Electric utilities must understand the sensitivity of the end-use equipment to the quality of
voltage.
• Customers must learn to respect the rights of their neighbors and control the quality of
their nonlinear loads. Studies show that the best and the most efficient solution to
power quality problems is to control them at their source. Customers can perform this
by careful selection and control of their nonlinear loads and by taking appropriate
actions to control and mitigate single-time disturbances and harmonics before connecting their loads to the power system.
• Architects and civil engineers must design buildings to minimize the susceptibility and
vulnerability of electrical components to power quality problems.
• Manufacturers and equipment engineers must design devices that are compatible with
the power system. This might mean a lower level of harmonic generation or less sensitivity to voltage distortions.
• Engineers must be able to devise ride-through capabilities of distributed generators

(e.g., wind and solar generating plants).

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Power Quality in Power Systems and Electrical Machines

This chapter introduces the subject of electric power quality. After a brief definition of power quality and its causes, detailed classification of the subject is presented. The formulations and measures used for power quality are explained and
the impacts of poor power quality on power system and end-use devices such as
appliances are mentioned. A section is presented addressing the most important
IEEE [1] and IEC [2] standards referring to power quality. The remainder of
this chapter introduces issues that will be covered in the following chapters, including modeling and mitigation techniques for power quality phenomena in electric
machines and power systems. This chapter contains nine application examples and ends
with a summary.

1.1 DEFINITION OF POWER QUALITY
Electric power quality has become an important part of power systems and electric
machines. The subject has attracted the attention of many universities and industries,
and a number of books have been published in this exciting and relatively new
field [3–12].
Despite important papers, articles, and books published in the area of electric power
quality, its definition has not been universally agreed upon. However, nearly everybody
accepts that it is a very important aspect of power systems and electric machinery with
direct impacts on efficiency, security, and reliability. Various sources use the term “power
quality” with different meaning. It is used synonymously with “supply reliability,” “service quality,” “voltage quality,” “current quality,” “quality of supply,” and “quality of
consumption.”
Judging by the different definitions, power quality is generally meant to express
the quality of voltage and/or the quality of current and can be defined as: the measure,

analysis, and improvement of the bus voltage to maintain a sinusoidal waveform at rated
voltage and frequency. This definition includes all momentary and steady-state
phenomena.

1.2 CAUSES OF DISTURBANCES IN POWER SYSTEMS
Although a significant literature on power quality is now available, most engineers,
facility managers, and consumers remain unclear as to what constitutes a power
quality problem. Furthermore, due to the power system impedance, any current (or
voltage) harmonic will result in the generation and propagation of voltage (or current)
harmonics and affects the entire power system. Figure 1.1 illustrates the impact of current harmonics generated by a nonlinear load on a typical power system with
linear loads.


Introduction to Power Quality

harmonic voltage distortion at PCC due to propagation of
harmonic currents through the system impedance
sinusoidal
source voltage

customer with linear and nonlinear loads

system impedance
(e.g., cables, lines,
& transformers)

point of common
coupling (PCC)

nonlinear loads (e.g., switched-mode

power supplies, AC drives, fluorescent
lamps) drawing nonsinusoidal currents
from a perfectly sinusoidal voltage source
linear loads

customers with linear loads

harmonic voltage
distortion imposed
on other customers

Figure 1.1 Propagation of harmonics (generated by a nonlinear load) in power systems.

What are the origins of the power quality problem? Some references [9] divide the
distortion sources into three categories: small and predictable (e.g., residential consumers
generating harmonics), large and random (e.g., arc furnaces producing voltage fluctuations and flicker), and large and predictable (e.g., static converters of smelters and highvoltage DC transmission causing characteristic and uncharacteristic harmonics as well as
harmonic instability). However, the likely answers to the question are these: unpredictable events, the electric utility, the customer, and the manufacturer.
Unpredictable Events

Both electric utilities and end users agree that more than 60% of power quality problems
are generated by natural and unpredictable events [6]. Some of these include faults, lightning surge propagation, resonance, ferroresonance, and geomagnetically induced currents (GICs) due to solar flares [13]. These events are considered to be utility related
problems.
The Electric Utility

There are three main sources of poor power quality related to utilities:
• The point of supply generation. Although synchronous machines generate nearly perfect
sinusoidal voltages (harmonic content less than 3%), there are power quality problems
originating at generating plants which are mainly due to maintenance activity,
planning, capacity and expansion constraints, scheduling, events leading to forced
outages, and load transferring from one substation to another.

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Power Quality in Power Systems and Electrical Machines

• The transmission system. Relatively few power quality problems originate in the transmission system. Typical power quality problems originating in the transmission system
are galloping (under high-wind conditions resulting in supply interruptions and/or
random voltage variations), lightning (resulting in a spike or transient overvoltage),
insulator flashover, voltage dips (due to faults), interruptions (due to planned outages
by utility), transient overvoltages (generated by capacitor and/or inductor switching,
and lightning), transformer energizing (resulting in inrush currents that are rich in harmonic components), improper operation of voltage regulation devices (which can lead
to long-duration voltage variations), slow voltage variations (due to a long-term variation of the load caused by the continuous switching of devices and load), flexible AC
transmission system (FACTS) devices [14] and high-voltage DC (HVDC) systems [15],
corona [16], power line carrier signals [17], broadband power line (BPL) communications [18], and electromagnetic fields (EMFs) [19].
• The distribution system. Typical power quality problems originating in the distribution
system are voltage dips, spikes, and interruptions, transient overvoltages, transformer
energizing, improper operation of voltage regulation devices, slow voltage variations,
power line carrier signals, BPL, and EMFs.
The Customer

Customer loads generate a considerable portion of power quality problems in today’s
power systems. Some end-user related problems are harmonics (generated by nonlinear
loads such as power electronic devices and equipment, renewable energy sources,
FACTS devices, adjustable-speed drives, uninterruptible power supplies (UPS), fax
machines, laser printers, computers, and fluorescent lights), poor power factor (due to
highly inductive loads such as induction motors and air-conditioning units), flicker (generated by arc furnaces [20]), transients (mostly generated inside a facility due to device
switching, electrostatic discharge, and arcing), improper grounding (causing most

reported customer problems), frequency variations (when secondary and backup power
sources, such as diesel engine and turbine generators, are used), misapplication of technology, wiring regulations, and other relevant standards.
Manufacturing Regulations

There are two main sources of poor power quality related to manufacturing regulations:
• Standards. The lack of standards for testing, certification, sale, purchase, installation, and
use of electronic equipment and appliances is a major cause of power quality problems.
• Equipment sensitivity. The proliferation of “sensitive” electronic equipment and
appliances is one of the main reasons for the increase of power quality problems.
The design characteristics of these devices, including computer-based equipment, have
increased the incompatibility of a wide variety of these devices with the electrical
environment [21].


Introduction to Power Quality

Power quality therefore must necessarily be tackled from three fronts, namely:
• The utility must design, maintain, and operate the power system while minimizing
power quality problems;
• The end user must employ proper wiring, system grounding practices, and state-ofthe-art electronic devices; and
• The manufacturer must design electronic devices that keep electrical environmental
disturbances to a minimum and that are immune to anomalies of the power supply line.

1.3 CLASSIFICATION OF POWER QUALITY ISSUES
To solve power quality problems it is necessary to understand and classify this relatively
complicated subject. This section is based on the power quality classification and information from references [6] and [9].
There are different classifications for power quality issues, each using a specific property
to categorize the problem. Some of them classify the events as “steady-state” and “nonsteady-state” phenomena. In some regulations (e.g., ANSI C84.1 [22]) the most important
factor is the duration of the event. Other guidelines (e.g., IEEE-519) use the wave shape
(duration and magnitude) of each event to classify power quality problems. Other standards

(e.g., IEC) use the frequency range of the event for the classification.
For example, IEC 61000-2-5 uses the frequency range and divides the problems into
three main categories: low frequency (<9 kHz), high frequency (>9 kHz), and electrostatic discharge phenomena. In addition, each frequency range is divided into “radiated”
and “conducted” disturbances. Table 1.1 shows the principal phenomena causing electromagnetic disturbances according to IEC classifications [9]. All these phenomena are
considered to be power quality issues; however, the two conducted categories are more
frequently addressed by the industry.
The magnitude and duration of events can be used to classify power quality events, as
shown in Fig. 1.2. In the magnitude–duration plot, there are nine different parts [11].
Various standards give different names to events in these parts. The voltage magnitude
is split into three regions:
• interruption: voltage magnitude is zero,
• undervoltage: voltage magnitude is below its nominal value, and
• overvoltage: voltage magnitude is above its nominal value.
The duration of these events is split into four regions: very short, short, long, and very
long. The borders in this plot are somewhat arbitrary and the user can set them according
to the standard that is used.
IEEE standards use several additional terms (as compared with IEC terminology) to
classify power quality events. Table 1.2 provides information about categories and characteristics of electromagnetic phenomena defined by IEEE-1159 [23]. These categories
are briefly introduced in the remaining parts of this section.

7


Power Quality in Power Systems and Electrical Machines

very short
overvoltage
magnitude of event

8

short
overvoltage

long
overvoltage

very long
overvoltage

110%
normal operating voltage
90%

very short
undervoltage

short
undervoltage

1-3 cycles

long
undervoltage

1-3 min

very long
undervoltage

1-3 hours

duration of event

Figure 1.2 Magnitude-duration plot for classification of power quality events [11].
Table 1.1 Main Phenomena Causing Electromagnetic and Power Quality Disturbances [6,9]
Conducted low-frequency phenomena

Harmonics, interharmonics
Signaling voltage
Voltage fluctuations
Voltage dips
Voltage imbalance
Power frequency variations
Induced low-frequency voltages
DC components in AC networks
Radiated low-frequency phenomena

Magnetic fields
Electric fields
Conducted high-frequency phenomena

Induced continuous wave (CW) voltages or currents
Unidirectional transients
Oscillatory transients
Radiated high-frequency phenomena

Magnetic fields
Electric fields
Electromagnetic field

Steady-state waves
Transients
Electrostatic discharge phenomena (ESD)

Nuclear electromagnetic pulse (NEMP)


Introduction to Power Quality

1.3.1 Transients
Power system transients are undesirable, fast- and short-duration events that produce distortions. Their characteristics and waveforms depend on the mechanism of generation
and the network parameters (e.g., resistance, inductance, and capacitance) at the point
of interest. “Surge” is often considered synonymous with transient.
Transients can be classified with their many characteristic components such as amplitude, duration, rise time, frequency of ringing polarity, energy delivery capability, amplitude spectral density, and frequency of occurrence. Transients are usually classified into
two categories: impulsive and oscillatory (Table 1.2).
Table 1.2 Categories and Characteristics of Electromagnetic Phenomena in Power Systems as Defined
by IEEE-1159 [6,9]
Typical
spectral
Typical
Typical voltage
content
duration
magnitude
Categories

1. Transient

1.1. Impulsive
• nanosecond

• microsecond
• millisecond
1.2. Oscillatory
• low frequency
• medium
frequency
• high frequency
2. Short-duration 2.1. Instantaneous
• interruption
variation
• sag
• swell
2.2. Momentary
• interruption
• sag
• swell
2.3. Temporary
• interruption
• sag
• swell
3. Long-duration 3.1. Sustained
variation
interruption
3.2. Undervoltage
3.3. Overvoltage
4. Voltage
imbalance

5 ns rise
1 μs rise

0.1 ms rise

<50 ns
50 ns–1 ms
>1 ms

<5 kHz
5–500 kHz
0.5–5 MHz

0.3–50 ms
20 μs
5 μs

0–4 pu
0–8 pu
0–4 pu

0.5–30 cycles <0.1 pu
0.5–30 cycles 0.1–0.9 pu
0.5–30 cycles 1.1–1.8 pu
30 cycle–2 s
30 cycles–3 s
30 cycles–3 s

<0.1 pu
0.1–0.9 pu
1.1–1.4 pu

2 s–2 min

3 s–1 min
3 s–1 min

<0.1 pu
0.1–0.9 pu
1.1–1.2 pu

>1 min

0.0 pu

>1 min
>1 min
steady state

0.8–0.9 pu
1.1–1.2 pu
0.5–2%
Continued

9


Power Quality in Power Systems and Electrical Machines

Table 1.2 Categories and Characteristics of Electromagnetic Phenomena in Power Systems as Defined
by IEEE-1159—cont'd
Typical
spectral
Typical

Typical voltage
Categories
content
duration
magnitude

5. Waveform
distortion

5.1.
5.2.
5.3.
5.4.
5.5.

6. Voltage
fluctuation
7. Power frequency
variations

DC offset
Harmonics
Interharmonics
Notching
Noise

0–100th
0–6 kHz
Broadband
<25 Hz

steady state
steady state
steady state
steady state
steady state
intermittent

0–0.1%
0–20%
0–2%
0–1%
0.1–7%

<10 s

An impulsive transient is a sudden frequency change in the steady-state condition of
voltage, current, or both that is unidirectional in polarity (Fig. 1.3). The most common
cause of impulsive transients is a lightning current surge. Impulsive transients can excite
the natural frequency of the system.
An oscillatory transient is a sudden frequency change in the steady-state condition of
voltage, current, or both that includes both positive and negative polarity values. Oscillatory transients occur for different reasons in power systems such as appliance switching,
capacitor bank switching (Fig. 1.4), fast-acting overcurrent protective devices, and
ferroresonance (Fig. 1.5).

12

10

8

current (kA)

10

6

4

2

0
5

10

15

20

time (µs)

Figure 1.3 Impulsive transient current caused by lightning strike, result of PSpice simulation.