Power System

Harmonics
Course Code: 4EL402
Mrs. Seema P. Diwan

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 Course: Power System Harmonics
(4EL402)
• Prerequisite: Power system
Engineering and Power electronics

• Assessment:
–20 marks T1
–20 marks T2
–60 marks ESE
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 Course Objectives :

This course is intended to provide basic knowledge of

causes, consequences and solutions of power quality
problems that affect the operation of computerized
processes and electronic systems.
It also aims to provide a theoretical background to correctly
approach the problem of reactive, harmonic and unbalance
compensation, in the context of the applicable power
theory. 

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 Course Learning Outcomes:
CO After completion of the course the Bloom’s Cognitive
student will be able to level Descriptor

Explain the basic concepts of Power Quality disturbances ,

power definitions and other figures of merit under distorted
CO1
operation.

Apply various definitions of power components for Single

CO2 Phase and Three Phase circuits to analyze figures of merit
in harmonic environments..
To Design and evaluate the performance of harmonic
CO3 filters to mitigate power quality problems.

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Module Module Contents Hours
Introduction to Power Quality
What is Power Quality?,Power Quality -- Voltage Quality, Why Are We Concerned About Power Quality, Power
Quality standards, General Classes of Power Quality Problems, Transients, Long-Duration Voltage Variations,
I Short-Duration Voltage Variations, Voltage Imbalance, Waveform Distortion 4
Voltage Fluctuation, Power Frequency Variations, Power Quality Terms

Fundamentals of Harmonics
Harmonic Distortion, Voltage versus Current Distortion, Harmonics versus Transients, Harmonic Indexes,
Harmonic Sources from Commercial Loads, Harmonic Sources from Industrial Loads, Locating Harmonic
II Sources, System Response Characteristics, Effects of Harmonic Distortion, Interharmonics, Parallel resonance, 6
case study on parallel resonance.

Harmonic Mitigation Techniques- Passive Filters

Shunt passive filters, types, Design considerations of single tuned filters, Detuned filters, Design considerations
III of Detuned filters, High pass filters, Design considerations of HP filters, Case studies and numerical examples 6

Harmonic Mitigation Techniques-Shunt Active Power Filters

Introduction, State of the Art on Shunt Active Power Filters, Classification of Shunt Active Power Filters,
Principle of, Operation and Control of Shunt Active Power Filters, Analysis and Design of Shunt Active Power
IV 4
Filters, Numerical Examples

Power Definitions in Single Phase Circuits

V Definitions of various powers, power factor and other figures of merit under sinusoidal and non-sinusoidal
conditions applicable to single phase circuits. 4

Power Definitions in Three Phase Circuits

Definitions of various powers, power factor and other figures of merit under balanced, unbalanced and non-
VI sinusoidal conditions. IEEE 1459 power definitions applicable to three phase circuits
4

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 Module - 1
Introduction to Power Quality

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 Major reasons for increased
concern about Power Quality
Reason 1:
Newer Generation load equipment, with
microprocessor based controls and power
electronic devices, is more sensitive to
power quality variations than was
equipment used in the past.

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LOADS
Our power systems were designed for:

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Now the power system serves

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Disturbing loads

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Sensitive Loads

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Reason 2:
The increasing emphasis on overall power
system efficiency has resulted in
continued growth in the application of
devices such as high efficiency adjustable
speed drives and shunt capacitors for
power factor correction to reduce loss.
Result : Increase in harmonic levels.
Impact of increased harmonic level is
point of concern.
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Reason 3:
Many things are interconnected in the
network. Integrated processes means that
failure of any component has more
important consequence.

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 Classical Distribution Systems

PQ TUTORIAL: PART I 14/57

 Future Distribution Systems

PQ TUTORIAL: PART I 15/57

Future Distribution system

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Causes of Power Quality Failures

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 Power Quality Definitions
•Power quality is defined in many resources, which give
different meaning to different people and sometimes
conflicting statements of power quality due to a lot of
confusion on the meaning of the term power quality
•Therefore, its definition has not been universally agreed
upon.
•It is used synonymously with supply reliability, service
quality, voltage quality, quality of supply, and quality of
consumption.
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•There can be completely different definitions for power
quality, depending on one’s frame of reference.
•For example, a utility may define power quality as reliability
and show statistics demonstrating that its system is 99.98
percent reliable. Criteria established by regulatory agencies are
usually in this vein.
•A manufacturer of load equipment may define power quality
as those characteristics of the power supply that enable the
equipment to work properly. These characteristics can be very
different for different criteria.
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The definition of power quality given in the IEEE
dictionary states that
• “Power quality is the concept of powering
and grounding sensitive equipment in a
manner that is suitable to the operation of that
equipment.”

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•The IEC definition of power quality, given in IEC
61000-4-30, states
•“Characteristics of the electricity at a given
point on an electrical system, evaluated against
a set of reference technical parameters.”

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•Electromagnetic compatibility is a term related to
power quality used in IEC 61000-1-1, which states
that
•“Electromagnetic compatibility is the ability of an
equipment or system to function satisfactorily in
its electromagnetic environment without
introducing intolerable electromagnetic
disturbances to anything in that environment.”
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•Power quality is ultimately a consumer-driven
issue, and the end user’s point of reference takes
precedence.
Therefore, the following definition of a power
quality problem is used
“Any power problem manifested in voltage,
current, or frequency deviations that results in
failure or mis-operation of customer equipment.”
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 The cost of Power Quality

a. One glass plant estimates that a five-cycle interruption, a momentary

interruption less than a tenth of a second, can cost about $200,000.
b. A major computer center reports that a 2-s interruption can cost some
$600,000.
c. In some factories, following a voltage sag, the restarting of assembly
lines may require clearing the lines of damaged work, restarting of boilers,
and reprogramming automatic controls at a typical cost of $50,000 per
incident.
d. One automaker estimated that total losses from momentary power
interruptions at all its plants run to about $10 million a year.

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Why is Power Quality Important?

• It affects both utilities as

suppliers and customers as
users

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 Impact on Customer Side
• Computers and communication equipment are
susceptible to power system disturbances
which can lead to loss of data and erratic
operation.
• Automated manufacturing processes such as
paper – making machinery, chip-making
assembly lines ,etc. can shutdown in case of
even short voltage sags

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Induction and synchronous machines can have excessive
losses and heating.
 Impact on Customer Side (Cont.)
• Home electronic equipment are vulnerable to power
quality problems-e.g., blinking VCR (Video-Cassette
Recorder) machines and digital clocks.
• Equipment and process control malfunction
translates to dollars of expense for replacement parts
and for down time ,impacting adversely on
profitability and product quality.

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 Impact on Utility Side
• Increased losses in cables , transformers and
conductors, especially neutral wires.
• Errors in energy meters , which are calibrated
to operate under sinusoidal conditions.

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Failure of power –factor correction capacitors due to
resonance conditions.
 Impact on Utility Side (Cont.)
• Interference with ripple control and power line
carrier systems used for remote switching, load
control,etc.
• Unhappy customers as well as malfunction and
failure of system components and control systems,
impacting adversely on profitability.

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 Incorrect operation of protective relays,
particularly in solid-state and
microprocessor controlled systems.

Mal-operation Nuisance tripping

Trip level set lower than the fundamental value. Trip level set higher than the fundamental value.
The relay should trip as the fundamental value The relay should not trip as the fundamental
is higher than the trip level. But the presence of value is lower than the trip level. But the presence
harmonics has reduced the peak value. Hence of harmonics has increased the peak value. Hence
the protective relay will not trip. the protective relay will trip.
 Power Quality Standards
In view of these power pollution problems, a number of
organizations such as IEC, IEEE, American National
Standards Institute (ANSI), British Standards (BS),
European Norms (EN), Computer Business Equipment
Manufacturers Association (CBEMA), and Information
Technology Industry Council (ITIC) have developed different
standards to specify the permissible limits of various
performance indices to maintain the level of power quality
to an acceptable benchmark and to provide guidelines to
the customers, manufactures, and utilities on curbing the
various events causing the power quality problems.

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 Classification of Power Quality
• Terminology for describing power quality
phenomenon.
• Classification
– Steady state vs non-steady state
– Based on the duration of the event
– Duration and magnitude
– Frequency range

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IEC 61000

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ANSI Standard C84

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IEEE 519

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IEEE 1159

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Categories and Characteristics of Power System
Electromagnetic Phenomena

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 Power Disturbance:
• Any deviation from the normal value of the input.
• Harmonic , noise , notching
• Transient
• Under voltage
• Overvolatge
• Swell
• Sag (dip)
• Interruption

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Voltage Quality within Utility Distribution
Event that is undesirable and momentary
in nature.
Transients – very quick < 1 cycle
– Normal cause is lightning strike
– No lights flicker
– Utilities employs lightning arrestors at substations
and at primary switches located at each building
electric service equipment
– End users need to purchase/install TVSS equipment
to further clamp the voltage spike.

( TVSS : transient voltage surge

suppressor ) 43
Impulsive Transient

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 Oscillatory Transient

An oscillatory transient is a sudden, non power frequency

change in the steady-state condition of voltage, current,
or both that includes both positive and negative polarity
values.

• An oscillatory transient consists of a voltage or current whose

instantaneous value changes polarity rapidly.
• It is described by spectral content, duration and magnitude..

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 Classification
oscillatory
transient

Medium
High Frequency Low Frequency
Frequency
Transient Transient
Transient

Spectral Between 5 and

content-greater Less than 5 kHz
500 kHz
than 500kHz
Duration-
In microseconds ie 10s of
0.3 to 50 ms
several cycles of microseconds
principle frequency

Cause: Back to back

Capacitor bank
Local system response to capacitor
energization and
impulsive transient energization and ferroresonance 47
cable switching
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 Voltage Quality

• Long term voltage Variations

Long duration variations encompass root-mean-square (rms) deviations at
power frequency for longer than 1 min.
– As load increases, voltage drops (and vice versa)
– Utilities compensates the long-duration voltage variations through
the use of automatic load tap changers at the substation
– System voltage tolerance limits are set in ANSI C84.1. The system
voltages are designed to always operate in the range limits (108 –
126V)
--Long duration voltage variation can be either overvoltage or under
voltage.
- It is not the result of fault on the system. But as a consequence of
load variation.
- Displayed as plots of rms voltage verses time

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 Overvoltage
An overvoltage is an increase in the rms ac voltage
greater than 110 percent at the power frequency for
a duration longer than 1 min.
• Overvoltages are usually the result of load switching
(e.g., switching off a large load or energizing a
capacitor bank).
• The overvoltages result because either the system is
too weak for the desired voltage regulation or
voltage controls are inadequate.
• Incorrect tap settings on transformers can also result
in system overvoltages.
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Overvoltage

Duration:> 1min
Magnitude:1.1- 53
1.2pu
 Undervoltage

An undervoltage is a decrease in the rms ac voltage to less

than 90 percent at the power frequency for a duration longer
than 1 min

• Undervoltages are the result of switching events that are the

opposite of the events that cause overvoltages.

• A load switching on or a capacitor bank switching off can cause

an undervoltage until voltage regulation equipment on the
system can bring the voltage back to within tolerances.
Overloaded circuits can result in undervoltages also.

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Undervoltage

Duration >1min
Magnitude: 0.8-0.9pu
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 Sustained Interruptions
• When the supply voltage has been zero for a period of time in
excess of 1 min, the long-duration voltage variation is
considered a sustained interruption
-Voltage interruptions longer than 1 min are often permanent and require
human intervention to repair the system for restoration.
-The term sustained interruption refers to specific power system phenomena
and, in general, has no relation to the usage of the
term outage.
-Outage, as defined in IEEE Standard 100, does not refer to a specific
phenomenon, but rather to the state of a component in a system that has
failed to function as expected.
-Also, use of the term interruption in the context of power quality monitoring
has no relation to reliability or other continuity of service statistics. Thus, this
term has been defined to be more specific regarding the absence of voltage for
long periods. 56
 Short Duration Voltage Variations
• This category encompasses the IEC category of voltage dips
and short interruptions. Each type of variation can be
designated as instantaneous, momentary, or temporary,
depending on its duration.
• Short-duration voltage variations are caused by
• fault conditions
• the energization of large loads which require high
starting currents
• intermittent loose connections in power wiring.
• The fault can cause either temporary voltage drops (sags),
voltage rises (swells), or a complete loss of voltage
(interruptions).

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Voltage Quality within Utility
Distribution

Sags / Swells
– Voltage imbalance lasting from 3-20 cycles
– Typical cause switching on the incoming by high
voltage transmission line
– Lights flickering are indicative of this fault
– Utilities does not protect for this condition

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Variation voltage magnitudes and duration IEEE 1159

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 Voltage Sag
A sag is a decrease to between 0.1 and 0.9 pu in rms voltage
or current at the power frequency for durations from 0.5 cycle
to 1 min.

• 20 percent sag will be considered an event during which the rms

voltage decreased by 20 percent to 0.8 pu.
• Voltage sags are usually associated with system faults but can
also be caused by energization of heavy loads or starting of
large motors.
• Effects:
• Duration-dependent
• Failure of computer equipment
• Outages of sensitive process plants

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 Voltage Sags
• Effects:
– Duration-dependent
– Failure of computer equipment
– Outages of sensitive process plants

• Measures
– CBEMA Curve (1978): less stringent restrictions
– ITIC Curve (1996): demands more severe
performance standards

64/57
Sag or Dip

Duration:3s-1min
Magnitude:0.1-
0.9pu 65
Process Solenoid Relay & Contactor Operated
Devices that can “trip” with
25% Voltage Sag Events

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 Voltage Swell
A 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.

• Swells are characterized by their magnitude (rms value) and

duration.
• The severity of a voltage swell during a fault condition is a
function of the fault location, system impedance, and grounding.
• Swell can occur :
• temporary voltage rise on the unfaulted phases during an SLG
fault.
• switching off a large load or energizing a large capacitor bank.

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 Swell

Duration:3s-1min
Magnitude: 1.1- 68
1.2pu
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 Voltage Imbalance
Voltage imbalance (also called voltage unbalance) is sometimes
defined as the maximum deviation from the average of the three-
phase voltages or currents, divided by the average of the three-
phase voltages or currents, expressed in percent.
OR
The ratio of either the negative- or zero sequence component to
the positive-sequence component can be used to specify the
percent unbalance

• Voltage unbalance can also be the result of blown fuses in one

phase of a three-phase capacitor bank.
• Severe voltage unbalance (greater than 5 percent) can result
from single-phasing conditions.

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 Waveform Distortion
Waveform distortion is defined as a steady-state deviation from
an ideal sine wave of power frequency principally characterized
by the spectral content of the deviation

There are five primary types of waveform distortion:

■ DC offset
■ Harmonics
■ Interharmonics
■ Notching
■ Noise

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 DC Offset
The presence of a dc voltage or current in an ac power system
is termed dc offset

Cause:
• Asymmetry of electronic power converters.
• Incandescent light bulb life extenders, for example, may consist
of diodes that reduce the rms voltage supplied to the light bulb
by half-wave rectification.

Effect:
• Detrimental effect by biasing transformer cores so they
saturate in normal.
• Additional heating and loss of transformer life
• Electrolytic erosion of grounding electrodes and other
connectors 72
 Harmonics
Harmonics are sinusoidal voltages or currents having
frequencies that are integer multiples of the frequency at
which the supply system is designed to operate (50 to 60 Hz)
Cause:
• nonlinear characteristics of devices and loads on the power
system.
Harmonic indices:
Harmonic distortion levels are described by the complete harmonic
spectrum with magnitudes and phase angles of each individual
harmonic component.
• The total harmonic distortion (THD), is a measure of the effective
value of harmonic distortions.
• The total demand distortion (TDD) is the same as the total
harmonic distortion except that the distortion is expressed as a
percent of some rated load current rather than as a percent of the
fundamental current magnitude at the instant of measurement.
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 Interharmonics
Voltages or currents having frequency components that are not
integer multiples of the frequency at which the supply system
is designed to operate (e.g., 50 or 60 Hz) are called
interharmonics
Cause:
• It is generally the result of frequency conversion . It varies with
load.
• static frequency converters, cycloconverters, induction
furnaces, and arcing devices.

Effect:

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 Notching
Notching is a periodic voltage disturbance caused by the
normal operation of power electronic devices when current is
commutated from one phase to another.
• Notching is characterised by the harmonic spectrum of the
affected voltage.
• Higher order frequencies are associated with notching.
• The notches occur when the current commutates from one
phase to another. During this period, there is a momentary
short circuit between two phases, pulling the voltage as close
to zero as permitted by system impedances.

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 Noise
Noise is defined as unwanted electrical signals with broadband
spectral content lower than 200 kHz superimposed upon the
power system voltage or current in phase conductors, or found
on neutral conductors or signal lines.

Cause:
• Noise in power systems can be caused by power electronic
devices, control circuits, arcing equipment, loads with solid-
state rectifiers, and switching power
• Noise problems are often exacerbated by improper grounding
that fails to conduct noise away from the power system.

Effect:
• Noise disturbs electronic devices such as microcomputer and
programmable controllers..
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 Noise

Duration: steady
state
Magnitude: 0-1% 77
 End of module one. Any questions?

• END OF MODULE ONE

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