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International Journal of Science, Engineering and Technology Research (IJSETR), Volume 3, Issue 2, February 2014

Review of Causes and Effect of Harmonics on

Power System
Manish Kumar Soni, Nisheet Soni

frequency f,2f,3f,4f,5f.Even harmonics are

Abstract This paper is intended to give an overview of 2f,4f,6f,8fand odd harmonics are f,3f,4f,5f,7f... Generally
harmonic distortion in power system. The pure sinusoidal
waveform generated by electrical utilities is distorted by the even harmonics get cancelled because of their symmetrical
harmonics produced by the increased use of non linear loads. nature but odd harmonics should be eliminated by some
As saving of electrical energy is the main target of industrial
filtering or compensation techniques.
consumer and also utility, the use of energy efficient non linear
equipment increases rapidly. The modern industrial system
increases use of non linear loads as the control becomes simple, The harmonic distortion is caused by nonlinear devices in
more efficient, accurate and widely available. However, it gives which the current is not proportional to the applied voltage.
rise to more distortions in current and voltage waveforms on Figure 1 illustrate the sinusoidal applied voltage to a simple
the ac power systems and pollutes the system. Here a survey is nonlinear resistor in which the applied voltage and current
made to show details of causes and effect of harmonics present vary according to curve shown. While the applied voltage is
in various types of non linear loads. perfectly sinusoidal but the resulting current is distorted. By
increasing the voltage by a small percentage the current is
double and take a different waveform.
Index Terms Harmonics, Non linear loads, THD, TDD,
Harmonic Distortion.

The main objective of the electric utility is to deliver
sinusoidal voltage at constant magnitude throughout their
system. This objective is complicated by the fact that there
are loads on the system that produce harmonic currents.
These currents result in distorted voltages and currents that
can adversely affect the performance of power system in
different ways. As the number of harmonic producing loads
has increased over the years, it has become necessary to
address their influence when making any additions or
changes to an installation. To fully appreciate the impact of
these phenomena, there are two important concepts to bear in
mind with regard to power system harmonics. The first is the
nature of harmonic-current producing loads (non-linear
loads) and the second is the way in which harmonic currents
flow and how the resulting harmonic voltages develop.

A harmonic component in a power system is defined as

the sinusoidal component of a periodic waveform that has a Fig.1. A non linear load drawing current in short pulses
frequency equal to an integer multiple of the fundamental
frequency of the system. It is given by, Fh =h* Fundamental
frequency, where h is the integer to be multiplied. If the Figure 2 illustrate that any periodic distorted waveform can
fundamental frequency is f, then the harmonics have be expressed by sum of sinusoids of different frequencies in
which the frequency of each sinusoids is integer multiple of
fundamental frequency. This integer multiple is called
Manuscript received Jan 11, 2014.
harmonic component of fundamental. When both positive
and negative half cycle have identical wave shape the fourier
Manish Kumar Soni, Electrical Engg Dept., Shri Ram Institute of series contains only odd harmonics. This offers
Technology ., Jabalpur, India, 9907974849 simplifications for study of power system most harmonic
Nisheet Soni EEE Department,., Shri Ram Institute of Technology .,
Jabalpur, India, producing devices have both polarities.

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B) Harmonics originated at medium voltages by large

industrial loads like Traction equipment, variable speed
drives, Thyristor controlled drives, Induction Heaters,
Arc furnaces, Arc welding, Capacitor bank, electronic
energy controllers.

C) Harmonic originated at low voltages by consumer end like

single phase loadings, uninterrupted power supplier,
semiconducting devices, CFL, Solid state devices,
domestic appliances and accessories using electric
devices, electronic fluorescent chokes, electronic fan
regulator , light dimmers.


Fig.2 : Fourier series representation of a distorted waveform

Utility supplies generally pure sinusoidal voltage to the users.
The current wave forms of the systems connected to the
utility will be sinusoidal only if a linear load like
Usually, the higher-order harmonics (range from 25th to Incandescent bulbs connected to it. However this is not
50th) are negligible. While it may cause interference with practically possible due to the increased use of nonlinear
low power electronic devices, but not damaging to the power loads like PCs, UPS, Laser printers, microwave ovens,
system. It is also difficult to collect sufficiently accurate data electronic ballast, process control systems etc. This is due to
to model power systems at these frequencies because of the the non linear characteristic of devices used in equipments
occurance of resonance in the system in this frequency drawing current waveform that doesnt follow the voltage
range. These resonances can be excited by notching or waveform.
switching transients in electronic power converters. This
causes voltage waveforms with multiple zero crossings The total current drawn by the non linear loads is given by.
which disrupt timing circuits. These resonances generally
occur on systems with underground cable but no power factor IT = IF + IH
correction capacitors.
where IF = Fundamental current
If the power system is depicted as series and shunt IH = Total harmonic current.
elements, as is the conventional practice, the vast majority of
the nonlinearities in the system are found in shunt elements The circuit draws current only during the peaks of voltage
(i.e. loads). In transformers, also, the source of harmonics is wave form as shown in Figure 2, to charge the capacitor to
the shunt branch (magnetizing impedance) of the common the peak of the line voltage. This type of power supplies
"T" model; the leakage impedance is linear. Thus, the main drawing current in short pulses during voltage waveform
sources of harmonic distortion will ultimately be end-user peak has improved the efficiency of the equipment but at the
loads. This is not to say that all end users who experience cost of generating high frequency harmonics. Typical current
harmonic distortion will themselves have significant sources waveform of a PC measured at the power input is high
of harmonics, but that the harmonic distortion generally distortion in current waveform is observed.
originates with some end-user's load or combination of loads.
A. Harmonic Indices
There are two most commonly used harmonic indices
used for measuring the harmonic content of a waveform that
II. SOURCES OF HARMONICS are total harmonic distortion and total demand distortion.
Both measures the effective value of a waveform and may be
Harmonic distortion in power system is generally due to wide
applied to either voltage or current.
spread use of non linear loads. The sources of harmonics can
be broadly classified as follows: Total Harmonic Distortion (THD)

A) Harmonic originated at high voltages by supply The THD is a measure of the effective value of the
authorities. harmonic components of a distorted waveform. It is the
potential heating value of the harmonics with respect to the
1. HVDC systems
fundamental. This index can be used for either voltage or
2. Back to back systems current.
3. Static VAR compensation system.
4. Wind and solar power converters with interconnection.
ISSN: 2278 7798
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where MI, is the RMS value of harmonic component h of the

quantity M.

The THD is related to the RMS value of the waveform as



Fig4 : Variation of the voltage THD over a week period

The total harmonic distortion is very useful for many
application. It provides good idea for how much extra heat
generated when a distorted voltage is applied to a resistive
load. It also give indication of losses due to current flowing Where, IL is the peak load current at the fundamental
through conductor. But not a good indicator of the voltage frequency component measured at a point of common
stress within a capacitor because it is related to peak value of coupling (pcc) which is usually at the consumer metering
the voltage waveform. The THD is mostly used to describe point.
harmonic voltage distortion. Harmonic voltage are always
referenced to fundamental component of the waveform at the
sampling time. Because on varying the fundamental voltage
to few percent the voltage THD is nearly a meaningful

Variation of the total harmonic distortion over a time follow

a distinct pattern representing activity of non linear load in In an ideal power system voltage and current waveforms
the system. Figure shows harmonic distortion for a period of are purely sinusoidal. In practice, non sinusoidal currents
a week that is taken from 132 KV distribution substation. result when the current flowing through the load is non
Figure shows high distortion occurs at night and early linearly related to the applied voltage. In a simple circuit
morning hours since non linear loads are high as compared
containing only linear circuit elements (resistance,
to linear load during these hours.
inductance and capacitance), the current which flows is
proportional to the applied voltage. So that it results in a
Total demand distortion (TDD) sinusoidal current flow. The situation where the load is
simple full wave rectifier, current flows only when the supply
The current distortion can be characterized by THD value but
this can often misleading. A small current may have high voltage exceeds that stored on the reservoir capacitor. It says
THD value but not significant effect on system. Many that waveforms tend to distort from the sine wave and this is
adjustable speed drives will exhibit high THD for input the cause for harmonics [6]. Non-linear loads create
current when operating at light loads. This is not significant harmonics by drawing current in abrupt short pulses, rather
concern because magnitude of harmonic current is low even than in a smooth sinusoidal manner [7] as shown in the fig.1.
though current distortion is high.
High levels of harmonic distortion can cause several
Some analyst have attempted to avoid this difficulty by effects such as increased transformer, capacitor, motor or
referring total harmonic distortion to total demand distortion generator heating, false operation of electronic equipment,
that is fundamental of the peak demand load current and incorrect readings on meters, false operation of protective
serves as the basis for the guidelines in IEEE standard 519 relays, interference with telephone circuits etc. Since
1992 recommended practices and requirements for harmonic harmonic distortion is caused by nonlinear elements
control in power system.
connected to the power system, any device that has
non-linear characteristics will cause harmonic distortion.
Examples of common sources of power system harmonics,
some of which never cause serious problems, are:
transformer saturation and inrush, transformer neutral
connections, MMF distribution in AC rotating machines,

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electric arc furnaces, fluorescent lighting, computer switch based equipment needs single phase full wave diode
mode power supplies, battery chargers, imperfect AC rectifier bridge for DC power supply.
sources, variable frequency motor drives (VFD), inverters,
There are two common techniques used for single phase
and television power supplies.
supply. One uses ac voltage control methods in which
transformer is used to reduce the voltage required for DC bus.
The inductance of the transformer provides benefits of
V. NON LINEAR LOADS smoothing the input current waveform. The second
technology uses switched mode power supply for dc to dc
Due to the changes in the operating conditions and the rapid conversion to get smooth dc output. The ac line is directly
connected to input diode bridge which eliminates
growth of advanced power conversion devices, electronics
transformer. The output dc regulated voltage on the capacitor
equipments, computers, office automation, air-conditioning is converted back to high frequency ac voltage by high speed
systems, adjustable speed heating ventilation can cause switches and again rectified. Personal computers, copiers,
current distortions. This is due to increase in harmonics printers and other single phase electronic devices employ
drastically. According to the Electric Power Research (EPR) switched mode power supplies. The advantages of switched
in 1995, 35-40% of all electric power flows through mode power supplies are compact size, light weight, efficient
electronic converters. This is expected to increase to 85% by operation and no need of transformers. The switched mode
powers supply can tolerate large variation in input voltage.
the year 2012. All these devices are named as non linear
loads and become sources of harmonics.



A. Harmonic Sources From Commercial load

Commercial facilities such as office complexes, hospitals,
internet data centres are dominated with high efficiency
fluorescent lightning with electronic ballasts, adjustable
speed drives for heating, ventilation and air conditioning
loads sensitive electronic equipment and elevator drives Fig 5 : Switch mode power supply
supplied by single phase switch mode power supplies.
Commercial loads are characterized by large number of The switched mode power supply rich in third harmonic
small harmonic producing loads. Depending on the diversity current. The third harmonic currents are additive nature in
of load these small harmonic current may add or cancel each neutral of the three phase system so it causes increasing
other. The voltage distortion depends on the circuit concern in overloading of the neutral conductors specially in
impedance and harmonic current. The power factor older building where undersized neutral has been installed.
correcting equipments are not used in commercial facility so There is also transformer overheating problem due to
the circuit impedance is dominated by transformer and harmonic current, stray flux and high neutral current.
conductor impedance. Therefore voltage distortion can be
calculated by multiplying the harmonic current by circuit
impedance. Different non linear loads with their
characteristics are described in following sections.

Single-phase power supplies

Electronic power converter loads such as adjustable

speed drives, electronic power supplies, dc motor drives,
battery chargers, electronic ballasts and many other
rectifier and inverter are the most important class of non
linear loads because of their capacity of producing
harmonic currents. A major concern is in the single phase Fig 6 : Switch mode power supply current
electronic equipments that produces too much harmonic
current. The percentage of load contains electronic power
supplies increases with the increased use of personal Fluorescent Lightning
computers. The modern electronic and microprocessor

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Lighting typically accounts for 40 to 60 percent of a harmonic currents. This is a great advantage because the
commercial building load. According to the 1995 third harmonic current is the largest component of
Commercial Buildings Energy Consumption study harmonics. However, they can still be significant source of
conducted by the U.S. Energy Information Administration, harmonics at their characteristic frequencies.
fluorescent lighting was used on 77 percent of commercial
floor spaces, while only 14 percent of the spaces used
incandescent lighting.' Fluorescent lights are a popular
choice for energy savings.

Fluorescent lights are discharge lamps; it require a ballast

to provide a high initial voltage to initiate the discharge for
the electric current to flow between two electrodes in the
fluorescent tube. Once the discharge in the tube is
established, the voltage decreases as the arc current
increases. It is essentially a short circuit between the two Fig 7 : Current spectrum for CSI type ASD
electrodes, and the ballast has to quickly reduce the current to
a level to maintain the specified lumen output. Thus, a ballast
is also a current limiting device in lighting applications.
Saturable devices
There are two types of ballasts namely magnetic and
electronic. The magnetic ballast is simply made up of an Transformers and other electromagnetic devices with a
iron-core transformer with a capacitor encased in an steel core, including motors come on this category.
insulating material. A single magnetic ballast can drive one Harmonics are generated due to the nonlinear magnetizing
or two fluorescent lamps and it operates at fundamental characteristics of the steel ( Fig.8).
frequency, i.e., 50Hz. The iron-core magnetic ballast causes
additional heat losses which makes it inefficient as compared Power transformers are designed normally to operate
to an electronic ballast. just below the "knee" point of the magnetizing saturation
curve. The operating flux density of a transformer is selected
An electronic ballast employs a switch mode type power based on a complicated optimization of steel cost, no-load
supply to convert the fundamental frequency voltage to a losses, noise, and numerous other factors. Many electric
much higher frequency voltage typically in the range of 25 to utilities will penalize transformer vendors by various
40 kHz. This high frequency has two advantages. First, a amounts for no-load and load losses, and the vendor will try
small inductor is sufficient to limit the arc current. Second, to meet the specification with a transformer that has the
the high frequency eliminates or greatly reduces flickering lowest evaluated cost. A high-cost penalty on the no-load
associated with an iron core magnetic ballast. losses or noise will generally result in more steel in the core
and a higher saturation curve that yields lower harmonic
B. Harmonic Sources From Industrial loads currents.

In Modern industry there are wide spread application of

nonlinear loads. These non linear loads inject harmonic
currents into the power system that causes harmonic
distortion in the voltage. These nonlinear loads have a
relatively low power factor. To improve the power factor
industrial facilities often utilize capacitor banks to avoid
penalty charges. The application of power factor correction
capacitors can potentially magnify harmonic currents from
the nonlinear loads, giving rise to resonance conditions
within the facility. The highest voltage distortion level usu-
ally occurs at the facility's low-voltage bus where the
capacitors are applied. Resonance conditions cause motor Fig 8: Transformer magnetizing characteristic
and transformer overheating, and maloperation of sensitive
electronic equipment.
Although transformer exciting current is rich in
harmonics at normal operating voltage it is typically less
than 1 percent of rated full load current. However, their effect
will be noticeable on utility distribution systems where there
Three phase power electronic converters are hundreds of transformer. It is common to notice a signifi-
cant increase in triplen harmonic currents during the early
Three phase power electronic converters differ from morning hours when the load is low and the voltage rises. At
single-phase converters because they do not generate third this condition transformer exciting current is more visible
because there is insufficient load to obscure it and the

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increased voltage causes more current to be produced.

Harmonic voltage distortion from transformer over
excitation is generally apparent only under the light load

Some transformers are operated in the saturation region.

One example is a triplen transformer which is used to
generate 180 Hz for induction furnace. Motors also exhibit
some distortion in the current when overexcited, although it
is generally of little consequence. There are, however, some
fractional horsepower, single phase motors that have a nearly
triangular waveform with significant third harmonic
currents .
Fig 10: specially connected Transformers

C. Series Reactors
This solution consists of connecting a series reactor with non
linear loads.

D. Tuned passive Filter

A filter may be installed for one load or a set of loads. The
filter rating must be coordinated with the reactive power
requirements of the load.

Fig 9: Transformer magnetizing current and harmonics

E. Active harmonic Filter

The active harmonic fillers are used to introduce current
component to cancel harmonic components of the non linear
VII. SOLUTIONS FOR MINIMISING HARMONIC loads. There are different types of active harmonic filters
CURRENT EFFECT such as Series filter, shunt filter and hybrid filter.

A. Over-sizing or derating of die installation The newest technology available for mitigation of
This solution does not eliminate harmonic currents flowing harmonics is the active filter. Active filtering techniques can
in the low voltage (less than 1KV AC) distribution system but be applied either as a standalone harmonic filter or by
masks the problem and avoid the consequences. The most incorporating the technology into the rectifier stage of a
widely implemented solution is over-sizing of the neutral drive, UPS or other power electronics equipment.
conductor. In existing installation, the solution is to derate
the electrical distribution equipment subjected to the Typically, active filters will monitor the load currents,
harmonic currents. filter out the fundamental frequency currents, analyze the
frequency and magnitude content of the remainder, and then
inject the appropriate equal and opposite currents to cancel
B. Specially connected Transformers the individual harmonics. Active filters will normally cancel
harmonics up to about 50th harmonic and can achieve
harmonic distortion levels as low as 5% THD-I or less. To
This solution eliminates third order harmonic currents. It apply active harmonic filters, determine the magnitude of
is a centralized solution for a set of single phase loads. harmonics (by measurement) that to be remove from the
system and select an active filter with suitable harmonic
current cancellation capacity.

ISSN: 2278 7798
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[4] J. Arrillaga, D. A. Bradley, and P. S. Bodger, Power

System Harmonics. New York: John Wiley & Sons, 1985, pp.

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[7] S. Bhattacharya and D. Divan, Synchronous frame based

Fig.11. Shunt Active Filter controller implementation for a hybrid series active filter
system, in IEEE/IAS Conf. Proc., 1995, pp. 25312540.
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passive solutions and may be similar to that for a variable IEEE/IAS Conf. Proc., 1976, pp. 529535.
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harmonic cancellation current, the prices of active filters can 0-471-90640-9.
range from about $30,000 (50 amps) to $100,000 (300
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[11] M.I.Abu BakarAssessments for the Impact of
Harmonic Current Distortion of Non Linear Load In Power
This paper present a survey of harmonics distortion in the System Harmonics, Transmission and Distribution
voltage and current waveforms with an objective to know the Conference and Exposition: Latin America, 2008 IEEE/PES,
existing level of harmonic distortion present in the Power 2008 , Page(s): 1 - 6.
System and future trends. Harmonics injected by some
commonly used nonlinear loads are studied. It is observed
that significant distortion in the current exists due to the use
of computers and other electronic equipments in residential Manish Kumar Soni was born in Rahod Nagar (Chhattisgarh), India, in 1988.
and commercial areas too. Increasing use of these He received the Bachelor Degree in Electrical Engineering from Chhattisgarh
equipments may result in serious problems in near future. Swami Vivekanand Technical University, Bhilai (C.G.) in 2010 and the Master
of Technology Scholar in Power System from Shri Ram Institute of
The current distortion differs widely from one section to the Technology, Jabalpur, RGPV University, Madhya Pradesh in Electrical
next. Although, voltage distortion is recorded below the Engineering. His research interests in Power system and Harmonics .
acceptable limit, but it is found above the recommended limit
Nisheet Soni has received his B.E degree in Electrical and Electronics from
at the places of high current distortion, as it depends on the R.G.P.V., Bhopal in 2005 and M Tech degree in Electronics and
circuit impedance as well as harmonic generation Communication from Indian Institute of Information Technology Design and
characteristics. Significant distortion in the current is Manufacturing (IIITDM, Jabalpur). He is currently working towards PH.D.
Degree at R.G.P.V., Bhopal. Currently He is Assistant Professor at Shri Ram
recorded at customer end with high percentage of 5th and 7th Institute of Technology, Jabalpur (M.P.). His Primary areas of interest are
harmonic components. Power systems, Power Electronics and Control techniques, Power quality


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