HARMONICS IN POWER SYSTEM AND ITS MITIGATION
TECHNIQUES
A.J. Mehta K.L. Mokariya
Professor, Electrical Engg, G H Patel College of P.G. Student. Department of Electrical
Engg&Tech Vallabh Vidhyanagar. Engineering, ISTAR, V.V.Nagar, India
draxaymehta@gmail Kashyapmokariya2000@yahoo.com
ABSTRACT
In this paper, various harmonic sources, their effects on power system and its mitigation techniques is
presented comprehensively. Firstly the The measurement of harmonics by Digital storage Oscilloscope
(DSO) is briefly discussed and than the various techniques of Passive filter and Active filter are
discussed. Further the Mat lab simulations for passive and active filters are presented..
Keywords: Harmonics, Nonlinear load, Active and Passive Filtering and Tuning of controller
1. INTRODUCTION Measurement of Harmonics
The Ac power system harmonic problems are The harmonics can be measured by Harmonic
mainly due to the substantial increase of non-linear Analyzer or digital storage oscilloscope.Figure2
loads. Due to technological advances, such as the shows the reading taken on the Arc furnace of
use of power electronics circuits and devices, in 350KW rating by the load manager ALM10
Ac/Dc transmission links, or loads in the control of cryward.The 11th harmonic was found dominant in
power systems using power electronic or Arc furnace.
microprocessor controllers. Such equipment
creates harmonics throughout the system. In Furnace Rating
general, sources of harmonics are divided into: (a) Furnace Rating:-350 kw
Domestic loads (b) Industrial loads (c) Control V=463.7 volt
devices. The detailed classification is shown in I=346 Amp
Figure1. Leakage current=5.7 Amp
O/P voltage=1600 volt
O/P Frequency=850 Hz
Figure 2 Measurement of Harmonics
V THD= 106.7 %(Fundamental)
= 35.4% (3rd)
= 26.4 %(5th)
Figure .1 = 33.3 %(7th)
A compensator is essential in order to minimize =41.9 %(9th)
the effects of the non-sinusoidal waveforms in the =49.1 %(11th)
distribution system. A proper compensator can
only be designed if the definitions of all the
components of electric power under non-
sinusoidal waveforms are accurate and have an
interpretation in terms of the connected load.
that synchronizes to the zero-crossings should be
considered vulnerable to disruption by harmonic
distortion.Fractional and sub-harmonics can affect
video displays or televis ions. Fractional
harmonics are frequencies that are not integer
multiples of the fundamental frequency. Sub
harmonics are frequencies below the fundamental
frequency. Fractional harmonics produce an
amplitude modulation of the fundamental
frequency.
Effect on Transformers: The primary effect of
power system harmonics on transformers is the
additional heat generated by the losses caused by
the harmonic contents generated by the load
current. Other problems include possible
Figure3 Measurement of harmonics by DSO resonance between the transformer inductance and
the system capacitance, mechanical insulation
harmonics of UPS (on load) stresses due to temperature cycling and possible
small core vibrations. The primary loss
120 components are the winding I2R losses and
winding eddy-current losses. The losses due to the
% of fu nd am en tal
100
80 I2R component are due to conductor heating and
60 %Fund
the skin effect. It is found that, losses from the
40
winding eddy-current increase with the square of
20
the frequency.
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 2. TECHNIQUE OF HARMONIC EFFECT
harmonic number MINIMIZATION
(A) Passive Filtering
(B) Active Filtering
Figure 4 Measurement of harmonics by DSO
2. HARMONIC EFFECTS ON DEVICES AND
LOADS
Insulation stress (voltage effect): Insulation stress
depends on the instantaneous voltages, as well as
its firing rate.
Thermal stress (current effect): Thermal stress
depends on the presence of harmonic currents. .Figure 5 Different types of Active Filter.
Harmonic currents can cause copper losses, iron
losses and dielectric losses in the equipment.
Passive Filtering
Load rupture (abnormal operation): Several A shunt filter is required to trap the harmonic
electronic devices are subject to this contingency, current to correct the power factor of the load and
because their normal operation depends on the properly filter the harmonics of the load. Figure 6
existence of a purely sinusoidal voltage source. shows a simple example of a single frequency
Specifically, harmonic currents circulating in tuned filter for fifth harmonic. Figure 7&8 shows
electric machine armatures can generate pulsating supply current waveform with and without passive
electromagnetic torques.A vivid example is a filter. Figure 9&10 shows Plots of band pass and
household digital clock that will rapidly advance band stop filters. Traditional passive filtering
the time in the presence of additional zero- approach is no longer attractive due to several
crossings from harmonic distortion. Any device shortcomings. The filter components are very
bulky because the harmonics that need to be
suppressed are usually low order. Passive filter are
known to cause resonance and hence affecting the
stability of power system. It will not work
effectively for varying load conditions. Design of
Passive Filter is as shown under.
Design of Passive Filter
Q=Reactive Power Consumed in VA
Vs=Supply Voltage in Volts
f=Supply Frequency in Hz
n=Harmonic Order
QL=Quality Factor
XC= (Vs^2) (n^2)/Q (n^2-1)
XL=Xc/(n^2)
L=XL/(2*3.14*f) Figure 8 supply current waveform with passive
R=(n*XL)/QL filter.
R=0.033 ohm
L=28.7 mh
C=14.2 microfarad
Rs=1.2 ohm
Ls=2.2 mh
CL=100 micro farad
RL=20 ohm
Vf=0.8 volt
Figure 9 Band Pass Passive Filter.
Figure.6 Single frequency tuned filter for 5th
harmonic.
Figure 10 Band Stop passive Filter.
Active filtering
An active power filter compensates for harmonics
and corrects the power factor by supplying the
harmonic currents drawn by non-linear loads.
Generally, the active filter is connected in parallel
Figure 7 supply current waveform without passive with the harmonic-inducing load. The APF is
filter. standard voltage source inverter having an energy
storage capacitor on the dc side. The PWM (Pulse
width modulation) is employed to generate gating
pulse to the switches of the Active Filter. The dc
based load fed from the bridge with a capacitor is
nonlinear load on AC mains Circuit diagram
showing this scheme is given in Figure 11. In this
active filter subtraction of fundamental from the
total current by means of notch filter will give the
harmonic current. Here PI control Technique is
used for providing control signal. Sensed dc
voltage of the APF is compared with its set
reference value in the error detector, voltage error
is processed in the proportional-Integral (PI)
controller according to that gating pulse are
generated with pulse width modulation technique.
Tuning of PI controller is obtained for KP=0.1 and
KI=0.8. The fast switching IBGT in APF
application causes switching frequency noise to
appear which requires additional filtering. Design
Parameters for active filter are shown as under.
Design Parameters of Active Filter Figure.13 Voltage waveform with filter.
R1=0.25 ohm
L1=2.5mh 4. CONCLUSIONS
RG=1ohm In this paper with Passive filter the total harmonic
LG=2.5mh distortion in current is 2.46% and with active filter
RL=20ohm total harmonic distortion is 1.06% which is less
CL=100micro farad than 5% as per IEEE519.
KP=0.1
KI=0.8 5. REFRENCES
Cf1=11000 microfarad
1 Zainal Salam, Tan perang and Awang Jusoh
“Harmonics Mitigatation Using Active Filter a
Technological Review “vol8,no2,2006,17-26.
2 IEEE Recommended Practise for monitoring
electric power quality approved june14,1995.
3 A Mansoor,W M Grady,A.H Choudhary,M.J
Samotyi,1995.”An Investigtion of Harmonics
attenuation and diversity among distrubted single
phase power electronics loads”,IEEE Transctions
on power delivery vol10,1,1995.
4 W.M Grady and S Santaso,”Understanding
power system Harmonics.” IEEE power Engg
Review,vol 21,no11,pp 8-11,2001.
5 J.C Das “Passive filter Potentialities and
Figure 11 Active Harmonic Filter. limitation.” IEEE Trans on Industry
applications,vol 40,n0 1,2004.
6 Power system harmonics by J
Arrilaga,Newyork,Wiley 1985.
7 “Steady state performance of a controlled
current active filter” Richard M Duke Published
in IEEE Transcations on power Electronics vol
8,no 3 1993.
8” Active power filter for non linear AC
loads”Janko Nastran IEEE Transcations on power
electronics vol9,no1,1994.
Figure.12 Current waveform with filter.
