International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 6, June 2014)
Investigation of Effect of Harmonics on Voltage Stability in a
Grid System by SVC
Gaurav Shrivastava1, Prof. S. K.Tripathi2, Prof. Sunil kumar Goel3
1
M.Tech Student, Power Electronics & Drives, K.I.E.T, Ghaziabad, India
Associate Professor, Electrical & Electronics Engineering, K.I.E.T, Ghaziabad, India
3
Professor, Electrical Engineering, Meerut Institute of Engineering &Technology, Meerut, India
2
*It improves the load power factor nearly unity so that
current drawn from the source will be in phase with the
system voltage.
*Suppression of harmonics in load so that current drawn
should be sinusoidal,
*Voltage regulation for the loads that cause fluctuations in
the supply voltage.
*Cancelation of the effect of unbalance loads so that
the current drawn from the source should be balanced
(load balancing).
Abstract— This paper investigates the role of Static
Var Compensator (SVC) on stability of voltage in grid
system due to the presence of harmonics.. Here the design of
SVC is based on the combination of Thyristor switched
capacitors (TSC’s) and Thyristor controlled reactor (TCR) .
TSC’s are used for switching the capacitor banks on and off
while the TCR continuously controls the reactive power by
varying the current amplitude
flowing through the
reactor.But harmonics are induced in grid system due to
TCR.In this paper FACTS controller such as Static Var
Compensator is used to maintain the system voltage within
limit by minimizing the harmonics internally. It is proposed to
develop SVC with firing angle controller for 220KV,100 MVA
transmission system. Proposed work is aimed at mathematical
modeling of svc,development of control strategy and
investigations of the performance of control strategy using
MATLAB/SIMULINK.
II. STATIC VAR COMPENSATOR
Static var compensators, regarded as the first FACTS
controllers, have been used in North American
transmission systems since late 1977 in western Nebraska
[6].
According to definition of IEEE PES Task Force of
FACTS Working Group: [3]
Static Var Compensator: A shunt connected static var
generator or absorber whose output is adjusted to exchange
capacitive or inductive current so as to maintain or control
specific parameters of the electrical power system
(typically bus voltage).
In general, an SVC is a combination of ThyristorControlled
Reactor(TCR),
and
Thyristor-Switched
Capacitor (TSC) .
Keywords— {Flexible a.c.transmission system (FACTS),
Static
var
compensator(svc),
Thyristor
controlled
reactor(TCR), Thyristor switched capacitor(TSC), Power
electronics, Thyristors etc}.
I. INTRODUCTION
Now a days,the power systems are very unsecure due to
the voltage instability problems because of large
transmission networks having many generating stations,
buses and different types of load patterns and deregulaton
of the electricity industries.Due to the lack of reactive
power support,the power system is becoming more
vulnerable and leads to voltage collapse.So reactive power
compensation is very much essential to maintain the system
voltage within limit.This task is accomplished by FACTS
Controllers[1] that improves the overall performance of the
power system.
Shunt Facts controllers such as Static Var
Compensator(SVC) controls the system voltage effectively
by adjusting the reactive power output at the connection
point[3].
The primary objectives of a shunt compensator in the
grid system are as follows :-
A- BASIC DESCRIPTION OF TCR AND TSC
The term, “SVC” has been used for shunt connected
compensators, which are based on thyristors without
gate turn-off capability[1]. The SVC consists of a
coupling transformer,a Thyristor controlled reactor and
Thyristor switched capacitor.TCR continuously controls
the reactive power by by adjusting the amplitude of current
flowing in the reactor while TSC is used to automatically
on/off the capacitor banks.In transmission networks for
regulating grid voltage SVC is used. When the power
system's reactive load is capacitive (leading), the TCR
activates and absorbs reactive power thus lowers the
system voltage.
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 6, June 2014)
When the load is inductive (lagging), the TSC activates
and automatically switch on the capacitor banks to provide
reactive power to make system voltage high[1]. Thus in
both the conditions the system voltage remains with in
limit.
Figure-2, shows the distribution unit that determines the
firing angle alpha for TCR by using primary susceptance
Bsvc which is computed by voltage regulator.The firing
angle α as a function of TCR susceptance
can be
implemented by a look-up table by the equation,
III. CONTROL SCHEME
……….(1)
=
The control system having different units is described as
follows,
Where
is the TCR susceptance in pu of rated TCR
reactive power .
(a). Measurement system- The positive sequence voltage
which is to be controlled is measured by measuring unit.A
fourier based measurement system that uses a one-cycle
running average is used.
(b). Voltage regulator - It is the main unit of SVC
controller.This unit determines SVC susceptance B in order
to keep system voltage constant.To determine the
susceptance B ,the voltage regulator uses voltage error
which is the difference between the measured voltage
(Vmeas.) and reference voltage (Vref.).
(c). Distribution unit- The firing angle alpha for TCR is
computed by this unit and it also determines number of
TSC‟s that switches the capacitor banks on and off
automatically.
(d).Synchronizing unit- This unit has a Phase locked
loop which is synchronized at the secondary voltage level
and pulses to the thyristors is sent by pulse generator.
TABLE- I
The parameters taken for simulation are as follows:Parameter
Value
TCR branch Inductance
18.7 mH
TSC branch Capacitance
308.4μF
TSC branch Inductance
1.13mH
Hysterisis- distribution unit
0.1 (pu/100MVA)
Transformer nominal power
2000MVA,50HZ
Transformer total leakage
0.15 (PU/Pnom.)
Nominal secondary voltage
11KV(rms,ph-ph)
Kp
60
Ki
1400
A- FIRING UNIT
There are three independent subsystems in this unit and
for each phase(AB,BC,CA) ,one subsystem is used.In each
subsystem,there is a pulse generator for each of the TCR
and TSC branch. Each subsystem having a phase locked
loop which is synchronized on line-to-line secondary
voltage .. The pulse generator generate pulses by using the
firing angle α and the TSC‟s on/off status coming from the
Distribution Unit. The firing of TSC branches can be
synchronized or continuous that is at every cycle one pulse
is sent to each positive and negative thyristor.The reduction
of harmonics is faster in synchronized firing mode. In the
Firing Unit dialog box,we have to select synchronized
firing mode..
Fig-1.Voltage regulator
Fig- 2. Distribution Unit
117
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 6, June 2014)
Fig -5. Measurements across SVC ,TSC’s and Load
V. SIMULATION RESULTS
Case- A:THD of Grid voltage when no harmonic is induced
This figure shows the T.H.D analysis of grid voltage
when no harmonic is induced in the system.From this
analysis we conclude that SVC controller is working
properly and it maintains the system voltage within limit.
Fig- 3.Firing Unit
IV. TEST SYSTEM MODEL
In this paper a 300-Mvar Static Var Compensator
system is designed that regulate voltage on a 100-MVA,
220-kV system of frequency 50 hz.. The SVC consists of a
220kV/11kV, coupling transformer, of 333-MVA,one
Thyristor-controlled Reactor bank and three Thyristorswitched Capacitor banks
that are connected on the
secondary side of the transformer.The main advantage of
SVC system connected on transformer‟s secondary is that it
reduces the size and number of components required in the
SVC system. The simulink model of the test system is
shown in figure 4.For the simulation purpose the SVC is
kept in the voltage control mode and its reference voltage is
set to Vref =1.025 p.u..First of all in Case -1,when no
harmonic is induced in the system then analysis is done in
Case-2,when 3rd harmonic is induced and Case-3,when 5th
harmonic is induced.The simulation results show the effect
of harmonics injection by TCR on system voltage.
Fig- 6. THD of grid voltage
rd
Case-B: When 3 harmonic is induced
This figure shows the waveforms when 3rd harmonic is
induced in the system due to TCR.The waveforms clearly
shows that there is no much effect of harmonic injection on
the secondary voltage.It shows that the Svc controller is
working properly and maintains the system voltage within
limit.
Fig -4.Simulink model of Test System
118
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 6, June 2014)
Fig -7. Waveforms of SVC when 3rd harmonic is induced
Fig-10. Waveforms of SVC when 5th harmonic is induced
Fig-11. THD of grid voltage at 5th harmonics
rd
Fig -8. THD of grid voltage at 3 harmonic
Fig -12. THD of secondary voltage at 5th harmonic
rd
Fig -9. THD of secondary voltage at 3 harmonic
The T.H.D analysis and waveforms shows that
secondary voltage is sinusoidal in nature and there is no
much effect of harmonics on secondary voltage.
The T.H.D waveforms shows that SVC Controller is
working logically in a proper manner.
Case-C: Waveforms when 5th harmonic is induced
This figure shows the effect of 5th harmonic injection in
the system due to TCR.The waveforms shows that there is
no much effect of harmonic injection on the secondary
voltage.
VI. CONCLUSION
The simulation results above,shows that the Static Var
Compensator can improve voltage profile in grid system
effectively.
119
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 6, June 2014)
The secondary voltage is sinusoidal in nature so it
proves that the svc controller is working well in all the
disturbing conditions.The current across load is in phase
with load voltage that makes it closer to unity power factor.
So it greately improves the quality of electrical power in
grid system. Also, this system has continuous control and
regulation from inductive to capacitive, and the response
time is faster.
BIOGRAPHIES
Gaurav Srivastava: Pursuing M.Tech in
“Power Electronics & Drives” from Krishna
Institute of Engineering &Technology,
Ghaziabzd. His area of interest is Power
electronics, FACTS and Control system.
(„gauravsri005@gmail.com‟)
REFERENCES
[1]
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Prof. S. K. Tripathi: Working as an
Associate Professor in the Department of
Electrical and Electronics Engineering,
Krishna Institute of Engineering and
Technology, Ghaziabad.His area of interest
is power electronics and drives.
(„surendra.27n@gmail.com‟)
Prof. S. K. Goel: Working as a Professor
in Electrical Engineering, Meerut Institute
of Engineering & Technology, Meerut
since 1999.He has more than 25 years of
experience in Industry and Teaching. He
has worked in several industries, in both public and private
sector. His area of interest include Electrical machines,
Power system, FACTS.
.(skgoel_miet@rediffmail.com).
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