Reactive Power Management and Voltage Control of
large Transmission system using SVC
(Static VAR Compensator)
Pravin Chopade '. Dr. Marwan Bikdash,Dr.Ibraheem
Computational Science and Engineering
North Carolina A & T State University, Greensboro, USA
(I.Author is doing Ph.D. at NCATSU, USA and Assc. Professor
of Electrical and Computer Engineering,
at Bharati VidyapeethDeemed University College of EngineeringPune.INDIA)
System is to transmit
efficient way in addition
Flexible A.C. Transmission
technique to get a better
capacitors are inexpensive
tatic VAR Compensator
compares SVC with fixed capacitor
performance for reactive
role of the transmission
the power generated
in the power plants
has to takeplace in the
Sy tern (FACTS)
to enhancethe controllability
capacitors and reactors
voltage profile in a power system. Shunt
but lack dynamic
(SVC). The work
in the process.
is a well established
the use of
(SVC), Power Electronics,
AC transmission,FACTS,static VAR Compensator
thyristor, power converter.
building new lines. However, most high voltage transmission
systems are operating below their thermal
constraints as stability limits. EPR£ is pioneering flexible ac
transmission system (FACTS) technology
to load lines at least for some contingencies
limits without compromisingsystem reliability.
Static VAR Compensatr (SVC) was first introduced
capacitor(TSC) or ThyristorControlled
fixed power factor correcting capacitor. Such SVCs were then
transmission system by using TCR in combination with TSCs.
Until the 1990s no suitable GTO devices
use in high power applications.
Institute (EPRl) has encouraged
devices in power transmission
TransmissionSystem Program (FACTS).
systems are becoming
of growing demandon
rating due to such
to make it possible
up to their thermal
Reactor (TCR) with
The Electric Power Research
the use of power electronic
system under its Flexible
deals with the simulation
with the associated details of the circuit design [I]. Further the
performanceevaluationhas been carried
accuracyand validityof the results as compared to Fixed
CapacitorCompensation.The static VAR compensator is now
applications.Electric utility industry standardization of basic
modelsIS needed, and is recommended
dynamic stability improvement
usinga power systemstabilizer
(reactivevolt-ampere) compensator (SVC) is reported. Results
SVC are very effectivein damping system oscillations
The recent availability of Electromagnetic Transient Programs
with graphical front ends now makes it possible to put together
modelsfor circuits and systems in a manner similar to the
connectionof componentsin a laboratory . High speed
transmissionsystem inan advantageous,
which may normally be unacceptable from the point of view
mechanicalcontrol system,and y t it can respond with high
speed to deal with the stability/security
semiconductordevicescalled thyristors, configured in many
accomplishac to deor dc to ac conversion,
conversion,switching,reactive power generators and many
capabilitychanges fromtens of kilowatts to thousands
of SVC on PSCADfEMTDC along
out to verify the
in this paper . The
of a longitudinal power system
(PSS)and a staticVAR
indicate that the PSS and the
steady state mode,
In transmission line compensation, the main objectives are
of voltage regulation and reactive
2.Improvement in system stability.
in achieving all these objectives.
must have abilityto respond
speed reactive power load compensation
stabilization and stability improvement. The specific functions
of an SVS can be summarized as follows
of SVS is to provide high
2.Prevention of Voltage collapse
3.Damping of Power Oscillations
and reactors is
compensation with shunt- connected capacitors
a well established technique to get a better voltage profile in a
compensation required, to compensate reactive
the fixed shuntcapacitors being well distributed
network and located preferably closed to the loads. This would
ensure reasonable voltage profile during steady state condition.
However, this may not be adequateto
inexpensive but lack dynamic capabrlities, thus some form of
dynamically controlled reactive
.essential. The phase angle
determined by the real component
affected by the shunt compensation.
instead of a capacitor in shunt will reduce the voltage. Instead
of mechanicalswitching (using
devices, we can use thyristor
control capability radically. This approach is called static VAR
power loads, is
of the line current, is not
Similarly, adding a reactor
The basic reactive components
shunt reactors and shunt capacitors. These reactors are varied
by means of thyristors. The capacitor banks are either a fixed
amount or are varied in steps by thyristor switching. Based on
theseprinciples various static
developed. These are characterized by fast response, reliability,
low operatingcosts and flexibility.
of a static compensator are
Basic Description of Static VAR Compensation(SVC) [I]
SVC can be of one of the following types:
Figure 1 is a one-line diagram of a typical
system for the transmission application. TSC plus TCR is very
popular and most effective. Figure I gives the general idea of
realization of SVC using TSC plus TCR scheme. The idea is to
sense the voltage of the line and keep it stable by introducing
capacitanceor inductance in the circuit,
signal generated by Automatic
obviously, the gating signals to thyristor valves will have to be
changed in accordance with the AVR signal. Since control can
be achieved in every cycle
Thyristor controlled Reactor (TCR)
TCR plus Fixed Capacitor (FC)
Thyristor switched Capacitor (TSC)
TSC plus TCR
Voltage Regulator(AVR). So
of the voltage waveformby
(controlling the conduction timeolr
very fast and accurate. Compensator
figure 2. It shows that if the voltage decreases than the desired,
capacitive current is supplied and when the voltage over shoots,
operationwill be at theintersection
characteristics and the system
disturbance in power system (e.g. throwing off of a load from
the system), the load line has shifted from B I to B2 (refer to
figure 2 ).
thyristors), the control is
characteristics as shown in
The pointofsteady state
due to a
load line suppose,
'- -- - -- - _ .. - - - _. --- - _. - --- - - - - _ ... - - - ------ -'
Figure I: Typicalstatic VAR system (SVS)
Before disturbance, the steady state point was at "a". If the
response of the TCR control were slow, the operating point
would have moved straight to point "b", but since the thyristor
control is very fast, the voltage,
point "b", will stabilize at point "c". This describes the typical
control action of a SVc.
even before overshooting to
a·, 1 .
angle '. ...../ ~
, '. i .-
Figure 2: Effect ofTCRCompensationon operating point.
3  the
droop is setcharacteristics
depending on the SVC rating and the short circuit level of the
controlledbus. Under normal
control should be set to zero MV AR exchange with the system.
During distributed conditions the SVC susceptance is varied by
the regulator to counteract the voltage oscillations.
network conditionsthe SVC
Figure 3: Typical SVCCharacteristics.
Reactive Power Compensation
for the former and Thyristor controlled
latter function. TSC's bring about harmonic free step control of
reactive power while the TCR's enable continuous control of
reactive power. Generation of harmonics
phase angle control application. The SVC's are provided with a
voltage regulator whose gain and other parameters are selected
to meet the required performance
"locations in the network the controlled
ensure a good voltage profile under
Whenthese devicescan perform
response they serve to enhance the transient stability and could
help to prevent voltage collapse. The well-established
judiciously applied, becomes an attractive tool for transmission
by SVC: SVC's can supply
reactor (TCR) for the
reactive powerthe design.
(TSC) are employed
is inherent to any
when SVC's placed at key'
reactive power £ources-
when and newdevelopment
system, simple two-bus system connected
is used for simulation. The system data and line data is given in
generators. Sending end operated at 63 degrees and receiving
measuring and plotting icons are connected at various sections
of SVC: For simulating SVC in power
by transmission line
oftwo 230kV, 50 Hz
degrees power angle. The
and scaled for smooth
Above two bus system with fixed capacitor compensation
(block diagram) is shown in figure
PSCAD/EMTDC CN.I). The system
transmission line is shown
simulated in PSCAD/EMTDCCN.2.
with SVC connected to
diagram) in figure 5
CN.2).The SVC is
This SVC 400 model [4, 5] consists of a general static VAR
Compensator(SVC) model SVC
based on state variable techniques. A state variable formulative
solves the differentialequations
voltages and inductor currents.
400 is available which is
of the system for capacitor
Figure 4: System with fix capacitor compensation
( Simulateddiagram is shown PSCAD IEMTDC CN I)
- C.•.. ----...,
OQ~. (t viol
Figure 5: SVC 400 Model rco, .
Figure 6: System with SVC Compensation
(Simulated diagram is shown PSCAD IEMTDC CN2, CN3)
time-step is directly proportional,
elements to be modeled adequately. The SVC 400 compensator
model interfaces with EMTDC
source Figure5 shows the SVC 400 model
Simulation with PSCAD)
of the system matrices on the value of the
and thus the time-step can be
during run as it is required for the switching
program as a Norton current
(ICON use in
A practical system
sourcesconnected through a transmission
placed at the midpoint of the line as is usually the case. . The
circuit is shown in figure 5. It shows two sources
"sending end" and "receiving end" connected through
- =~5.0-Hz:_transmis&ioll-'ines :;Ii-ne.l" and :'li6t&"._Tlle data.for the -r;
transmission line .rnodel is given.. in, Appendix and consists- of
physical dimensions of towers
voltage, active power and reactive power are-measuredat
ends. Between the two transmission
at the middle of a long transmission line, fixed shunt capacitors
of 120 MVAR rating are connected
performance when a SVC replaces
The voltage and power of the FC branch are also measured.
Another breaker (Rebrks) is used to connect the receiving end
sourceto transmissionline. This breaker is opened
seconds during the simulation to create a disturbance. This will
bethe same as "throughoff'
Obviously,the voltage at the mid-point
Toreduce this voltage,capacitive
midpointhas to decrease. Here,
increase in the voltage, the FC will draw more reactive power.
So, the only way to pull down the voltage is to switch off the
capacitors.This is achieved by switching off MPBrks
seconds. Here, 3 milliseconds time is considered for sending,
relaying and breaker operation (this can be the worst case).
is simulated[4J cornpnsmg
line and the SVC
and -conductors" 'along. with
both - ---
line models i.e. practically-
in delta through
is analyzed to compare
the Fixed Capacitors
is bound to shoot up.
on the contrary,
Circuit used for Simulation: PSCADIEMTDC
used for simulation. It has a model for SVC comprising ofTCR
and TSC. Following consideration
model [PSCADIEMTDC CN-2]
are made while using this
A suitable voltage measurement
to reduce ac harmonics and de ripples to obtain
measurement for the controller.
technique is necessary
2.A droop of the measured voltage should be derived to
obtain a specific SVC regulation
shown in figure 3.
requirement into on/off signal for the TSC and a reactive
power demand for the TCR.
should be used to split a reactive power
Control and Firing Circuit for SVC: Now the same circuit
is provided with SVC instead of Fe. This is shown
removed now as it is not required. The SVC is connected
system through a 200 MVA 230/11
comprises of a 100 MV TCR in parallel with a 167 MVAR
capacitor bank which is divided in two equal stages.
circuit ofSVC is shown in figure PSCADIEMTDC
KV transformer. The SVC
simulation results with FC compensation
We can observe from (d), as soon as the load is thrown off (at
are shown in figure 7.
1.8 seconds), the voltage shoots up to around 1.5 pu from I pu.e?
After the FC are cut off, the voltage comes down to around 1.1.
pu which is still higher than the required I pu. From (c), we
observe that the capacitive power drawn by the FC rises with
the voltage. The real power remains
capacitors are considered ideal. From (a), we can observe the
reactive power at the sending and the receiving end, whereas
(b) shows the real powers. Thus, we can increase the maximum
power transfer capability of line with FC, but the voltage
control is not satisfactory.
zero throughout as the
M -:[\'-,....~·-·---'-----.I------ ...•• Cr-
'--n_ ..•••.~ .. ~.... _.
•Re:'1.1 po •••. "er at-s-e. -
R.\fS undpourt voltage
Figure 7: Performanceof the system with Fix Capacitor Compensation
(a, b, c & d)
goes from II0 MYAR leading to 35 MVAR lagging
figure 8(c» to effectively
cycles and make it perfectly
(refer figure 8(e)). Figure
TCR andthe number of
state, both the capacitor stages are switched on (167 MVAR
leading)but as seen before a leading reactive power
MV AR only is required to maintain the steady state voltage
profile. So, the 'I'Ckconducts with a firing angle of about 130°
to ensure this. After the disturbance, _the voltage is controlle
-by, cuttingout both,-capacitor=stages
angle to about 1-25°.-
the reactive power supplied by SVC
control the over voltage within 2
stable in about. 15 milliseconds
8(d) shows the firing angle
To maintain voltage during steady
and adjusting the firing-7 __ -
-,...: -'. '_'::..----
The Simulation resu-r?s of the power profile with SVC are
shown in figure 8 (a) to figure 8 (e). The same power profile as
with FC is achieved by SVC also. It maintains the same steady
state voltage of 1 pu (refer figure 8 (e) and provides the same
mid-point compensation of 110 MVAR leading in steady state
as Fe. The reactive power at sending end and receiving end are
also same (refer figures 7(a), 7(b), 8(a), 8(b», but SVC draws
real power of 10 MVAR from the system to compensate
internal losses (refer figure 8(c»
and SVC. The vastly superior capability ofSVC to control over
voltage is clearly established.
seems to be that the voltage transiently shoots up to about 1.71
pu. whereas it rises to a maximum of about 1.6pu with Fe.
Figure 9 shows co mpaTISon'between performances-with
The only drawback with SVC
• Reactive power at s.~.
::,;:.~.--."--"~-----.--'-'-:' -... '-'..~-' ..-"--~«((v:~:: -.. ,
. 6~, .:---.----- ..----~-,.--m.,:-'-"--!V-'.----'--.-
·!OO L-~ ~ __~~_
• Real power at r. I!.
-+---: -,_- .. -.=--~-- .. ~--., .. -l,A·
. 'J'~~:..-- ~~.:•
ruin~ angle ( croerec)
by S~C) -:::--~ • -.~-----:.-.: - -.
Figure 8: Performance of the system with SVC (a, b, c, d & e)
• Vol. with capecuor• \"')1. with SVC
Figure 9: Comparison
of voltage control capabilities of Fixed
(FC) and Static V AR Compensator (SVC).
V. Download full-text
proved. In addition
about SVC. SVC has much superior voltage control capabilities
both, in steady and transient
switched shunt capacitor and reactor compensation.
it is found that SVC can effectively use to
and reactive powercompensation.
SVC over fixed capacitor
to this we have following
state than theconventional
I.Due to above, SVC improves
the transientstability of
profile of SVC in case
presence of TSCs tends to increase the
of a fixed
capacitorin the circuit
in voltage control
of SVC is satisfactory in case the system
selected while running the SVC case.
Simulationon PSCAD- following data
control slider at K.B.Vrer slider :lpu,Mid-point
switch kept closed. At the sending end voltage of the
source:230KV and phase angle of source:
At receiving end voltage of the source: 230 KV, phase
angle of the source: 0 degree.
Controller Sli crs:Kp:4.0,Tl :0.0 t,
Professor, Electrical Engineering
while carrying out study on simulation of SVC with PSCAD at
Indian Institute of Technology (LI.T.), Powai, Mumbai,INDIA.
TheAuthorsof this paper
Management of Bharati Vidyapeeth
Deemed UniversityPune, Dr. Anand R. Bhalerao, Principal
and Dean, Bharati Vidyapeeth
gratefully acknowledgeDr. S. A. Khaparde,
Department, Indian Institute
Mumbai,INDIA(U.T.), Powai,for his help
Pune, Bharati Vidyapeeth
Deemed University College of
INDIA,for their supportand constant
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G., "Applicationof Static VAR
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