Reactive power management and voltage control of large Transmission System using SVC (Static VAR Compensator)
ABSTRACT The role of the transmission network in the Power System is to transmit the power generated in the power plants to the load centers and the interconnected power systems. The transmission of electric power has to take place in the most efficient way in addition to providing flexibility in the process. Flexible A.C. Transmission System (FACTS) promotes the use of static controllers to enhance the controllability and increase the power transfer capability. Providing reactive shunt compensation with shunt-connected capacitors and reactors is a well established technique to get a better voltage profile in a power system. Shunt capacitors are inexpensive but lack dynamic capabilities, thus some form of dynamically controlled reactive power compensation becomes essential. This feature is provided by Static VAR Compensator (SVC). The work presented here also compares SVC with fixed capacitor compensation and documents the superiority of SVC using Computer Simulation and its performance for reactive power management and better voltage control.
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ABSTRACT: The authors introduce special modifications to the basic Dommel algorithm to expedite simulation of systems including arbitrary configurations of individual power-electronic switching devices. The techniques have been implemented in a prototype transients simulation program. Two time-step sizes are used. Individual switching devices are represented according to simple characteristic curves. The modified algorithm includes iteration of a time-step when required to provide solutions on the curves. A technique is described for removing numerical oscillations of currents in capacitive loops and voltages at inductive nodes. Simulation results are presented for an example power electronic apparatusIEEE Transactions on Power Delivery 11/1991; · 1.52 Impact Factor
- IEEE Power Engineering Review 08/1988; 8(7):3-4.
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ABSTRACT: The recent availability of Electromagnetic Transient Programs with graphical front ends now makes it possible to put together models for circuits and systems in a manner similar to the connection of components in a laboratory, In the past, the nongraphical EMT Programs required considerable expertise in their use and thus distracted the students into the details of simulation. The introduction of a graphical simulation based laboratory into undergraduate and graduate power engineering education programs is presented, based on the PSCAD/EMTDC program. The philosophy behind the design of suitable example cases is presented within the framework of an Undergraduate Power Electronics Course, an HVDC Transmission Course and a course on Power System ProtectionIEEE Transactions on Power Systems 06/1996; · 2.92 Impact Factor
Reactive Power Management and Voltage Control of
large Transmission system using SVC
(Static VAR Compensator)
Pravin Chopade '. Dr. Marwan Bikdash,Dr.Ibraheem
ComputationalScience and Engineering
North Carolina A & T State University, Greensboro, USA
(I.Author is doingPh.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
techniqueto get a better
tatic VAR Compensator
comparesSVC with fixed capacitor
role of the transmission
the power generated
in the power plants
has to takeplace in the
to prQviding flexibility
Sy tern (FACTS)
to enhancethe controllability
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,staticVAR Compensator
thyristor, power converter.
building new lines. However, most high voltage transmission
systems are operating below their thermal
constraintsas stabilitylimits. EPR£ is pioneering flexible ac
transmissionsystem (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
Transmission System Program (FACTS).
of growing demandon
rating due to such
to make it possible
up to their thermal
Reactor (TCR) with
were available for
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
accuracy and validity of the results as compared to Fixed
CapacitorCompensation.The static VAR compensator is now
maturetechnology thatis widely
applications.Electric utility industry standardization of basic
models IS needed, and is recommended
dynamic stability improvement
using a power systemstabilizer
(reactive volt-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
transmission system inan advantageous,
which may normally be unacceptable from the point of view
mechanical control system,and y t it can respond with high
speed to deal with the stability/security
.Power electronics is
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 verifythe
used for transmission
in this paper . The
of a longitudinal power system
(PSS)and a static VAR
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
(SVS) as VAR
of SVS is to provide high
I. Voltage Control
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
powersystem . The basic
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
overload or contingencyconditions.
inexpensive but lack dynamic capabrlities, thus some form of
dynamically controlled reactive
determined by the real component
affected by the shunt compensation.
instead of a capacitor in shunt will reduce the voltage. Instead
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
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 inductancein 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 achievedin every cycle
Thyristor controlled Reactor (TCR)
TCR plus Fixed Capacitor (FC)
Thyristor switched Capacitor (TSC)
TSC plus TCR
depending on the
Voltage Regulator(AVR). So
of the voltagewaveformby
(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,
inductivecurrent is supplied.
operationwillbe 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 pointof steady 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 controlwere 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 operatingpoint.
3  the
droop is set characteristics
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. Generationof harmonics
phase angle control application. The SVC's are provided with a
voltage regulator whose gain and other parameters are selected
to meet the requiredperformance
"locations in the network the controlled
ensure a good voltage profile under
Whenthese devices can 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-
system, simple two-bus system connected
is used for simulation. The system data and line data is given in
Appendix.The system consists
generators. Sending end operated at 63 degrees and receiving
endgenerator operated at0
measuring and plotting icons are connected at various sections
of SVC: For simulating SVC in power
by transmission line
of two 230kV, 50 Hz
Above two bus system with fixed capacitor compensation
(blockdiagram) is shown in figure
PSCAD/EMTDCCN.I). The system
simulated in PSCAD/EMTDC CN.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
based on state variable techniques. A state variable formulative
solves the differentialequations
voltages and inductor currents.
400 is availablewhich is
of the systemfor capacitor
Figure 4: System with fix capacitor compensation
( Simulateddiagram is shown PSCAD IEMTDC CN I)
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 interfaceswith 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
circuitis shown in figure 5. It shows two sources
"sendingend" 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
performancewhen a SVC replaces
The voltage and power of the FC branch are also measured.
Another breaker (Rebrks) is used to connect the receiving end
source to 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
midpoint has 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 - ---
H(}--,,-.- -::- -
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 reactivepower
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
TCRand the numberof
(maximum 2) respectively.
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, cutting out 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-pointcompensation 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
voltageis 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).