The Comparative Analysis on FACTS Devices
of SVC, STATCOM and SSSC
Poonam pandey *
Siraparapu Satyanarayana
M.Tech (Power System),
Electrical Engineering
ITM University Raipur
Naya Raipur, Chhattisgarh, India
poonam0007pandey@gmail.com
Assistant Professor,
Electrical Engineering
ITM University Raipur
Naya Raipur, Chhattisgarh, India
satyanarayanas@itmuniversity.org
Abstract—The present power system network is very complex and it is difficult to maintain the power
system stability. The modern FACTS appliances are based on the conception of the VSC (voltage source
converter) to interpose a controllable AC waveform at fundamental frequency into the system to change
the power flow at buses or transmission line. FACTS devices are used to solve the various power system
steady stat problems. This paper gives competitive analysis of the three FACTS devices, which are: the
static var compensator (SVC), the static synchronous compensator (STATCOM), the static synchronous
series compensator (SSSC).the voltage destruction occurs when a system is loaded over its maximum
loaded capacity. It also gives the application of the SVC, STATCOM and SSSC.
Keywords— reactive power, power flow control, loads flow.
Abbreviations/acronyms-FACTS (Flexible alternative current transmission system), GTO (Gate turnoff
(thyristor)), SSSC (Static synchronous series compensator) STATCOM (Static synchronous
compensator), SVC (Static var compensator) TCR (Thyristor controlled reactor), TSC (Thyristor switched
capacitor), VSC (voltage source convertor).
1 INTRODUCTION
T
he power systems components are mainly
comprise generators, transmission lines,
transformer, passive and active compensators,
switches and loads. The networks of power
system are very complex that are nonstationary, nonlinear, and open to disturbances
and faults. Now in the year, the electrical
power system continually expanding in size
and increasing complexity all over the world.
The industry of electricity has undergone some
changes due to privatization of all over world
which
has
affected
power
system
management and energy markets[1]. The
power system which are heavily loaded,
faulted and having shortage of reactive power
are the most important reasons for voltage fall.
The voltage fall problem is related to reactive
power planning and also including the
contingency analysis, as these should be
considered for the secure and efficient
operation of the power system. Under the
outage condition of few critical lines, the
generators are able of supplying limited
amount of reactive power even sometimes the
reactive power, which is supplied, cannot be
used to achieve the requirement of the power
system network because the location is far
away from the generator point. Further, the
real or active power of the generators is
decreases to supply the reactive power
requirement of the system. That is why, the
reactive power compensators are used to
* Corresponding Author
maintain the voltage profile and thereby improving
the performances of the system [2]. The process
of power generation and transmission is complex.
To maximize the output of the power system we
requiring the working of so many component. The
reactive power of the system is one of the
important components.
The voltage disruption studies are importance
for the operation and design of power system. The
voltage stability is a most important consideration,
when the size and location of new var origin need
to be determined during the time of var planning.
Many methodologies have been proposed and
used for the study of the problem.
Flexible AC transmission system is an
evolving technology to help electric utilities [3], [4].
To improve the quality of supply in the networks of
electrical power systems through the applications
of
development
in
semiconductor
power
instruments that means utilization of static power
converters in networks of electrical energy. The
technological advances that react more like an
idea switch totally controllable, admitting high
frequencies on commutation to major levels of
tension and power [4].
For improving the overall performance of the
power system, Flexible Alternating Current
Transmission System (FACTS) devices are being
very popular. These devices are the solid stat
converters. They have capability of improving
voltage profile, transmission capacity, security and
enhancing power system stability. In modern days
the fact controllers are use in power system,
which is recent development of power
electronics. FACTS controllers are able to
controlling the network condition with very fast
response and this feature of FACTS can be
absorbed to increase the voltage stability, and
transient stabilities and steady stat stabilities of
a complex power system. It increased
utilization of existing electrical network closer
to its thermal loading capability, and avoiding
the need to construct new transmission lines.
The realization of power electronic based
FACTS controllers has two generation they
are:

First
generation
have
thyristor
switched reactor and capacitor and
quadrature tap changing transformer.

Second generation have GTO (gate
turn -off), VSC (voltage source
convertor).
By use of FACT controller’s line,
impedance and one can control the variable
such as phase angle and voltage at chosen
bus. There are five popular FACTS devices
utilized by the requirement of this purpose.
This FACTS devices are (SVC) static var
compensator, (STATCOM) static synchronous
compensator, (TCS) thyristor controlled series
capacitor, (SSSC) static synchronous series
compensator and (UPFC) unified power flow
controller .they have their own characteristics
and limitations. Static var compensator
st
controller is a 1 generation facts device. svc
control voltage at a required bus thus
improving the voltage profile of the system.
The svc’s primary task is to maintain the
voltage at a defined bus by means of reactive
power compensation. SVCs have been used
for high performance steady state and
transient voltage control compared with
classical shunt compensation SVCs are also
used to dampen power swing, improve
transient stability, and reduce system losses
by optimized reactive power [5],[6].
continuous voltage by a condenser and for the
compensate the losses of VSC. The SSSC is able
to exchange reactive and active power with the
transmission system.
2 SVC (STATIC VAR COMPENSETOR)
SVCs are the set of electrical device. It is first
generation facts controller. It is used for producing
fast acting reactive power at high voltage electrical
transmission networks. It is an automatic
impedance matching device, where the back to
back connected, SVCs is connected in parallel
with the transmission line. SVC act as a generator
or as a load, the output of this is adjusted to
exchange inductive or capacitive current to control
or maintain specific power system variables. SVC
systems are applied by utilities in transmission
application for some purposes. The first purpose is
for rapid control of voltage at weak point of
network. Installation may be at the line ends or at
the midpoint of transmission interconnections.
SVC is just like asynchronous condenser but it has
no rotating part, is used To supply or absorb
reactive power. in Fig. 1 the basic structure is
shown. The svc is connected to the coupling
transformer that is connected directly to the ac bus
whose voltage is to be regulated .from Fig.1; SVC
is composed of controllable shunt reactor and
shunt capacitor. Total susceptance of SVC can be
controlled by controlling the firing angle of
thyristors. However, the SVC acts as like fixed
inductor or fixed capacitor at the minimum and
maximum limit [7,8]. This is designed to bring the
system closer or ideally equal to the unity power
factor. SVC devices are used in two main places.

For regulating the transmission voltage, it
is connected to the power system
(transmission SVC)

To improve power quality, it is connected
near large industrial loads (industrial
SVC).
Shunt
compensation
device
is
STATCOM, from the family of FACTS. It is a
solid stat voltage source convertor and it is tied
to a transmission line. A STATCOM injects
current that is almost sinusoidal current, of a
variable magnitude, at point of connection. The
STATCOMs injected current is almost in
quadrature whit the line voltage, thus
emulating a capacitive or an inductive
reactance at a point of connection with line of
transmission.
SSSC
is
a
synchronous
series
compensator. It is work the same way as a
STATCOM. SSSC has a voltage source
converter that is serially connected to a
transmission line via a transformer. The
energy source is necessary to provide a
Fig.1: Basic Structure of SVC
The thyristor-controlled devices employs
reactor and capacitor banks with fast using
solid-state switches in conventional series and
shunt arrangement. The thyristor controlled
switches control the OFF and ON periods of
the fixed reactor bank and capacitor banks and
thus release a variable reactive impedance.
Besides for losses, thyristor controlled devices
cannot exchange real or active power with the
system.
SVC enables the fast control of reactive power in
the range of control. It has no inertia as compared
to synchronous condensers.
The SVC has one, more bank of switched
capacitors or reactors or fixed shunt capacitors
or reactors, of which thyristors is switched by
at least one bank. To make an SVC name of
the element are: Thyristor switched capacitor
(TSC), Thyristor controlled reactor (TCR),
mechanically switched reactors or capacitors
(switched by a circuit breaker), harmonics
filters(S), where the reactors may be ironcored or air cored.
In Fig .3, the one line diagram of a typical
SVC controller’s configuration is shown. The
Fig.2: Schematic Circuit Diagram of SVC
Fig.3: Line Diagram of Typical SVC Configuration
3 STATCOM (STATIC SYNCHRONOUS
COMPENSETOR)
The STATCOM static synchronous
compensator is shunt connected GTO based
Flexible Alternating Current Transmission
System device. It is a second-generation facts
controller device. STATCOM is also called
advanced SVC and then after Static
Condenser. The STATCOM controls the
voltage to the reference voltage level at the
connected bus by adjusting angle and voltage of
internal voltage source. The GTO is a selfcommuted power semiconductor device that is
used by VSCs. The other self-commuted power
semiconductor device used for the VSCs are
IGCT, MCT, IGBT (with higher cost).the
STATCOM device has the equivalent circuit similar
to synchronous condenser (SC). IT has some
advantage over to the synchronous condenser like
it’s symmetric lead-lag capacity and other
advantages. The STATCOM is a VSI (voltage
source
inverter)/VSC
(voltage
source
converter), which converts a given dc input
voltage into ac output voltage to compensate
the reactive and active power needed by the
system. It is a static synchronous generator,
which is operated as a static VAR
compensator, injects leading or lagging var
into the system. STATCOM use selfcommutated power semiconductor device and
SVC use thyristor devices that are variable
type that is why the STATCOM gives many
technical
advantages
over
the
SVC.
STATCOM have some advantages that are:

It has no rotating part.

Very fast in response.

Bulky passive components are
eliminated because it requires less
space.

No problem as loss of synchronism
and less maintenance.
Fig.4: Shunt Connected STATCOMS
STATCOMs simple diagram is shown in
Fig.4. STATCOM shows constant current
characteristics when voltage is low/high,
under/over the limit. Because of this reason,
STATCOM delivers constant reactive power as
compared to SVC. From the family of FACTS the
regulating devices, STATCOM can be used to
regulate the reactive power flow independently in
the system of the other parameters. It has no longterm energy support on the side of DC and with
the ac, system it cannot exchange the real
power.Fig.5 shows the connection of STATCOM to
the bus bar.
4 SSSC (STATIC SHYNCRONOUS SERIES
COMPENSETOR)
Now days, SSSC is one of the most important
and popular facts controller which is used for
series compensation of power. SSSC controllers
are the third generation FACTS controller devices.
It is a solid state VSI (voltage source inverter)/VSC
(voltage source convertor), which is inject
sinusoidal voltage of variable magnitude and in
series with the transmission line. The line current
is in quadrature with the injected voltage. The
basic SSSC diagram is shown in fig.6. In series
compensation the capacitor, which is connected in
series, compensates the inductive reactance of the
transmission line. The line current and SSSC
output voltage is in quadrature. The voltage across
series capacitor is –jXcI (where Xc is the
capacitive reactance of the series capacitor) and
voltage drop across line inductance (XL) is +jXLI
cancel each other thus reducing the effect of line
inductance. Due to this, power transfer capability
is Increased [9]. The basic representation of SSSC
using voltage source converter is shown in Fig.7
the SSSC operates as a series inductor and
controllable series capacitor. The basic difference
is that SSSCs injected voltage is not related to the
line intensity and it can be managed
independently. For this feature, the SSSC works
satisfactorily with lower load as well as high loads.
The SSSC has several advantages over the SVC
and STATCOM that are flows [10].
Fig.6: Series Connected SSSC


Fig.5: Connection of STATCOM to a
Busbar

It has improved technical characteristics.
Symmetrical capability in both capacitive
and inductive operating mode.
Possibility of connecting an energy source
on the DC side to exchange real power
with the AC network.
Fig.7: Schematic Diagram of SSSC
The SSSC has three basic components which
are:



VSC (voltage source converter). That is
main component.
Table.1 - Cost Comparison of FACTS Devices
S.no.
Energy source. Compensate for device
losses and providing voltage across the dc
capacitor.
5 COST COMPARITION OF VARIOUS FACTS
DEVICES
We know that the fact devise is used mainly
for reactive power compensation. The Table .1,
[11].gives the various facts devise. If the devices
are costly then it provides smooth and fast
response for securing the power system network
burring the steady and normal state operation, it
is the main advantage of the costly and
expensive
FACTS
devise.
Flexible
ac
transmission system controllers may be based
on power devices with gate turn off or thyristor
devices with no gate turn off capability. The
FACTS controllers are used for the dynamic
voltages control, phase angle and impedance of
high voltage ac transmission. The facts
instruments can save or secure the system from
potential risk of system collapse, which can have
much serious consequences on the other
economic sector as well. If the technology is
better than the cost is higher and it can avoid the
blackout conditions. hence the cost of the facts
devices controllers is considerate.
The cost /var go down as the capacity of
FACTS controller increases. The total cost is
depending on the size of controlled and fixed
portion of the FACTS devices. The cost of the
FACTS devices shows the half cost of the total
cost of fact project.
Cost (Rs/var)
Shunt
capacitor
Series
capacitor
1
Transformer. Coupling transmission line and
SSSC.
Facts
devices
2
432
1080
3
SVC
2160 (controlled
portion)
4
STATCOM
2700
The Table 2 gives the FACTS devices main
function and there controlled element. From the
Table 2, we can see that the controlling element
of the svc is thyristor which is first generation
FACTS device and the STATCOM and SSSCs
controlled element is GTO which are the second
generation FACTS devices that gives better
performance as compared to the SVC, hence
the cost of the SSSC and STATCOM is higher
than the SVC.
Table 2 –The main function of FACTS
devices SVC, STATCOM and SSSC
S.
no.
Name
Type
Main
function
Contr
oller
1
SVC
Shunt
Voltage
control
Thyris
tor
2
STATCO
M
Shunt
3
SSSC
Series
Voltage
and
reactive
power
Power
flow
control
GTO
GTO
6 DEVICE CAPABILITY
The Table 3 gives different types of FACTS
devices capability differences. Here we can
compare
SVC,
STATCOM
and
SSSC
capabilities. From the Table 3, it is investigated
that the SSSC is the effective device for power
flow control, transient stability, voltage stability,
for power oscillation damping and high
transmission capacity. However, the cost of the
SSSC is higher than the SVC and STATCOM
devices.
Table 3- FACTS Devices SVC, STATCOM and
SSSC Capabilities
S.
N
o
1
2
3
4
5
6
7
Device
Capabilities
Transmission
capacity
Power flow
control
Transient
stability
Voltage
stability
Power
oscillation
damping
Of wind farmer
active power
o/p
Investment
Cost
SVC
STATCOM
Small
Small
Small
Small
Small
Medium
Strong
Strong
Medium
Medium
7.2 Congestion management application
In present deregulated electricity market,
the congestion management is a serious trouble
for independent system operator (ISO) as it can
illogically increase the prices. The FACTS
devices like SSSC can help to reduce the
congestion, smoothen location marginal prices
(LMP) and to increase social welfare by
redirecting power from congested interface to
underutilized lines.
7.3 ATC (Available
improvement)
transfer
capability
Some of the deregulated market the power
transaction between seller and buyer is based
on ATC calculation. Low ATC shows that the
network is unable to adjust further transaction
and that is why they do not promote free
competition. The FACTS controllers like
STATCOM and SSSC improve ATC by allowing
more power transaction.
7.4 Reactive power and voltage control
We know that the shunt controlled FACTS
devices like SVC and STATCOM is used for
reactive power and voltage control and SSSC
used for the reactive power, active power and
the voltage control that is SSSC is better than
the SVC and STATCOM.
7.5 Loading margin improvement
Yes
Yes
Small
medium
7 APPLICATIONS
In the last two decades, researchers
developed new algorithms for solving the
optimal flow problem incorporating various
FACTS devices [12]. Table 4 shows the
application of SVC, STATCOM and SSSC.
The thyristor-controlled FACTS like those that
SVC is modeled as controllable impedance.
However, VSC based FACTS devices like SSSC
and shunt devices like STATCOM are complex
and usually modeled as Controllable sources
that is more complex. Now a day the SSSC is
used for many application as compared than the
SVC and STATCOM.
7.1 Steady state application
FACTS controller for various steady state
applications includes post-contingency voltage
control, voltage control (high and low) loop flow
control, and increase of thermal loading, short
circuit level reduction and control of power flow.
The SVC and STATCOM is used for voltage
control and SSSC is used for power flow control
and loop flow control.
In many part of the world the several
blackouts occurs mainly due to voltage collapse
at the maximum load ability point. The shunt
compensation devices like SVC and STATCOM
and series compensation devices like SSSC are
generally used to increase the maximum transfer
capabilities of power networks.
7.6 Power flow balance and control
The FACTS controllers like SSSC enable
the load flow on different voltage levels and the
parallel circuits to be controlled and optimized,
with minimum of power control. Hence the best
utilization of the lines and a reduction of overall
system losses at the same time.
7.7 Dynamic application
FACTS controllers’ dynamic application
includes dynamic stability (oscillation damping),
transient stability improvement and voltage
stability enhancement. The very important
property of the facts devices is to reduce the
primary disturbance. The impact reduction for
contingencies can be achieved by STACOM and
SSSC.
7.8 Transient stability enhancement
The large disturbances are the causes of
transient instability. The large disturbances are
from tripping of a generator or a transmission
line. We can see the problem from the first swing
of the angle. The facts devices like SVC,
STATCOM, and SSSC can resolve this problem
by providing rapid and fast response during first
swing to control voltage and power flow in the
system.
7.11 Power system interconnection
In all over the world the power exchange
between one country to other countries as well
as regions within the countries the large
interconnected system is used. There are many
examples of interconnection of remotely
separated regions within one country. Those are
found in north countries like Brazil and
Argentina. After the invention off the STATCOM
and the SSSC potential as well as the flexibility
is added to ac power system.
7.9 Oscillation damping
All over the world the electromechanical
oscillations have been observed and may cause
partial power interruption if it is not controlled.
Hence for the oscillation damping in the power
system we use power system stabilizer (PSS).
This property can be achieved by proper
placement and setting of SVC, STAATCOM, and
SSSC. The SSSC is more effective then the
SVC and STATCOM.
7.12 Application in deregulated environment
Apart from the facts tradition application for
power flow control, voltage control, enhancing
steady stat and dynamic limits they are finding
new application in the today’s deregulated
environment. One application is loop flow or
parallel flow. Parallel flow results in reduction in
Trans mission capacity but it has some utilities.
The series compensated device like SSSC have
loop flow feature.
7.10 Dynamic voltage control
The facts shun controller like SVC and
STATCOM can be used for the dynamic control
of voltage at the time of contingency and save
the system from blackout and voltage collapse.
Table 4 – Application of FACTS Device SVC, STATCOM and SSSC
S.no
Subject
Problem
Corrective action
FACTS
1
Voltage
limits
Low voltage at heavy load
Supply reactive power
SVC,
STATCOM
2
Voltage
limits
high voltage at low load
Absorb reactive power
SVC,
STATCOM
3
Voltage
limits
high voltage following on
outage
Absorb reactive power, prevent
overload
SVC,
STATCOM
4
Voltage
limits
low voltage following on
outage
Supply reactive power, prevent
overload
SVC,
STATCOM
5
Thermal
limits
Transmission circuit overload
Increase transmission capacity
SSSC
6
Load flow
Load flow reversal
Adjust phase angle
SSSC
7
Load flow
Power distribution on parallel
lines
Adjust line reactance and
phase angle
SSSC
8
Stability
Limited transmission power
Decrease the line reactance
SSSC
The facts another application is to use
facts to relive the confection in the network
system. FACTS devices are strategically
placed such that curtailment is decreased,
price volatility due to congestion is minimized
and cost is reduced.
8 CONCLUSIONS
In this paper we compared the SVC,
STATCOM and SSSC on the basis of cost,
dynamic stability, steady state stability, load
flow, loop flow, power flow control, reactive power
control, active power control and voltage control
and we get that the SSSC is gives the better
response as compared to the other two FACTS
devices namely SVC and STATCOM. Here we
also see that the SSSC is costly than the SVC and
STATCOM but it is beneficial than the SVC and
STATCOM. SVC is only control the reactive power
,STATCOM control the reactive power and voltage
where as the SSSC is control the active power,
reactive power and the voltage control. Instead of
using bulky devices like SVC and STATCOM,
only SSSC is beneficial for the smooth
operation of Power Quality Improvement and
regulation purpose.
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Author’s Biography
Ms. Poonam Pandey was born
at Chhattisgarh and received her
B.Tech degree in ET&T from
Central Institute of Technology,
Raipur,
Chhattisgarh,India
in
2013. Currently she is pursing her
M.Tech degree in Electrical
Engineering at the ITM University, Chhattisgarh,
India. Her area of interest is Power Transmission
and Distribution
Mr. Siraparapu Satyanarayana
was born at Andhra Pradesh. He
received his B.Tech degree in
EEE from Jawaharlal Nehru
Technological
University
Kakinada, India in 2012. He
received his M.Tech degree in
Electrical Engineering at the Lovely Professional
University, Punjab, India in 2014. He has
published 5 papers in International Journals. His
area of research includes Power Systems and
Automatic Generation Control in Power Plants.
Currently working as a Assistant Professor in
Electrical Engineering Department at ITM
University Raipur.