POSTER 2015, PRAGUE MAY 14
1
Comparison of the Operational Theory and
Features of SVC and STATCOM
Arun Singh SENGAR1, Raunak CHHAJER2 , Ghaeth FANDI3, Famous O. IGBINOVIA4
1,3,4
Dept. of Electrical Power Engineering, 2Dept. of Cybernetics, Czech Technical University, Technická 2, 166
27 Prague, Czech Republic
sengaaru@fel.cvut.cz, chhajrau@fel.cvut.cz, fandigha@fel.cvut.cz, igbinfam@fel.cvut.cz
Abstract. This paper presents a comparison of the
operational theory and features of Static Var Compensator
(SVC) and Static Synchronous Compensator (STATCOM)
in power system networks. It compares the Voltage
Regulation, System Stability, Economical and Harmonics
of these devices. The comparison shows that both devices
are promising in enhancing voltage stability and increases
transmission capacity in power system. And it also shows
that STATCOM has the ability to provide more capacitive
power during fault situation over SVC. Hence, STATCOM
exhibits faster response than SVC.
Keywords
Reactive Power, SVC, STATCOM, Voltage Control,
Power System Stability
1.
Introduction
In an AC circuit, the power transferred, which is the
Apparent Power, can be defined as a product of two power
components: Active power, also known as Real/True
Power, this is the power drawn by the electrical resistance
of an electrical system for doing useful work. It is
measured in watts or W [1]. Reactive Power, also known as
use-less/watt-less power, is the power merely absorbed and
returned in load due to its reactive properties; in this case,
energy is first stored and then released in the form of
magnetic or electrostatic field in inductors and capacitors.
It is Measured in Volt-Ampere reactive or VAR) [2].
Fig 1: Power Representation [3].
The measurement of the efficiency of power system is
given by the power factor,
.Hence, in order to improve
the power of an alternating power system, management of
the resistive power is required. This can be achieved by
Reactive Power Compensation, which is usually referred to
as VAR compensation. And one way of doing this is by
using a device called Synchronous Condenser or
Synchronous Compensators.
Fig 2: Measurement of Power Factor [3].
Synchronous Compensators are synchronous motors which
are run without any load. These motors are used to
generate or absorb reactive power from an electrical power
ARUN SINGH SENGAR, RAUNAK CHHAJER, GHAETH FANDI, FAMOUS OGHOMWEN IGBINOVIA
system. It is generally located near large loads, these
motors, running in the over-excited condition provide
reactive power according to the load demand. While static
reactors and capacitors can be used in reactive power
regulation in lines, synchronous compensators have the
advantage of quick responses and fine control depending
on the excitation.
Amongst reactive power compensators devices available
today, SVC and STATCOM seems to be most talked about.
Hence in this paper, the working principles of operation of
these two devices are compared, in order to highlight their
respective advantages and disadvantages over each other.
2.
Operational Theory of Static VAR
Compensator (SVC)
Fig 4: the diagram of a TCR and TSR [6].
The current ITCR is directly related to the firing angle
of the thyristor (α), which is varied between 90° and 180°
[5], [6], [7].
The value of the substance BTCR is represented by the
equations given below; [4], [5], [7], [8].
 2 1

  -  sin (2 )
BTCR( )  BLmax 1 -
(1)
Where BLmax = 1/L 
Whereas BTCS is defined as-


BTCS  Bc max 1 
2


1

sin (2 )
Where Bcmax = - C 


(2)
3.
Features of the Static VAR
Compensator (SVC)
Fig 3: Structure of SVC Device [4].
The Diagram in figure 3 shows an SVC Device
containing a pair of TCR (Thyristor Controlled Rectifier)
and TSC (Thyristor Switched Capacitor) connected in
Parallel. This model is connected to a HV Line in parallel
through a Shunt Transformer [4]. The SVC controls
voltage where it is connected by adjusting it in order to
supply or absorb the required reactive power [5]. An
associated Controlling System operates to control the
Voltage at its Connecting Point, according to its regulating
Scheme within the allowed operational limits.
The purpose of the Thyristor Controller in each
branch of SVC is to enable the connected reactive element,
which is the Inductor of TCR and the Capacitor of TSC, to
act as a controllable device, which is achieved by
appropriate firing Angle α of each respective Thyristor.
Figure 4 (a) and (b) shows the illustration of TCR and TSC
respectively.
Fig 5: SVC V-I features [5].
If the value lies between Bcmax (for Capacitor) and Bimax
(for Inductor), the voltage is regulated at the reference
voltage Vref. Practically, Voltage drop between the range of
1% and 4% at maximum reactive power output is used and
hence the V-I feature is as shown in figure 5 above [5].The
equations for V-I feature are as follows; [9].
POSTER 2015, PRAGUE MAY 14
3
V  Vref  Xs.I
if SVC is in regulation range (−Bcmax<B<Bi max)
(3)
V2- Line to line voltage of source 2
V  - I/Bcmax
(4)
(5)
Where-
I = Reactive current (pu/Pbase) (I > 0 indicates an
inductive current)
Xs = Slope or droop reactance (pu/Pbase),
Bcmax = Maximum capacitive (pu/Pbase) with all TSCs in
service, no TSR or TCR,
=
During the steady state operation the voltage V2
generated by VSC (Voltage Source Convertor) is in phase
with V1 and hence δ=0, due to which there is no active
power (P=0) and hence only reactive power is flowing.
If V2<V1 – Reactive Power (Q) is flowing from V1
to V2 (STATCOM Absorbs reactive power)
V= Positive sequence voltage (pu),
Bi max
X- Reactance of interconnection transformer and
filters
δ - Phase angle of V1 with respect to V2
if SVC is fully capacitive (B=Bcmax)
V  I/BImax
if SVC is fully inductive (B=Blmax)
V1- Line to line voltage of source 1
If V2>V1 – Reactive Power (Q) is flowing from V2
to V1 (STATCOM injects reactive power)
The Capacitor connected to VSC, can adjusts its
Voltage as required and hence works as Voltage source for
it. For Steady State, the Voltage V1 and V2 must have a
slight phase difference, which is to say that V2 should be
lagging, in order to keep the Capacitor charged and also to
compensate for the VSC and transformer losses [9].
Maximum inductive (pu/Pbase) with all TSRs in
service or TCRs at full conduction, no TSC,
Pbase = Three-phase base power specified in the block
dialog box [9].
5.
Static Synchronous Compensator
STATCOM (V-I) Features
4.
Operational Theory of Static
Synchronous Compensator
(STATCOM)
Fig 7: STATCOM V-I Feature [9].
If the Reactive Current lies within the maximum Inductive
and maximum Capacitive Current Values (-Imax, Imax),
voltage remains regulated at the Reference Value of Vref.
Practically a Voltage drop in the range of 1% and 4% at
maximum reactive power output is used, hence the V-I
feature, is as shown in figure 7. The equations for V-I
feature are given as follows; [9].
Fig 6: Operation of STATCOM [9].
The diagram shows a STATCOM and a Transmission
Line for which-
V  Vref  XsI
(8)
Where - V = Positive Sequence Voltage
P  V1V2 sin  / X
Q  V1 (V1 - V2 cos )/X
(6)
(7)
I = Reactive current (pu/Pnom)
(I > 0 indicates an inductive current)
Xs = Slope or droop reactance (pu/Pnom)
Where P - Active Power
Q - Reactive Power
Pnom = Three-phase nominal power of the converter
specified in the block dialog box [9].
ARUN SINGH SENGAR, RAUNAK CHHAJER, GHAETH FANDI, FAMOUS OGHOMWEN IGBINOVIA
6.
Comparison of SVC and
STATCOM
6.1
Voltage Regulation
As has been seen in its operational theory, SVC does not
have impact on the transmission network directly; it is
connected as shunt impedance in order to produce the
required compensating current. The provided shunt
compensation depends on the prevailing line voltage [10].
Under normal System Condition SVCs are often operated
as floating with Zero reactive power output, but it readily
respond to a fast Voltage Control action during crucial
disturbances. However, the reactive power injection or
voltage regulation capability of SVC is limited by the value
of its reactance and it is line voltage dependent [11], [12].
SVCs are ideally suited to control the varying reactive
power demand of large fluctuating loads and the over
voltage dynamics due to load rejection. With rapidly
varying loads, reactive power demand can be speedily
corrected by SVC, with small overshoots and voltage
rising. From the V-I feature in Figure 5; the linear
dependence of the obtainable current from the system
voltage is seen. For terminal voltage changes outside the
control range, SVC feature becomes fixed. By decreasing
the system voltage, the voltage support capability of the
SVC rapidly deteriorates [9], [10]. The maximum reactive
power generation or absorption is dependent on the
alternating current system voltage.STATCOM is also a
shunt connected device to a power system, and can also be
considered as a voltage source behind a reactance, which
generate/absorb reactive power. Unlike SVC, STATCOM
typically consists of a direct current to alternating current
converter employing solid state power electronic switching
devices and a set of converter controls varying the
STATCOM output. It provid
es
reactive
power
generation and absorption with electronic processing of
voltage and current waveforms in a voltage source
converter [13], [14]. STATCOM can provide a capacitive
and inductive output current over the rated maximum
capacitive and inductive current range independent of the
system voltage, the output current of the STATCOM is
substantially independent of the power system voltage and
the equivalent impedance at the point of connection, it
provides reactive power that decreases linearly with system
voltage. This characteristic makes the STATCOM more
robust and effective than SVC in providing voltage support
and controlling specific parameters of an electrical power
system. [13], [15], [16].
6.2
additional control methods with complementary circuits are
used. Studies have shown that Harmonics are less in
STATCOM compared to SVC [21].
Harmonics
SVC and STATCOM are not free from Harmonics
and hence, different filter mechanisms are used to reduce
the Harmonics. To reduce Harmonics in SVC multilevel
pulse width modulation (PWM), and 3 levels Inverter
technique, is used [17], whereas in the case of STATCOM,
6.3
Economical Aspects:
: It is so obvious that FACTS controllers are very
expensive compared to the conventional old devices like
Capacitor Bank, Synchronous Condenser etc. Table 1:
shown below gives a comparative view of the cost of Shunt
controllers [18], [19].
Shunt controller
Cost (US $)
Shunt capacitor
8/kvar
SVC
40-60/kvar
portion)
(controlled
STATCOM
55-70/kvar
portion)
(controlled
Table 1: Cost comparison of shunt controllers [18], [19].
As we know from the operational theory of
STATCOM, it does not only controls, but also internally
generates capacitive and inductive reactive power outputs,
large capacitor and reactor banks with their associated
switchgear and protection, used in conventional thyristorcontrolled SVCs are not needed. This results in a
significant reduction in overall size (about 30 to 40%), as
well as in installation labour and cost. The small physical
size of the STATCOM makes it eminently suitable for
installations in areas where land cost is at a premium, and
for applications where anticipated system changes may
require the relocation of installations [9].
Due to lower space requirements, low switching
frequencies, and better performance, STATCOM is
expected to be a better economical option.
6.4
Stability Of the System:
Although SVC fulfils the same task as STATCOM,
but due to its advanced technology and better performance,
STATCOM has been found to be more effective than SVC
in ensuring voltage stability. Under distorted main voltage
conditions STATCOM can provide more reactive power
for keeping the voltage near referenced value. The ability
to provide more reactive power during fault situations is
one of the most important advantages of the STATCOM
over the SVC, which helps for faster recovery of the
system during faults situations. STATCOM normally
exhibit a faster response than SVC, because of the voltage
source converter technology, that has no delays associated
with the firing of its thyristors. Under distorted main
voltage conditions STATCOM can provide more reactive
power for keeping the voltage near referenced value. Both
POSTER 2015, PRAGUE MAY 14
5
reactive compensators have different working principles,
but the impact on increasing network stability is
comparable.
7.
General Evaluation of SVC and
STATCOM:
Evaluation of SVC and STATCOM devices is shown in
table 2 below [20], [21].
Criteria
SVC
STATCOM
Operating principle
Controlled shunt
impedance
Controlled voltage
source
Reactive power
regulation
±100 MVAr
2x ±50 MVAr
Space requirement
Large (60x85 m2)
Smaller then SVC
(59x45 m2)
Pack solution
Open pack
solution
Containerized
solutions
Dependency of the
current output
from the voltage
level in the point of
connection
Linear
Non-Linear
Dependency of the
reactive power
output from the
voltage level in the
point of connection
Quadratic
Reactive Power
generation during
the three phase
short circuit
scenario
Low
Overload capability
No
Yes (±25%In for 1 s)
Response time
Fast
Faster than SVC for
30 ms
Maintenance and
service
requirements
High
Low
Cost
from $40 to $60
per kvar
$55 to $70 per kvar
reactive power generation and absorption with electronic
processing of voltage and current waveforms in a voltage
source converter. The over-current protection is also
provided to restrict high currents during high voltages to
prevent damage of converter thyristors. Initial installation
cost of STATCOM is a bit higher compared to SVC but the
maintenance cost and complete Life Cycle cost make it
more economical option compared to SVC.
It is a wise step to evaluate both STATCOM and SVC in
terms of their features, in order to know when to
appropriately apply each device in an electrical network.
Acknowledgements:
The research described in this paper was supervised
by Ing. Jan Švec, Ph.D. and Prof. Ing. Josef Tlusty CSc,
FEE CTU in Prague and supported by the Czech Grant
Agency under grant SGS14/188/OHK3/3T/13.
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8.
Conclusion:
A study of the comparison of STATCOM and SVC based
on various features has been made. Merits and Demerits of
using STACOM and SVC have been discussed in details.
SVC and STATCOM both increase the static voltage
stability margin and power transfer capability of power
systems. However, STATCOM provides better behaviour
in terms of loss reduction and voltage profile. Harmonics
are more in SVC compared to STATCOM. It provides
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About Authors:
Arun Singh Sengar was born in India and holds a
Bachelor of Engineering degree in Electrical and
Electronics Engineering from Govt. Engineering College,
Bhopal (UIT RGPV), India. Currently, he is a master’s
student at the Department of Electrical Power Engineering,
Faculty of Electrical Engineering, Czech Technical
University in Prague, Czech Republic.
Raunak Chhajer was born in India and holds a Bachelor
of Technology’s degree in Computer Science and
Engineering from West Bengal University of Technology.
Currently, he’s pursuing a master’s program in Robotics at
the Department of Cybernetics and Robotics, in the Faculty
of Electrical Engineering at Czech Technical University in
Prague, Czech Republic.
Ghaeth FANDI graduated from Tishreen University,
Latakia, Syria, where he got his Master of Engineering
Degree in Electrical Engineering. He also holds a Master
degree in Renewable Energy from the same University.
And is currently a Doctorate (PhD) student in the
Department of Electrical Power Engineering at Czech
Technical University in Prague, Czech Republic.
Famous Oghomwen IGBINOVIA received his Bachelor
of Engineering (B.Eng) degree in Electrical/Electronics
Engineering from Ambrose Alli University, Ekpoma,
Nigeria and also received a Master of Engineering (M.Eng)
degree in Power and Machines from the University of
Benin, Benin City, Nigeria. He is currently a Doctorate
(PhD) student in the Department of Electrical Power
Engineering at Czech Technical University in Prague,
Czech Republic.