Imperial Journal of Interdisciplinary Research (IJIR)
Vol-2, Issue-5, 2016
ISSN: 2454-1362, http://www.onlinejournal.in
Improving Power Quality of a
Transmission Line using Static VAR
Compensator
Rubi Kumari & Ipsita Das
Sikkim Manipal Institute of Technology
Abstract: In this paper improvement of power quality
and efficiency of transmission line has been discussed
using Static VAR Compensator (SVC). The Matlab
Simulink model of SVC addressed here comprises of
Thyristor Switched Capacitor (TSC) and Thyristor
Controlled Reactor(TCR) which gave the enhanced
results in terms of voltage , current and improved
power quality in the transmission line.
1. Introduction
Over the last few years, power quality has been an
important issue in the field of power system. Need of
rapid dynamic response, ability to adapt the frequent
variations in output and smooth adjustable output, an
improvement of voltage flicker in power transmission
has led to the use of FACTS devices. Among various
FACTS devices the SVC plays an important role in
regulation of voltage and improvement of power
transfer capability in power system. There are two
main applications of SVCs:Transmission SVC: - They are connected to power
system to regulate the transmission voltage
Industrial SVC:-They are connected near large
industrial loads, to improve power quality.
reference voltage. The load line B intersects the SVC
characteristics at voltage V2. Since voltage V2 is
above the reference voltage, the reactive power needs
to be absorbed from the system (indicates inductive
reactive power is required). The current I1 corresponds
to voltage V2 in the inductive region and therefore it
requires the operation of the Thyristor Controlled
Reactor (TCR) . The load line C intersects the SVC
characteristics at a voltage V1 which is below the
reference voltage and hence reactive power needs to be
provided to the system (capacitive reactive power is
required). Thus the current I2 corresponding to voltage
V1 is in the capacitive region of operation [1].
Figure 1. V- I Characteristics of the SVC
1.1. SVC
1.2. TCR
It is series compensated power electronics device
which provides fast acting reactive power on high
voltage electricity transmission network. SVCs either
absorb or supply reactive power based on the change of
VAR requirement of the load. Thus SVC provides
power factor correction to maintain the unity power
factor at variable loads. In this paper SVC has been
modeled using TSC and TCR.
The SVC can be operated in two different modes: In
voltage regulation mode and in VAR control mode (the
SVC Susceptance is kept constant).
The system characteristic is represented by the load
line A which intersects the SVC characteristics at
Imperial Journal of Interdisciplinary Research (IJIR)
The TCR is a Thyristor Controlled Reactor whose
effective reactance can be varied continuously by
partial conduction control of thyristor valve [2,3].The
basic principle of TCR is to control the reactive power
by controlling the firing angle of the thyristor valve.
The controlled element is the reactor and the
controlling element is the thyristor controller consisting
of two oppositely poled thyristors which conducts at
every alternate half cycles of the supply frequency [4].
Page 180
Imperial Journal of Interdisciplinary Research (IJIR)
Vol-2, Issue-5, 2016
ISSN: 2454-1362, http://www.onlinejournal.in
Figure 2 . Thyristor controlled reactor (TCR)
The Simulink Model of the test system as shown in
Figure 4, comprises of the three phase source from
where 11kV is being generated. The 11kV has been
then stepped up to 33kV using three phase transformer
under a three phase Pi (∏) section of 10 KM. Further
the phase voltage has been stepped down to 11kV with
an apparent power of 20 MVA. Three parallel loads are
connected with respective active and reactive power at
0.8 p.f lagging.
1.3. TSC
The circuit diagram of Thyristor Switched Capacitor
(TSC) is shown in Figure 3. Each thyristor valve
consists of two oppositely poled thyristors. The
thyristor valves are delta connected in order to
eliminate zero sequence harmonics (3rd, 9th….).The
harmonics remain trapped inside the delta and thus
reduce harmonic injection into the power system.
When thyristor is switched ON under abnormal
operating condition reactor L limits the surge current.
As compared to the mechanically switched capacitors ,
TSC provides instantaneous response to the changes
occurring in the system parameters and hence more
reliable [1].
Figure 5. Simulink model of SVC
Figure 3. Thyristor Switched Capacitor (TSC)
2. Modeling of SVC
Fig
Figure 6. Simulink model of SVC controller
SSSS
Figure 4. Single line diagram of SVC model
Imperial Journal of Interdisciplinary Research (IJIR)
The SVC controller has been designed in this paper
to maintain the system voltage at 33 kV bus. If the bus
voltage decreases, the SVC will inject reactive power
(Q) into the system and if the bus voltage increases the
SVC will absorb the reactive power to the system. The
Simulink diagram of SVC controller is shown in Figure
6.
Page 181
Imperial Journal of Interdisciplinary Research (IJIR)
Vol-2, Issue-5, 2016
ISSN: 2454-1362, http://www.onlinejournal.in
3. Results and Discussion
3.1. Voltage, Current and Power profile
without the SVC controller
To introduce disturbance in the three - phase power
system, transient time 2 s and 4 s in the three – phase
breakers has been considered. One of the breaker was
connected in series and the other in parallel to the
transmission line. The voltage, current and power drop
due to the connected load was observed as shown in
Figure 7, Figure 8, Figure 9 and Figure 10 respectively.
3.2. Voltage, Current and Power profile with
the SVC controller
To overcome the disturbance at 2 s and 4 s, the SVC
controller has been connected to the three - phase
transmission line. Once the SVC has been introduced,
the effect in the voltage, current and power profile of
the designed power system has been shown in Figure
11, Figure 12, Figure 13 and Figure 14 respectively.
Figure 11. Voltage profile with SVC
connected to the transmission system.
Figure 7. Voltage profile without SVC
connected to the transmission system.
Figure 12. Current profile with SVC
connected to the transmission system.
Figure 8. Current profile without SVC
connected to the transmission system.
Figure 13. Active power profile with SVC
connected to the transmission system.
Figure 9. Active power profile without SVC
connected to the transmission system.
Figure 14. Reactive power profile with SVC
connected to the transmission system.
Figure 10. Reactive power profile without
SVC connected to the transmission system.
Imperial Journal of Interdisciplinary Research (IJIR)
Page 182
Imperial Journal of Interdisciplinary Research (IJIR)
Vol-2, Issue-5, 2016
ISSN: 2454-1362, http://www.onlinejournal.in
4. Conclusion
In this paper, the basic structure of a SVC, operating
under bus voltage and its model has been addressed.
The model has been designed as a controller with
variable impedance that changes with the firing angle
of the TSC and TCR. Disturbances at 2 s and 4 s has
been introduced such that the designed SVC could
mitigate the problem of voltage, current and power
drop at 2 s and 4 s respectively. Therefore, the
designed SVC could successfully control the voltage
and stabilize the power system at the point where it has
been connected to the system.
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Imperial Journal of Interdisciplinary Research (IJIR)
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