International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE)
ISSN: 0976-1353 Volume 14 Issue 2 –APRIL 2015.
Stability analysis of the Power System Network
using FACTS Controller
FATIMA KUDCHI
Assistant professor , Departement of Electrical and Electronics Engineering,B.L.D.E.A’ CET ,College of
Engineering and Techonology,Bijapur-586101.Karnataka.India
naveed_kudchi@rediffmail.com,fatima2109@yahoo.com
Abstract: The demand of Electric energy increases
continuously with the increasing size and complexity of the
transmission networks, the performance of the power
systems decreases due to problems related to load flow,
voltage stability and others, FACTS is one of the growing
technology uses power electronics control devices for
existing power system network. SVC is one of the facts
device which plays an important role in controlling the
reactive and active power flow to the power network and
hence both the system voltage fluctuations and transient
stability. In recent years, FACTS technology has been
considered as one of feasible planning alternative in India,
to increase power grid delivery capability and remove
identified network bottlenecks. The aim of applying
reactive Shunt compensation is to increase the
transmittable power in line. Here an attempt is made in
this paper for studying the aspects of SVC, and Simulation
of SVC, using SIMULINK for analyzing the voltage
regulation and also the fault studies.
Keywords: Flexible AC Transmission Systems ,SVC,
Voltage Stability,THD,Fault analysis,MATLAB
I.Introduction:
Successful operation of a power system depends
largely on the engineer's ability to provide reliable and
uninterrupted service to the loads. The first requirement
of reliable service is to keep the synchronous generators
running in parallel and with adequate capacity to meet
the load demand (Etap paper). The potential benefits of
using the FACTS controllers for enhancing power
system stability are well known.An inherent
characteristic of electric energy transmission and
distribution by alternating current (AC) is that real
power is generally associated with reactive power. AC
transmission and lines are dominantly reactive networks,
characterized by series inductance and shunt
capacitance. Thus, load and load power factor changes
alter the voltage profile along the transmission lines
Most of loads are not tolerant to voltage variation.
Under voltage causes degradation in the performance of
load[1]. Reactive power also increases transmission
losses. Power System Stability is the ability of the
system to regain its original operating conditions after a
disturbance to the system. Power system transient
stability analysis is considered with large disturbances
like sudden change in load, generation or transmission
system configuration due to fault or switching [2].
Dynamic voltage support and reactive power
compensation have been identified as a very significant
measure to improve the transient stability of the system.
1.1 Overview of FACTS:
In the late 1980s, the Electric Power Research
Institute (EPRI) formulated the vision of the Flexible
AC Transmission Systems (FACTS) in which various
power-electronics based controllers regulate power flow
and transmission voltage and mitigate dynamic
disturbances. Generally, the main objectives of FACTS
are to increase the useable transmission capacity of lines
and control power flow over designated transmission
routes. There are two types for realization of power
electronics-based FACTS controllers: the first
generation employs conventional thyristor-switched
capacitors and reactors, the second generation employs
gate turn-off (GTO) thyristorswitched converters as
voltage source converters (VSCs). The first generation
has resulted in the Static Var Compensator (SVC), the
Thyristor- Controlled Series Capacitor (TCSC), and the
Thyristor-Controlled Phase Shifter (TCPS). The second
generation has produced the Static Synchronous
Compensator.Typically, an SVC comprises one or more
banks of fixed or switched shunt capacitors or reactors,
of which at least one bank is switched by thyristors.
Elements which may be used to make an SVC typically
include:

Thyristor controlled reactor (TCR), where the
reactor may be air- or iron-cored

389
Thyristor switched capacitor (TSC)
International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE)
ISSN: 0976-1353 Volume 14 Issue 2 –APRIL 2015.

family using power electronics to control power flow
and improve transient stability on power grids [2]. The
SVC regulates voltage at its terminals by controlling the
amount of reactive power injected into or absorbed from
the power system. When system voltage is low, the SVC
generates reactive power (SVC capacitive). When
system voltage is high, it absorbs reactive power (SVC
inductive). The variation of reactive power is performed
by switching three-phase capacitor banks and inductor
banks connected on the secondary side of a coupling
transformer. Each capacitor bank is switched on and off
by three thyristor switches (Thyristor Switched
Capacitor or TSC). Reactors are either switched on-off
(Thyristor Switched Reactor or TSR) or phasecontrolled (Thyristor Controlled Reactor or TCR). Fig.1
shows a single-line diagram of a static var compensator
and a simplified block diagram of its control system.
Harmonic filter(s)

Mechanically switched capacitors or reactors
(switched by a circuit breaker)
By means of phase angle modulation switched by the
thyristors, the reactor may be variably switched into the
circuit
and
so
variable MVAR injection
provide
(or
a
continuously
absorption)
to
the
electrical network. In this configuration, coarse voltage
control is provided by the capacitors; the thyristorscontrolled reactor is to provide smooth control.
On the platform of SIMULINK, a worldwide-used
simulation tool for power system analysis, the electric
power system is settled up for the modeling of
Transmission Line , and setup for the calculation of the
various parameter for the stability assesment of the
power system. With the multiple voltage levels in the
system, voltage profile is sensitive to the system
structure and operation point. It is critical for the case
that most of the loads are large motors. Although the
system is connected to the bulk system under normal
condition, it may operate isolated at extremely fault
contingency.
Smoother control and more flexibility can be provided
with thyristors-controlled capacitor switching.[
II. Static VAr Compensator:
By definition, capacitors generate and reactors
(inductors) absorb reactive power when connected to an
ac power source. They have been used with mechanical
switches for (coarsely) controlled var generation and
absorption since the early days of ac power
transmission. Continuously variable var generation or
absorption for dynamic system compensation was
originally provided by .over- or under-excited rotating
synchronous machines and, later, by saturating reactors
in conjunction with fixed capacitors[3] a static var
compensator (SVC) is, by the IEEE CIGRE codefinition, a static var generator whose output is varied
so as to maintain or control specific parameters (e.g.,
voltage, frequency) of the electric power system[3].
The aim of this study is to analyze the Stability of
the Transmission system under Varying line length of
the Transmission Line. Section II is the development of
the system model of the SVC. Section III assesment of
the Voltage Regulation, Real and Reactive Power,Total
harmonic Disortion, Efficiency of the System under
varying line length Section IV . describes the results for
the above section . Section VI concludes the paper
2.1 The Thyristor-Controlled(TCR):
A TCR is one of the most important building block of
thyristors based SVCs.it can be used alone ,it is more
often employed in conjunction with fixed or thyristors
switched capacitor to provide rapid, continuous control
of reactive power.An elementary single-phase thyristorcontrolled reactor (TCR) is shown in Fig1. The basic
single phase TCR comprise an anti-parallel connected
pair of thyristors valve T1 and T2 in series with a linear
air core reactor, shown in
The Static Var Compensator (SVC) is a shunt device
of the Flexible AC Transmission Systems (FACTS)
390
International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE)
ISSN: 0976-1353 Volume 14 Issue 2 –APRIL 2015.
fig.The basic modeling of single phase TCR can be as
follows the source voltage as
applied voltage v and the reactor current iL(a), at zero
delay angle (switch fully closed) and at an arbitrary a
delay angle, are shown. When α = 0, the valve sw closes
at the crest of the applied voltage and evidently the
resulting current in the reactor will be the same as that
obtained in steady state with a permanently closed
switch. When the gating of the valve is delayed by an
angle a (0 -s α -s 1T/2) with respect to the crest of the
voltage, the current in the reactor can be expressed with
Vs (t) = V sin wt
From the basics Kirchhoff’s voltage equation can be
modulated as,
as follows
2.2 Thyristor Switched Capacitor(TSC):
Fig.1. Thyristor Controlled Reactor(TCR)
The Thyristor-Switched Capacitor (TSC). A singlephase thyristorswitched capacitor (TSC) is shown in
Figure 3. It consists of a capacitor, a bidirectional
thyristor valve, and a relatively small surge current
limiting reactor. This reactor is needed primarily to limit
the surge current in the thyristor valve under abnormal
operating conditions (e.g., control malfunction causing
capacitor switching at a "wrong time," when transient
free switching conditions are not satisfied); it may also
be used to avoid resonances with the ac system
impedance at particular frequencies. Under steady-state
conditions, when the thyristor valve is closed and the
TSC branch is connected to a sinusoidal ac voltage
source, v = V sin on, the current in the branch is given
by
The ant parallel thyristors pair act like a bidirectional
switch ,with thyristors valve T1 conducting in positive
half cycle and thyristors T2
conducting in negative half cycle of the supply voltage
.the firing angle of the thyristors is measured from the
zero crossing of the voltage
appearing across its terminal. the controllable range of
the TCR firing angle ,α,extends from 900 to 1800 .the
continuous sinusoidal current flow in the TCR but as α
range ,the current reduce to zero for a firing angle of
1800 and below 900 ,it introduce a dc current ,disturbing
the symmetrical operation of the two antiparallel valve
branches.
It consists of a fixed (usually air-core) reactor of
inductance L, and a bidirectional thyristor valve (or
switch) sw. A thyristor valve can be brought into
conduction by simultaneous application of a gate pulse
to all thyristors of the same polarity. The valve will
automatically block immediately after the ac current
crosses zero, unless the gate signal is re-applied. The
current in the reactor can be controlled from maximum
(thyristor valve closed) to zero (thyristor valve open) by
the method of firing delay angle control This method of
current control is illustrated separately for the positive
and negative current half-cycles in Fig1, where the
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International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE)
ISSN: 0976-1353 Volume 14 Issue 2 –APRIL 2015.
Fig.2.Thyristor Switched Capcitor (TSC)
IV. Observations:
SVC can be operated in two different modes:

In voltage regulation mode (the voltage is
regulated within limits as explained below).

In var control mode (the SVC susceptance
is kept constant)
III. STRUCTURE
MODEL:
OF
THE
SIMULATION
The work presented in this paper is simulated by using
the SIMULINK modeling. Primarily the parameters of
the transmission line are formulated and then the
modeling of transmission line is carried out using the
software and here Pi-section transmission line is
preferred for the analysis. After modeling, the voltage
regulation, Real and Reactive Power, Total Harmonic
Distortion (THD),Efficiency of the transmission line is
plotted under the steady state condition of the line.
Then modeling of SVC is done by setting the firing
angle and the values of the capacitor and inductor
employed in modeling as shown in Figure 5, after this
the above said parameters of the line with SVC is
tabulated as shown below. Then finally the Voltage
stability, Real and Reactive Power, THD with and
without SVC is analyzed and the changes in the system
are observed.
3.1 Parameters of Transmission line, Source and
the Load:
392
50
45
40
35
30
25
20
15
10
5
0
Without SVC
With SVC
Fig.3.Transmission Line With SVC
International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE)
ISSN: 0976-1353 Volume 14 Issue 2 –APRIL 2015.
Source
Line Voltage
440KV, 50Hz
Stargrounded
3 phase short
circuit
level
base
=MVA 5000
Base
Voltage=440
KV
X/R
ratio=
7.0
Load
Star-grounded
Line
Pi –model (π)
V=440KV
Active
power=P=200MW
Resistance=R=0.10Ω
/km
Inductance=L=0.95m
H/km
Reactive
Power=Q=150MVAr
Capacitance=C=4.8µ
F/km
Line length=Varied
from 400-1500km
Fig.4. Voltage Regulation With Varying Line
Length
Flow Studies”, IEEE Transactions on Power Systems, Vol. 15(1),
pp.129-136, 2000.
[4] L. Cai, “ Robust Coordinated Control of FACTS Devices in Large
Power Systems”, a PhD Thesis, University of Duisburg, Germany,
published by Logos Verlag Berlin, 2004.
[5] T. Orfanogianni and R. Bacher. “Steady-state optimization in
power systems with series FACTS devices”, IEEE Transactions on
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[6] B.H. Kim and R. Baldick. “A comparison of distributed optimal
power flow algorithms”, IEEE Transactions on Power Systems, Vol.
15(2), pp. 599–604, 2000.
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terms and dentitions for flexible AC transmission system (FACTS)”,
IEEE Transactions on Power Delivery, 12(4):1848, 1997.
[8] Mark Ndubuka, “Voltage Stability Improvement using Static Var
Compensator in Power Systems”, Leonardo Journal of Sciences Issue
14, pp. 167-172, January-June 2009.
[9] Thukaram, Dhadbanjan, H. P. Khincha, and B. Ravikumar,
“Harmonic minimization in the operation of static VAR compensators
for unbalanced reactive power compensation”, International
Conference on Power System Technology, Vol.1, and Page: 328 - 334,
2004.
[10] Lockley, Bill, Philpott, Gerard “Static VAr compensators-a
solution to the big motor/weak system problem”, IEEE Industry
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[11] E.R. Chaparro, and M.L. Sosa,“Coordinated tuning of a set of
Static Var Compensators using Evolutionary Algorithms”, IEEE
Trondheim Power Tech, pp. 1 – 6, 2011.
CONCLUSIONS:
Finally we can conclude that the SVC results in the
voltage stability of the transmission line and higher
reactive power compensation in the line reactance.
Power quality is improved due to voltage stability, Real
and Reactive Power and THD analysis achieved in the
line. Further these studies can be extended to analyze the
power quality issues for different firing angles, fault
study analysis of transmission line and different
transient and steady state analysis for variable loads. For
varying load conditions and transients, ac transmission
network requires dynamic reactive power control.
Similarly, further there is a platform for employing the
other FACTS devices such as TCSC, STATCOM,
SSSC,UPFC, UPQC for enhancing the voltage stability
of the transmission line and other power quality related
issues under steady state analysis and transient analysis
of the line.
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[3] E. Acha, H. Ambriz Perez, Fuerte Esquivel, “Advanced SVC
Models for Newton-Raphson Load Flow and Newton Optimal Power
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