Comparison of Shunt Facts Devices for the Improvement of Transient Stability of Two Machine Power System Using MATLAB Modelling

IJSRD - International Journal for Scientific Research & Development| Vol. 3, Issue 10, 2015 | ISSN (online): 2321-0613
All rights reserved by www.ijsrd.com 944
Comparison of Shunt Facts Devices for the Improvement of Transient
Stability of Two Machine Power System using MATLAB Modelling
Arti Devi Patel
Department of Electrical Engineering
Jabalpur Engineering College, Jabalpur, (MP) India
Abstract— This paper presents, the performance of
STATCOM placed at midpoint of the two machine power
system and compared with the performance of SVC. The
comparison of various results found for the different type of
faults (single line, double line & three phase fault) occur in
long transmission line, and their removal by using shunt
FACTS devices is analysed. Computer simulation results
under a severe disturbance condition (three phase fault) for
different fault clearing times, and different line lengths are
analyzed. Both controllers are implemented using
MATLAB/SIMULINK. Simulation results shows that the
STATCOM with conventional PI controller installed with
two machine three bus systems provides better damping
oscillation characteristics in rotor angle as compared to two
machine power system installed with SVC. The transient
stability of two machine system installed with STATCOM
has been improved considerably and post settling time of the
system after facing disturbance is also improved.
Key words: Transient stability; FACTS devices; SVC,
STATCOM; MATLAB/SIMULINK
I. INTRODUCTION
Transient stability is important from the point of view
maintaining system security that is the incidence of a fault
should not lead to tripping of generating unit due to loss of
synchronism and the possibility of a cascaded outage
leading to system black out. In recent years, power demand
has increased substantially while the expansion of power
generation and transmission has been severely limited [1]
due to limited resources and environmental restrictions.
Transient stability limit depends on the type of disturbance,
location and magnitude of disturbance, the type of fault and
its location in the system, the time required to clear the fault.
Recent development of power electronics introduces the use
of FACTS devices in power systems. FACTS devices are
capable of controlling the network condition in a very fast
manner and this unique feature of FACTS devices can be
exploited to improve the transient stability of a system.
Reactive power compensation is an important issue in
electrical power systems and shunt FACTS devices play an
important role in controlling the reactive power flow to the
power network and hence the system voltage fluctuations
and transient stability [2]. SVC and STATCOM are
members of FACTS family that are connected in shunt with
the system. Even though the primary purpose of shunt
FACTS devices is to support bus voltage by injecting (or
absorbing) reactive power, they are also capable of
improving the transient stability by increasing (decreasing)
the power transfer capability when the machine angle
increases (decreases), which is achieved by operating the
shunt FACTS devices in capacitive (inductive) mode [3].
Shunt FACTS devices give maximum benefit from
their stabilized voltage support when sited at the mid-point
of the transmission line [4]. It is observed that STATCOM
gives better results for transient stability as compared to
SVC.
A. Problem Statement:
The transient stability studies involve the determination of
whether or not synchronism is maintained after the machine
has been subjected to severe disturbance. This may be
sudden application of load, loss of generation, loss of large
load, or a fault on the system. In most disturbances,
oscillations are of such magnitude that linearization is not
permissible and the nonlinear swing equation must be
solved. The stability problem is concerned with the behavior
of the synchronous machines after they have been perturbed.
If the perturbation does not involve any net change in
power, the machines should return to their original state. If
an unbalance between the supply and demand is created by a
change in load, in generation, or in network conditions, a
new operating state is necessary. In any case all
interconnected synchronous machines should remain in
synchronism if the system is stable; i.e., they should all
remain operating in parallel and at the same speed. This
paper is organized as following the Introduction and
problem statement, Section II illustrates the Two-area Power
System Model. In section III presents brief details about
Shunt FACTS devices such as Static Var Compensator
(SVC), Static Synchronous Compensator (STATCOM).
Section IV presents the simulation model and result without
FACTS devices and with SVC, STATCOM individually
when a 3-ph fault occurred between bus bars B1 & B2.
Section V presents results of the proposed model.
II. DESIGN OF STUDY MODEL OF POWER SYSTEM
An extended power system can be dividing into a number of
load frequency control areas inter connected by means of
tie-lines. Without loss of generality we shall consider a two
area case connected by a single tie-line as illustrated in fig1.
The two machines are equipped with a hydraulic turbine and
governor (HTG), excitation system and power system
stabilizer (PSS). Both SVC and STATCOM used for this
model have the same rating of ±200 MVA and the reference
voltage is set to 1 pu for both SVC and STATCOM. A three
phase fault occurs at sending end bus at time t = 4.0s, for
0.1sec time duration. The original system is restored upon
the clearance of the fault.
Fig. 1: Two-Area Power System with FACTS Device.
The transient following a system perturbation is
oscillatory in nature, but if the system is stable, these

Comparison of Shunt Facts Devices for the Improvement of Transient Stability of Two Machine Power System using MATLAB Modelling
(IJSRD/Vol. 3/Issue 10/2015/211)
oscillations will be damped toward a new quiescent
condition. These oscillations however are reflected as
fluctuations in the power flow over the transmission lines. If
a certain line connecting the two groups of machines
undergoes excessive power fluctuations, it may be tripped
out by its protective equipment there by disconnecting the
two groups of machines. This problem is termed the stability
of the tie line, even though in reality it reflects the stability
of the two groups of the machines. The shunt converter is
able to generate or absorb controllable reactive power in
both operating modes (i.e., rectifier and inverter). The
independently controlled shunt reactive compensation can
be used to maintain the shunt converter terminal AC voltage
magnitude at a specified value.
III. SHUNT FACTS DEVICES
FACTS controllers may be based on thyristor devices with
no gate turn-off or power devices with gate turn-off
capability. FACTS controllers are used for the dynamic
control of voltage, impedance and phase angle of high
voltage AC transmission lines. The basic principles of the
following FACTS controllers, which are used in the two-
area power system under study, are discussed briefly [5].
A. Static Var Compensator (SVC)
Static var systems are applied by utilities in transmission
applications for several purposes. The primary purpose is
usually for rapid control of voltage at weak points in a
network. Installations may be at the midpoint of
transmission interconnections or at the line ends. Static Var
Compensators are shunt connected static generators /
absorbers whose outputs are varied so as to control voltage
of the electric power systems. In its simple form, SVC is
connected as Fixed Capacitor-Thyristor Controlled Reactor
(FC-TCR) configuration as shown in Fig. 2(a). The SVC is
connected to a coupling transformer that is connected
directly to the ac bus whose voltage is to be regulated. The
effective reactance of the FC-TCR is varied by firing angle
control of the anti-parallel thyristors. The firing angle can be
controlled through a PI (Proportional + Integral) controller
in such a way that the voltage of the bus, where the SVC is
connected, is maintained at the reference value.
Fig. 2: (a) SVC Fig. 2(b): STATCOM
B. Static Synchronous Compensator (STATCOM)
A STATCOM, controlled to regulate the terminal voltage,
can increase the transient stability by maintaining the
transmission voltage at the midpoint or some appropriate
intermediate point in face of the increased power flow
encountered immediately after fault clearing. However, the
transient stability can be increased further by temporarily
increasing the voltage above the regulation reference for the
duration of the first acceleration period of the machine. The
voltage increased above its nominal value will increase the
electric power transmitted and thus will increase also the
deceleration of the machine. This is illustrated in fig. 2(b),
where the P versus δ plots of a simple two-machine system
with different midpoint compensations represents the P
versus δ is shown [2, 6]. The plot marked P =2V2
sin(δ/2)/X
plot obtained with an ideal compensator holding the
midpoint voltage constant. The plots marked with
STATCOM and SVC represents these compensators with a
given rating insufficient to maintain constant midpoint
voltage over the total range of δ. Thus, the P versus δ plots
are identical to that of the ideal compensator up to a specific
δ (δ = δi) at which the SVC becomes a fixed capacitor and
the STATCOM a constant current source. In the interval
between δi and δ, the P versus δ plots are those which
correspond to a fixed midpoint capacitor and a constant
reactive current source. The continuations of these plots in
the δi to zero interval show the P versus δ characteristic of
the two-machine system with the maximum capacitive
admittance of the SVC and with the maximum capacitive
output current of the STATCOM. That is angles smaller
than δi the transmission line is overcompensated and for
angles greater, it is undercompensated. This
overcompensation capability of the compensator can be
exploited to enhance the transient stability by increasing the
var output to the maximum value after fault clearing.
IV. SIMULATION MODEL
A 1000 MW hydraulic generation plant1 is connected to a
load centre through a long 500 kV,720 km transmission line.
The load centre is modeled by a 5000 MW resistive load.
The load is fed by the remote 1000 MW plant and a local
hydraulic generation plant2 of 5000 MW. In order to
maintain system stability after faults, the transmission line is
shunt compensated at its centre by a 200-MVAR SVC, and
STATCOM respectively (Fig. 3, 4). In fig. 5 system is
shown without FACTS devices.
Fig. 3: Two Machine Power System Simulink Model with
SVC Controller

Fig. 4: Two Machine Power System Simulink Model with
STATCOM Controller.
Fig. 5: Two Machine Power System Simulink Model
without Shunt FACTS Controller.
A. Simulation Results with Different Type of Fault:
By using fault circuit breaker different type of fault is
created in the system. When phase A is selected single phase
fault occur. Same way phase A, B selected and double line
fault occur. By selecting phase, A, B, C, create three phase
fault. This is observed that without shunt FACTS devices
PSS is able to remove single line-to-ground faults, but in
three phase fault condition its failed. Positive sequence
voltage, line power, rotor angle difference, speeds, and
terminal voltage with three phase fault with respect to time
and without FACTS devices shown in fig.6.
Fig. 6: Three Phase Fault without FACTS Devices.
Fig. 7: Three Phase Fault with SVC
Fig. 8: Three Phase Fault with STATCOM
The system has a SVC/STATCOM installed at B2.
It is considered that a 3-phase symmetrical short circuit fault
of 0.1seconds occur at bus B1. Put the Multi band type PSS
in service by setting the command in PSS block equal to 2.
Open the SVC/STATCOM block menu and change the
mode of operation to voltage regulation. The system is
simulated in Matlab/Simulink environment and graphs of
SVC STATCOM are shown in fig-7 and fig-8. From the fig-
7 and 8, it is inferred that the oscillations in generator rotor
angle is decreased and settling time for the oscillations is
found to be 2.8 seconds by using STATCOM. Also,

terminal voltages profile has been improved after clearance
of fault installed with STATCOM. Hence, the transient
stability of two machine system installed with STATCOM
has been improved considerably and post settling time of the
system after facing disturbance is also improved. It is also
observed that both shunt devices responses are
approximately same at single line to ground fault and double
line fault, but for three phase fault STATCOM performance
is better. These results are shown in table-1
Single line Double line Three phase
Without FACTS 2.4 sec 3.6sec infinite
SVC 1.8sec 2.2sec 3.9sec
STATCOM 1.7sec 2.1sec 2.3sec
Table 1: Post Fault Settling Time with Different Type of
Faults of Two Area Power System
V. SIMULATION RESULTS WITH DIFFERENT LINE LENGTH
On placing the SVC/STATCOM in the transmission line at
the distance of L1=360km & L2=360km i.e. absolutely at
the midpoint of the transmission line, with three phase fault
we can get the stabilized waveform at fault clearing time
t=0.1 sec only. Shown in fig.7 and 8.
Next we place the STATCOM/SVC at the distance
L1=370km & L2=370km and observe the waveform as
shown in fig 9 and 10, respectively. From the waveforms we
can say that by placing STATCOM at this length system is
stable at 3.7 sec but in case of SVC system become unstable.
Fig. 9: STATCOM with Three Phase Fault at 740km Length
Fig. 10: SVC with Three Phase Fault at 740 Km Length
When we increase the line length L1=380km,
L2=380km and place the STATCOM in middle of the line
then the results are shown in fig11. At this length both
devices give unstable results. By observing table-2 we
conclude that STATCOM performance is better for longer
line length as compared to SVC.
Fig. 10: STATCOM with Three Phase Fault at 760 Km
Length.
Transmission line
length(km)
SVC
[Rotor angle
difference
(degree)], settling
time
STATCOM
[Rotor angle
difference (degree)],
settling time
L1=350,L2=350
110 , 2.3sec
stable
108, 2.2sec
stable
L1=360,L2=360 121, 3.7sec stable
112, 2.3sec
stable
L1=370,L2=370 1080, unstable 120, 3.7sec
L1=380,L2=380 1080, unstable 1080, unstable
Table 2: Comparison of SVC and STATCOM at Different
Line Length.
VI. CONCLUSION
In this paper dynamics of the power system is compared
with and without the presence of FACTS devices and Power
system stabilizers in the event of major disturbances. The
performance of one of the FACT device i.e. STATCOM for
transient stability enhancement is compared with the
performance of other FACT device i.e. SVC. Proposed
FACTS controllers were implemented in MATLAB/
SIMULINK. Simulation results indicate that the STATCOM
controller installed with two machine systems provides
better damping characteristics in rotor angle as compared to
two machine system installed with SVC. Also, the post
settling time of the two machine system installed with
STATCOM is found to be less i.e. near to 2.3sec than the
system with SVC 3.7 sec. Thus, transient stability
enhancement of the two machine system installed with
STATCOM is better than that installed with SVC.
REFERENCES
[1] P. Kundur, “Power System Stability and Control”,
EPRI Power System Engineering Series (Mc Graw-
Hill, New York, 1994).
[2] HINGORANI, N. G.-GYUGYI,L.Understanding
FACTS: Concepts and Technology of Flexible AC
Transmission System, IEEE PRESS, 2000.
[3] GYUGYI, L. : Power Electronics in Electric Utilities:
Static Var Compensators, Proceedings of IEEE 76 No.
4 (April 1988), 483–494.
[4] KAZERANI, M.-MARCEAU, R.-WOLANSKI, Z.-
GALIA- NA, F. D.-MCGILLS, D.-JOOS, G. Mid-
Point Siting of FACTS Devices in Transmission Lines,
IEEE Trans. on Power Delv. 12 No. 4 (Oct. 1997),
17171722.
[5] D. Murali, Dr.M. Rajaram, N. Reka “Comparison of
FACTS Devices for Power System Stability

Enhancement”, International Journal of Computer
Applications (0975–8887), Volume–No.4, October
2010.
[6] K.R. Padiyar, “Power System Dynamics – Stability
and Control”, 2nd edition, B.S. Publications, 2002.
[7] Kaur, T. and Kakran, S. (2012). Transient stability
Improvement of Long Transmission Line System by
Using SVC. International Journal of Advanced
Research in Electrical, Electronics and Instrumentation
Engineering. 1(4).
[8] Sharma, D., K., Ahmed, A., Saluja, R. &Parmar, R.
Voltage Stability in Power System Using STATCOM.
International Journal of Electronics and Computer
Science Engineering. 1(2): 198-208.

Comparison of Shunt Facts Devices for the Improvement of Transient Stability of Two Machine Power System Using MATLAB Modelling

More Related Content

What's hot (18)

Similar to Comparison of Shunt Facts Devices for the Improvement of Transient Stability of Two Machine Power System Using MATLAB Modelling (20)

More from IJSRD (20)

Recently uploaded (20)

Comparison of Shunt Facts Devices for the Improvement of Transient Stability of Two Machine Power System Using MATLAB Modelling