International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 2 - Apr 2014
Performance Evaluation of Flexible AC Transmission and Simulation of
TCSC Using MATLAB/SIMULINK
Shashikumar R, Nagarathna M C , Siddalinga.S.Nuchhi
P.G. Scholar, Department of Electrical and Electronics Engineering, S.D.M College of Engineering and Technology, Dharwad580002, Karnataka, India
Abstract - The development of transmission systems follows
closely the increasing demand on electrical energy. 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, Flexible AC
Transmission System (FACTS) uses the thyristor controlled
devices and optimally utilizes the existing power network.
FACTS devices play 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. An
attempt is made in this paper for studying the aspects of FACTS,
and Simulation of TCSC, using SIMULINK for studying voltage
regulation, fault studies.
Keywords: Flexible AC Transmission Systems ,TCSC, Voltage
Stability
I. INTRODUCTION
In recent years, power demand has increased substantially
while the expansion of power generation and transmission has
been severely limited due to limited resources and
environmental restrictions. As a consequence, some
transmission lines are heavily loaded and the power system
stability becomes a power transfer-limiting factor. Flexible
AC transmission systems (FACTS) controllers have been
mainly used for solving various power system steady state
control problems. However, recent studies reveal that FACTS
controllers could be employed to enhance power system
stability in addition to their main function of power flow
control [3]. AC transmission lines are dominantly reactive
networks, characterized by their per-mile series inductance
and shunt capacitance. Thus, load and load power factor
changes alter the voltage profile along the transmission lines
and can cause large amplitude variations in the receiving end
voltage. Most of loads are not tolerant to voltage variation.
Under voltage causes degradation in the performance of the
loads and overvoltage causes magnetic saturation and resultant
harmonic generation, as well as equipment failure due to
insulation breakdown. 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 [4]. It becomes necessary to explore
new ways of maximizing power transfer in existing
transmission facilities, while at the same time maintaining the
acceptable levels of the network reliability and stability. On
the other hand, the fast development of power electronic
technology has made FACTS (flexible AC Transmission
system), introduced in 1974, are promising solution of future
power system. FACTS controllers such as Static Synchronous
Compensator (STATCOM), Static VAR Compensator (SVC),
Thyristor Controlled Series Compensator (TCSC), Static
ISSN: 2231-5381
Synchronous Series Compensator (SSSC) and Unified Power
Flow controller (UPFC) are able to change the network
parameters in a fast and effective way in order to achieve
better system performance. [9][11] The technical and
economical benefits of these technologies represent an
alternative to the application in AC systems. Deregulation in
the power industry and opening of the market for delivery of
cheaper energy to the customers is creating additional
requirements for the operation of power systems.
HVDC and FACTS offer major advantages in meeting these
requirements.[5] However, widespread adoption of this
technology has been hampered by high costs and reliability
concerns. The concept of distributed FACTS devices, as an
alternative approach to realizing cost-effective power flow
control, has been proposed. [4]Increasing number of FACTS
devices have been be installed to reinforce the existing grid
and build the envisioned “Smartness” into the grid through
controls and optimization. However, it has been noticed that
adverse interactions among multiple FACTS controllers may
occur when they are not properly coordinated with each other
and other slowly acting system equipment.[15]
II. FACTS CONCEPT
The recent development of power electronics introduces
the use of Flexible ac transmission system (FACTS)
controllers in power system [16]. Flexible AC Transmission
Systems (FACTS) is a concept proposed by Hingorani that
involves the application of high power electronic controllers in
AC transmission networks which enable fast and reliable
control of power flows and voltages. FACTS technology is
collection of high power electronic controllers, which can be
applied individually or in coordination with others to control
one or more of the interrelated system parameters. The
thyristor or high-power transistor is the basic element for a
variety of high-power electronic Controllers. FACTS
technology provides the opportunity to [4] [12],
 Increase loading capacity of transmission lines.
 Prevent blackouts.
 Improve generation productivity.
 Reduce circulating reactive power.
 Improves system stability limit.
 Reduce voltage flicker.
 Reduce system damping and oscillations.
 Control power flow so that it flows through the
designated routes.
 Congestion management
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International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 2 - Apr 2014
The conventional control devices like synchronous condenser,
saturated reactor, thyristor controlled reactor, fixed capacitor
thyristor controlled reactor, thyristor switched capacitor
having less system stability limit, less enhancement of system
damping, less voltage flicker control when compared to
emerging facts devices like TCSC, STATCOM and UPFC
[13][5]. This paper investigates the improvement of system
stability with various emerging FACTS devices and their
comparisons. [6] - [7]
The main aim of this paper is to analyze the voltage
stability of the power system network taking into account the
design of TCSC controller for stability enhancement of the
power system, by considering the interactions among the
different control levels. Primary transmission Pi-section model
is developed using the Simulink model by considering the
design parameters of the line and the steady state analysis for
the voltage regulation in the system is carried out by varying
the transmission line length. Then the TCSC controller is
designed with various parameters for the set Firing angle and
is connected to the transmission line, the analysis with TCSC
is done and the voltage regulation different line length is
tabulated. Finally the percentage voltage regulation for the
system with and without TCSC is tabulated and analyzed.This
paper is structured as follows: Section 2 briefly describes
about the TCSC controller, as well as the controller model
used in this paper. In Section 3, the proposed test system
model of the transmission line and the TCSC model is
illustrated. Section 4 the analysis and results are summarized,
the main contributions of this paper is analyzed.
III. TCSC MODELING AND BASIC CONTROL
SCHEME
The basic Thyristor-Controlled Series Capacitor
scheme, proposed in 1986 by Vithayathil with others as a
method of "rapid adjustment of network impedance," The
basic conceptual TCSC module comprises a fixed series
capacitor (FC), in parallel with a thyristor-controlled reactor
(TCR)as shown in Figure 2. The TCR is formed by a reactor
in series with a bi-directional thyristor valve that is fired with
a phase angle ranging between 90º and 180º with respect to the
capacitor voltage. A TCSC is a series-controlled capacitive
reactance that can provide continuous control of power on the
ac line over a wide range. The principle of variable-series
compensation is simply to increase the fundamental-frequency
voltage across an fixed capacitor in a series compensated line
through appropriate variation of the firing angle. This
enhanced voltage changes the effective value of the seriescapacitive reactance and control the reactive power [5] [10].
In a practical TCSC implementation, several such basic
compensators may be connected in series to obtain the desired
voltage rating and operating characteristics.
This arrangement is similar in structure to the TSSC
and, if the impedance of the reactor XL, is sufficiently smaller
than that of the capacitor Xc it can be operated in an on off
manner like the TSSC. However, the basic idea behind the
TCSC scheme is to provide a continuously variable capacitor
by means of partially canceling the effective compensating
capacitance by the TCR. The TCR at the fundamental system
frequency is a continuously variable reactive impedance,
controllable by delay angle a, the steady-state impedance of
the TCSC is that of a parallel LC circuit, consisting of a fixed
capacitive impedance Xc,and a variable inductive impedance
XL(α),[2]
XTCSC(α)=
Where,
XL(α)= XL
, XL≤ XL(α) ≤ ∞
XL=ώL and α is the delay angle measured from the crest of the
capacitor voltage (or, equivalently, the zero crossing of the
line current). The TCSC thus presents a tunable parallel LC
circuit to the line current that is Substantially a constant
alternating current source. As the impedance of the controlled
reactor, XL(α), is varied from its maximum (infinity) toward
its minimum, the TCSC increases its minimum capacitive
impedance, XTCSC min = Xc = 1/ώC, (and thereby the degree of
series capacitive compensation) until parallel resonance at Xc
= XL(α) is established and XTCSC max theoretically becomes
infinite. Decreasing XL(α) further, the impedance of the
TCSC, XTCSC(α) becomes inductive, reaching its minimum
value of XLXc/(XL - Xc) at α = 0, where the capacitor is in effect
bypassed by the TCR. The steady-state model of the TCSC
described is based on the characteristics of the TCR
established in an SVC environment, where the TCR is
supplied from a constant voltage source. This model is useful
to attain a basic understanding of the functional behavior of
the TCSC.
A.Working:
Assuming that the thyristor valve, SW, is initially open and the
prevailing line current i produces voltage VCO across the fixed
series compensating capacitor, as in Fig 2.
Fig. 2.Illustration of capacitor voltage reversal by TCR: (a) equivalent circuit
of the TCSC at the firing instant a, and (b) the resulting capacitor voltage and
related TCR current.
Fig1.Basic conceptual TCSC module
ISSN: 2231-5381
Suppose that the TCR is to be turned on at α
measured from the negative peak of the capacitor voltage. As
seen, at this instant of turn-on, the capacitor voltage is
negative and the line current is positive, thus charging the
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International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 2 - Apr 2014
capacitor in the positive direction. During this positive halfcycle of TCR operation, the thyristor valve acts as an ideal
switch. Closing the switch at α, in series with a diode of
Load
Star-grounded
Line
Pi –model (π)
V=440KV
Active
power=P=200MW
Resistance=R=0.14Ω/km
Inductance=L=0.1046mH/k
m
PQ
V
I
Active & Reactive
Power
powergui
PQ
Active & Reactive
Power1
Power
+v
-
Vs
+
- v
A1
A2
Current
Vs1
a
A
B
A
a
B
b
TCSC
i
+ -
Is
C
C
Three-Phase Source
Pi Section Line
A1
Pi Section Line1
a
c
Three-Phase
V-I Measurement
A2
TCSC1
Pi Section Line2
A
a
+ i
-
B
b
Is1
C
c
Voltage
Three-Phase
V-I Measurement1
A1
A
B
C
Source
Line Voltage
440KV, 50Hz
Star-grounded
3 phase short
circuit
level base
=MVA 5000
Base
Voltage=440
KV
X/R ratio= 7.0
V
I
Discrete,
Ts = 5e-005 s.
A2
Three-Phase
Parallel RLC Load
a
Reactive
Power=Q=150MV
Ar
Capacitance=C=4.8µF/km
TCSC2
Fig. 3.SIMULINK model of TCSC connected to transmission line
Line length=Varied from
400-1500km
appropriate polarity to stop the conduction as the current
crosses zero, as shown in Fig 3. At this instant of closing
switch, SW, results in-(i) at the line current, being a constant
current source, continues to charge the capacitor and (ii) the
charge of the capacitor will be reversed during the resonant
half-cycle of the LC circuit formed by the switch closing.
(This second event assumes, as stipulated, that XL< XC) The
resonant charge reversal produces a dc offset for the next
(positive) half-cycle of the capacitor voltage, as in Fig 3.In the
negative half-cycle, this de offset can be reversed by
maintaining the same α. Hence a voltage waveform
symmetrical to the zero axis can be produced, as in Fig. 3,
where the relevant current and voltage waveforms of the
TCSC operated in the capacitive region are shown. Similar
waveforms are shown for the inductive operating range, where
the overall impedance of the TCSC is inductive.[2]. The
reversal of the capacitor voltage is clearly the key to the
control of the TCSC. The time duration of the voltage reversal
is dependent primarily on XL/XC ratio, but also on the
magnitude of the line current. If XL < < XC, then the reversal is
almost instantaneous, and the periodic voltage reversal
produces a square wave across the capacitor that is added to
the sine wave produced by the line current.
IV. Simulation Results
Fig.4.Voltage Regulation for the Varying line length
100
Sending End
Real Power
Without TCSC
50
0
400 600 800 100012001400
Fig.5.Sending End and Receiving End Real Power(MW)
B.Details of the Simulation Model
ISSN: 2231-5381
5
0
-5
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
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 Pisection transmission line is preferred. After modeling the
voltage regulation of the transmission line is tabulated under
the steady state condition of line. Then modeling of TCSC 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 voltage regulation of the line with TCSC is tabulated as
shown below. Then finally the Voltage stability with and
without TCSC is analyze and the changes in the system are
observed.
Sending End
Reactive
PowerWithout
TCSC
Sending End
Reactive
PowerWith
TCSC
-10
-15
Fig.6.Sending End and Receiving End Reactive Power (MVAr)
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International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 2 - Apr 2014
V FAULT ANALYSIS
5000
4000
3000
2000
1000
0
Is(AB)
Is(BC)
Is(CA)
Isw(AB)
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 SVC,
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.
Isw(BC)
REFERENCES
Fig.7.Fault Current at the Sending End
600
500
Ir(AB)
400
Ir(BC)
300
Ir(CA)
200
Irw(AB)
100
Irw(BC)
0
Irw(CA)
Fig.8.Fault Current at the Receiving End
Fig.9.Waveforms for Fault Current
Thus, the conclusions of this simulation study indicate that
the voltage regulation is improved and also balancing of
reactive power can be achieved. Damping of active power
oscillations and rapid dynamic response, hence there is
improved voltage stability in the transmission line.
V CONCLUSIONS
Finally we can conclude that the TCSC 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 achieved in the line. Fault
analysis is also done for the system with and without TCSC.
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
ISSN: 2231-5381
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