kiran Kumar Kuthadi et al.

/ International Journal of Engineering Science and Technology (IJEST)

Optimal Location and Parameter Settings of

FACT’s Devices for Enhancing Power
System Stability and Minimization of
Power Losses
1
KIRAN KUMAR KUTHADI
Head of the Department
Electrical & Electronics Engineering
Sree Vahini Institute of Science & Technology, TIRUVURU, Krishna Dist, Andhra Pradesh
Email.id: kiran9949610070@gmail.com
2
M. SURESH BABU
Asst. Professor, Dept. of EEE
V.R.S & Y.R.N College of Engineering & Technology, CHIRALA, Prakasam Dist, Andhra Pradesh.
3
NAGARAJU TELLA
Asst. Professor, Dept. of EEE
Sree Vahini Institute of Science & Technology, TIRUVURU, Krishna Dist, Andhra Pradesh.

ABSTRACT: The loss minimization is a major role in Power System (PS) research. Transmission line losses in a
Power System can be reduced by Var compensation. After the establishment of power markets with transmission
open access, the significance and use of Flexible AC Transmission Systems (FACTS) devices for manipulating
line power flows to relieve congestion and maximize the overall grid operation have been increased. Proper
placement of Static VAR compensator (SVC) and Thyristor Controlled Series compensator (TCSC) reduces
transmission losses, increases the available capacity, and improves the voltage profile. This paper presents an
optimal placement of SVC and TCSC to determine SVC and TCSC locations and control parameters for
minimization of transmission loss. Optimal location methods utilize the sensitivity of total real power
transmission loss with respect to the control parameters of devices. The location of SVC & TCSC is placed based
on VSI. The results have been obtained on IEEE 5bus and IEEE 14bus test system. Test result shows that both
SVC and TCSC can determine optimal placement.
Index Terms: Flexible AC Transmission Systems (FACTS), Static VAR compensator (SVC), Thyristor
Controlled Series compensator (TCSC), Voltage Stability Index (VSI).

1. INTRODUCTION
Most of the large power system blackouts, which occurred worldwide over the last twenty years, which are caused
by heavily stressed system with large amount of real and reactive power demand and low voltage condition. When
the voltages at power system buses are low, the losses will also to be increased. This study is devoted to develop a
technique for improving the voltage and minimizing the losses and hence eliminate voltage instability in a power
system. Application of FACTS devices are currently pursued very intensively to achieve better control over the
transmission lines for manipulating power flows. There are several kinds of FACTS devices. Thyristor-Controlled
Series Capacitors (TCSC), Thyristor Controlled Phase Shifting Transformer (TCPST) and Static Var
Compensator (SVC) can exert a voltage in series with the line and, therefore, can control the active power through
a transmission line. The optimal operation of the power system networks have been based on economic criterion.
Now other criterion such as: improving voltage profile, minimizing power loss of transmission line, and etc. have
been concerned. An optimal power flow program (OPF) has been solved an optimization problem where the
objective function, equality and inequality constraints are nonlinear equation [1]. The Flexible AC Transmission
System (FACTS) have been considered to maximize the use of existing transmission facilities. In this paper
FACTS devices have been considered as additional control variables in power flow. Two of FACTS devices

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consisting of static var compensator (SVC) and thyristor controlled series compensator (TCSC) have been used in
this paper. Minimization of transmission loss is solved by using the nonlinear interior point methods [2] to finding
values of SVC and TCSC along with other control parameter such as transformer tap that was present in [3]. Due
to high cost of SVC and TCSC, it is important to decide their optimal placement.
This paper presents the method of the optimal location utilizes the sensitivity of total real power transmission
loss with respect to the control parameters of devices, the new equation of SVC is the sum of reactive power flow
that has relationship with bus and the new equation of TCSC is sum of real power loss that has relationship with
transmission line. The IEEE standard tested power system has been considered as tested system to investigate the
effect of considering TCSC and SVC on power loss minimization and system stability.
2. MATHEMATICAL MODEL OF FACT’S

i. Static VAR compensator (SVC)

The SVC is taken to be a continuous, variable susceptance, which is adjusted in order to achieve a
specified voltage magnitude while satisfying constraint conditions. SVC total susceptance model represents a
changing susceptance. represents the fundamental frequency equivalent susceptance of all shunt modules
making up the SVC. This model is an improved version of SVC models [2]. SVC’s normally include a
combination of mechanically controlled and thyristor controlled shunt capacitors and reactors. The most popular
configuration for continuously controlled SVC’s is the combination of either fix capacitor and thyristor controlled
reactor [3].

Fig. 1 Basic Structure of SVC

As far as steady state analysis is concerned, both configurations can modeled along similar lines, The
SVC structure shown in Fig. 1 is used to derive a SVC model that considers the Thyristor Controlled Reactor
(TCR) firing angle as state variable. This is a new and more advanced SVC representation than those currently
available. The SVC is treated as a generator behind an inductive reactance when the SVC is operating within the
limits. The reactance represents the SVC voltage regulation characteristic, i.e., SVC’s slope, [4]. The reason
for including the SVC voltage current slope in power flow studies is compelling. The slope can be represented by
connecting the SVC models to an auxiliary bus coupled to the high voltage bus by an inductive reactance
consisting of the transformer reactance and the SVC slope, in per unit (p.u) on the SVC base. A simpler
representation assumes that the SVC slope, accounting for voltage regulation is zero. This assumption may be
acceptable as long as the SVC is operating within the limits, but may lead to gross errors if the SVC is operating
close to its reactive limits.
The linearized equation of the SVC is given by the following Eqns. (i) and (ii) where the total
susceptance is taken to be the state variable.

0 0
0
at the end of iteration i, the variable shunt susceptance up dated according to the Eqn. (ii) given below

In this paper, the SVC Susceptance model is used for incorporation into an existing power flow
algorithm. Here, the SVC state variables are incorporated inside the Jacobian and mismatch equations, leading to
very robust iterative solutions.

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ii. Thyristor Controlled Series compensator (TCSC)

The effect of TCSC on network can be seen as a controllable reactance inserted in the related
transmission line. The model of the network with TCSC is show in Fig. 2 [6].

Fig. 2 A Model of TCSC

The TCSC consist of a capacitor bank and a thyristor controlled inductive branch connected in parallel
and series connected to the transmission line. The equivalent reactance of TCR, XLeq, at fundamental
frequency, is show in Eqn (iii). The controllable reactance, XTCSC, is directly used as the control variable that
can be determined by

2 sin 2
The power flow equation of the branch can be derived as follows
cos sin

sin cos
Where

3. VOLTAGE STABILITY INDEX

Voltage stability is becoming an increasing source of concern in secure operating of present-day power systems.
The problem of voltage instability is mainly considered as the inability of the network to meet the load demand
imposed in terms of inadequate reactive power support or active power transmission capability or both. It is
mainly concerned with the analysis and the enhancement of steady state voltage stability based on L-index.

Consider an -bus system having1, 2, 3, … , generator buses , and 1, 2, … , the load buses
. The transmission system can be represented by using a hybrid representation, by the following set of
equations

It can be seen that when a load bus approaches a steady state voltage collapse situation, the index
approaches the numerical value 1.0. Hence for an overall system stability condition, the index evaluated at any of
the buses must be less than unity. Thus the index value gives an indication of how far the system is from voltage
collapse. The indices for a given load condition are computed for all load buses. The equation for the
index for node can be written as,

| | | |
1 1

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| |
1

cos

sin

It can be seen that when a load bus approaches a steady state voltage collapse situation, the index
approaches the numerical value 1.0. Hence for an overall system voltage stability condition, the index evaluated at
any of the buses must be less than unity. Thus the index value gives an indication of how far the system is from
voltage collapse.

4. SIMULATION RESULTS

For the validation of the proposed FACT’s devices, both SVC and TCSC have been tested on the following
IEEE 5-Bus and IEEE 14-Bus test System. A MATLAB code for both techniques was developed for simulation
purpose.

4.1 IEEE 5-Bus Test System

i. Location of TCSC:
The solution for optimal location of FACT’s devices to minimize the installation cost of FACT’s devices
and overloads for IEEE 5-bus test system were obtained and discussed in this section.

Fig. 3 IEEE 5 Bus Test System without TCSC & SVC

Voltage stability indices are calculated for the IEEE 5 bus system without any FACTS devices as shown
in Fig. 3.

Fig. 4 IEEE 5 Bus Test System with TCSC

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By considering the Voltage stability index (Lj) value, it is observed that bus Elm is more sensitive towards
system security. Therefore bus Elm is more suitable location for TCSC to improve power system
security/stability. An additional node is termed as node Elmfa, is used to connect the TCSC. The modified original
networks to include a TCSC between nodes Elm and Elmfa as shown in Fig. 4.

Table 1: Voltage Stability Index (VSI) Before & After Placement of TCSC

Name of VSI Before TCSC VSI After TCSC

the Bus
Lake 0.0354 0.0279
Main 0.0358 0.0357
Elm 0.0391 0.0253
Elmfa ---- 0.0226

Table 2: Analysis of Voltage magnitudes, Phase Angles for

IEEE 5-bus test system with & without TCSC

Name of Before Placement of After Placement of

the Bus TCSC TCSC
VM (p.u) VA (deg) VM(p.u) VA(deg)
North 1.060 0.000 1.060 0.000
South 1.000 -2.061 1.000 -2.346
Lake 0.987 -4.637 0.998 -3.697
Main 0.984 -4.957 0.970 -6.544
Elm 0.972 -5.765 0.968 -6.530
Elmfa --- ---- 0.970 -6.534

Table 3: Analysis of Sending, Receiving Active & Reactive Power for

IEEE 5-Bus test system with TCSC

Branch Sending Active & Receiving Active &

Reactive Power Reactive Power
MW Mvar MW Mvar
1-2 89.4993 73.9459 87.0094 72.8471
1-3 41.6199 16.7018 40.1156 17.4362
2-3 24.2002 2.6449 23.8485 0.2510
2-4 27.3698 1.8850 26.9204 0.7055
2-5 55.4394 5.9579 54.1878 5.1170
3-4 18.9641 2.6872 18.9259 4.5173
6-5 5.8462 0.2227 5.8122 4.9135

ii. Location of SVC

The solution for optimal location of FACT’s devices to minimize the installation cost of FACT’s devices
and overloads for IEEE 5-bus test system were obtained and discussed in this section. By considering the Voltage
stability index (Lj) value, it is observed that bus Elm is more sensitive towards system security. Therefore bus Elm
is more suitable location for SVC to improve power system security/stability as shown in Fig. 5. After placement
of SVC voltage stability index is improved and system losses are reduced as shown in Table 4, Table 5 and Table
6.

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Fig. 5 IEEE 5 Bus Test System with SVC

Table 4: VSI Before & After Placement of SVC

Name of the VSI Before VSI After
Bus SVC SVC
Lake 0.0299 0.0298
Main 0.0304 0.0286
Elm 0.0328 0.0099

Table 5: Analysis of Voltage magnitudes, Phase Angles for

IEEE 5-bus test system without and with SVC

Name of Before Placement of After Placement of

the Bus SVC SVC
VM (p.u) VA (deg) VM(p.u) VA(deg)
North 1.060 0.000 1.060 0.000
South 1.000 -2.057 1.000 -2.063
Lake 0.993 -4.716 0.993 -4.713
Main 0.989 -5.034 0.991 -5.058
Elm 0.978 -5.849 1.000 -6.215

Table 6: Analysis of Sending, Receiving Active & Reactive Power for

IEEE 5-Bus test system with SVC

Branch Sending Active & Receiving Active &

Reactive Power Reactive Power
MW Mvar MW Mvar
1-2 89.38 73.97 86.90 72.89
1-3 41.79 14.49 40.34 15.40
2-3 24.35 05.43 23.99 02.55
2-4 27.60 05.47 27.14 02.91
2-5 54.95 17.63 53.64 18.57
3-4 19.32 02.15 19.29 00.30
4-5 06.42 08.20 06.36 03.43

4.2 IEEE 14-Bus Test System

i. Location of TCSC
By considering the Voltage stability index (Lj) value, it is observed that 14-bus is more sensitive towards
system security. Therefore 14-Bus is more suitable location for TCSC to improve power system security/stability
and improvement of voltage stability as shown in Table 7 and Table 8. An additional node is termed as 15-Bus, is
used to connect the TCSC.

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Table 7: Analysis Voltage magnitudes, Phase Angles for IEEE 14-bus test system without and with TCSC

Name of Before Placement of After Placement of

the Bus TCSC TCSC
VM (p.u) VA (deg) VM(p.u) VA(deg)
01 1.060 0.000 1.060 0.000
02 1.000 -4.551 1.000 -4.411
03 0.906 -12.809 1.000 -13.252
04 0.918 -9.872 0.982 -10.272
05 0.934 -8.261 0.990 -8.758
06 0.848 -16.041 1.000 -15.316
07 0.857 -14.320 0.976 -13.754
08 0.845 -14.320 1.000 -13.754
09 0.836 -16.888 0.959 -15.630
10 0.828 -17.199 0.958 -15.901
11 0.834 -16.831 0.975 -15.742
12 0.829 -17.390 0.982 -16.271
13 0.823 -17.506 0.975 -16.293
14 0.807 -18.785 0.946 -17.190
15 --- --- 0.947 -17.009

Table 8: Analysis of Sending, Receiving Active & Reactive Power for IEEE 14 Bus test system with TCSC

Branch Sending Active & Receiving Active &

Reactive Power Reactive Power
MW Mvar MW Mvar
1-2 157.80 59.63 152.86 47.35
2-3 74.84 12.86 72.14 22.03
2-4 55.19 6.04 53.40 9.62
1-5 76.52 18.74 73.51 8.90
2-5 41.13 7.04 40.14 8.37
3-4 22.06 19.04 22.65 19.23
4-5 60.67 0.77 61.18 0.22
5-6 44.88 1.28 44.88 6.46
4-7 27.83 3.91 27.83 2.20
7-8 0.00 13.54 0.00 13.88
4-9 15.80 4.93 15.80 3.35
7-9 27.83 15.74 27.83 14.56
9-10 4.78 0.92 4.77 0.94
6-11 7.92 8.96 7.78 8.67
6-12 7.94 3.20 7.85 3.01
6-13 17.82 9.96 17.55 9.41
9-14 9.35 0.49 9.22 0.23
10-11 4.23 6.74 4.28 6.87
12-13 1.75 1.41 1.74 1.40
13-14 5.78 5.02 5.68 4.80

ii. Location of SVC

The solution for optimal location of FACT’s devices to minimize the installation cost of FACT’s devices
and overloads for IEEE 14-bus test system were obtained and discussed in this section. By considering the
Voltage stability index (Lj) value, it is observed that 14-Bus is more sensitive towards system security. Therefore
14-Bus is more suitable location for SVC to improve power system security/stability and improve voltage stability
as show in Table 9 and Table 10.

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Table 9: Analysis of Voltage magnitudes, Phase Angles for IEEE 14-bus test system without and with SVC

Name of Before Placement of After Placement of

the Bus SVC SVC
VM (p.u) VA (deg) VM(p.u) VA(deg)
01 1.060 0.000 1.060 0.000
02 1.000 -4.551 1.000 -4.411
03 0.906 -12.809 1.000 -13.242
04 0.918 -9.872 0.985 -10.324
05 0.934 -8.261 0.992 -8.774
06 0.848 -16.041 1.000 -15.172
07 0.857 -14.320 0.984 -13.846
08 0.845 -14.320 1.000 -13.846
09 0.836 -16.888 0.976 -15.714
10 0.828 -17.199 0.972 -15.945
11 0.834 -16.831 0.982 -15.702
12 0.829 -17.390 0.989 -16.225
13 0.823 -17.506 0.987 -16.495
14 0.807 -18.785 1.000 -18.236

Table 10: Analysis of Sending, Receiving Active & Reactive Power for IEEE 14 Bus test system with SVC

Branch Sending Active & Receiving Active &

Reactive Power Reactive Power
MW Mvar MW Mvar
1-2 157.79 59.63 152.86 47.35
2-3 74.76 12.85 72.07 22.00
2-4 55.35 7.57 53.55 11.20
1-5 76.58 17.90 73.58 8.12
2-5 41.05 8.04 40.06 9.37
3-4 22.13 17.46 22.69 17.75
4-5 61.65 3.18 62.17 2.15
5-6 43.87 0.70 43.87 5.63
4-7 28.48 1.05 28.48 0.71
7-8 0.00 8.72 0.00 8.85
4-9 16.23 2.32 16.23 0.78
7-9 28.48 8.01 28.48 7.02
9-10 5.40 2.32 5.39 2.29
6-11 7.21 5.53 7.13 5.36
6-12 7.53 0.90 7.46 0.75
6-13 17.93 0.86 17.71 0.44
9-14 9.80 12.93 9.45 13.68
10-11 3.61 3.51 3.63 3.56
12-13 1.36 0.85 1.36 0.85
13-14 5.57 6.21 5.45 6.46

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5. CONCLUSION

In this paper, a new method for optimal placement and parameters settings of SVC and TCSC has been
proposed for improving voltage profile in a power system. The proposed approach has been implemented on IEEE
5-bus and IEEE 14-Bus system. The criteria for selection of optimal placement of SVC and TCSC were to
maintain the voltage profile, minimize the voltage deviations and to reduce the power losses using VSI.
Simulations performed on the test system shows that the optimally placed SVC and TCSC maintains the voltage
profile, minimizes the deviations and also reduces the real and reactive power losses.

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