International Journal of Research in Electrical & Electronics Engineering

Volume 1, Issue 2, October-December, 2013, pp. 25-33

© IASTER 2013, www.iaster.com

Analysis and Enhancement of Voltage Stability Using Shunt

Controlled FACTs Controller
1
Kiran Kumar Kuthadi, 2K. Silpa Devi
1
HOD& Assoc. Professor, Dept. of EEE, SVIST, Tiruvuru, AP
2
ASE, TCS, Hyderabad, Andhra Pradesh, India
ABSTRACT
A critical factor effecting power transmission systems today is power flow control. The increment of
load variation in a power transmission system can lead to potential failure on the entire system as the
system has to work under a Stressed condition. Thus, the Flexible AC Transmission Systems (FACTS)
are integrated in power system to control the power flow in specific lines and improve the security of
transmission line. This paper presents an optimal placement of SVC and STATCOM to determine SVC
and STATCOM 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 & STATCOM is placed based on FVSI. The results have
been obtained on IEEE 5 bus and IEEE 14bus test system. Test result shows that both SVC and
STATCOM can determine optimal placement.

Keywords: Flexible AC Transmission Systems (FACTS), Static VAR compensator (SVC), Static
Synchronous Compensator (STATCOM), Fast Voltage Stability Index (FVSI).

1.INTRODUCTION
Nowadays, the power transmission systems have been changed a lot. The voltage deviation due to load
variation and power transfer limitation were observed due to reactive power unbalances has drawn
attention to better utilize the existing transmission line. It also causes a higher Impact on power system
security and reliability in the world. Hence, the Electrical energy demand increases continuously from
time to time. This increase should be monitored or observed because few problems could appear with
the power flows through the existing electric transmission networks. If this situation fails to be
controlled, some lines located on the particular paths might become overloaded [1].

The Flexible AC transmission systems (FACTS) initiative was originally launched to solve the
emerging problems in the late 1980s due to restrictions on the transmission line construction and to
facilitate the growing power export/import and wheeling transactions among the utilities. FACTS
devices can enhance transmission system control and increase line loading in some cases all the way
up to thermal limits thereby without compromising reliability. These devices can be an alternative to
reduce the flows in heavily loaded lines, resulting in increased load ability, low system loss, improved
stability of the network, reduced cost of production and fulfilled contracture requirement by
controlling the power flows in the network, reduce cost of production and fulfilled contracture
requirement by controlling the power flows in the network. These capabilities allow transmission
system owners and operators to maximize asset utilization and execute additional bulk transfer with
immediate bottom-line benefits. FACTS devices provide new control facilities, both in steady state
power control and dynamic stability control [2].
International Journal of Research in Electrical & Electronics Engineering
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FACTS devices include static var compensator (SVC), thyristor controlled series compensator
(TCSC), unified power flow controller (UPFC) etc. SVC and STATCOM are connected in shunt with
the system to improve voltage profile by injecting or absorbing the reactive power [3, 4].

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 STATCOM 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 STATCOM 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. 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 [5].

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.
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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.

ii. Static Compensator (STATCOM)

The STATCOM consists of one VSC and its associated shunt-connected transformer. It is the static
counterpart of the rotating synchronous condenser but it generates or absorbs reactive power at a faster
rate because no moving parts are involved. In principle, it performs the same voltage regulation
function as the SVC but in a more robust manner because, unlike the SVC, its operation is not
impaired by the presence of low voltages as show below Fig.2 and Fig. 3

Fig. 2 Static compensator (STATCOM) system: voltage source converter (VSC) connected
to the AC network via a shunt-connected transformer

Fig. 3 Static compensator (STATCOM) system: shunt solid-state voltage source

3. FAST 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 having , generator
buses , and the load buses . The transmission system can be
represented by using a hybrid representation, by the following set of equations
International Journal of Research in Electrical & Electronics Engineering
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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,

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 STATCOM 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 STATCOM

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 STATCOM & SVC

Voltage stability indices are calculated for the IEEE 5 bus system without any FACTS devices as
shown in Fig. 3.
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Fig. 4 IEEE 5 Bus Test System with STATCOM

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 STATCOM to improve
power system security/stability. The modified original networks to include STATCOM as shown in
Fig. 4.

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

Name of FVSI Before FVSI After

the Bus STATCOM STATCOM
Lake 0.0299 0.0298
Main 0.0304 0.0286
Elm 0.0328 0.0099

Table 2: Analysis of Voltage magnitudes, Phase Angles for IEEE 5-bus

test system with & without STATCOM
Name Before Placement After Placement of
of the of STATCOM STATCOM
Bus VM VA (deg) VM(p.u) VA(deg)
(p.u)
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 3: Analysis of Sending, Receiving Active & Reactive Power for IEEE 5-Bus test system
with STATCOM
Branch Sending Active & Receiving Active &
Reactive Power Reactive Power
MW Mvar MW Mvar
1-2 89.4993 73.9781 86.9023 72.887
1-3 41.7921 14.4976 40.3353 15.399
2-3 24.3510 05.4332 23.9881 2.5512
2-4 27.6011 05.4789 27.1367 2.9076
2-5 54.9503 17.6303 53.6384 18.565
3-4 19.3235 02.1518 19.2854 0.2984
5-4 06.4221 08.2060 6.3616 3.4321
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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.

Fig. 5 IEEE 5 Bus Test System with SVC

Table 4: FVSI Before & After Placement of SVC

Name of FVSI Before FVSI After
the 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 Before Placement of After Placement of
of the SVC SVC
Bus 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
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4.2 IEEE 14-Bus Test System

i. Location of STATCOM
By considering the Fast Voltage stability index (FLj) value, it is observed that 14-bus is more sensitive
towards system security. Therefore 14-Bus is more suitable location for STATCOM to improve power
system security/stability and improvement of voltage stability as shown in Table 7 and Table 8.
Table 7: Analysis Voltage magnitudes, Phase Angles for IEEE 14-bus
test system without and with STATCOM
Name of Before Placement of After Placement of
the Bus STATCOM STATCOM
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 8: Analysis of Sending, Receiving Active & Reactive Power for IEEE 14 Bus
test system with STATCOM
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
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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.
Table 9: Analysis of Voltage magnitudes, Phase Angles for IEEE 14-bus
test system without and with SVC
Name Before Placement of After Placement of
of the SVC SVC
Bus 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 STATCOM
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 STATCOM were to maintain the voltage profile, minimize the voltage deviations and to
reduce the power losses using FVSI. Simulations performed on the test system shows that the
optimally placed SVC and STATCOM maintains the voltage profile, minimizes the deviations and
also reduces the real and reactive power losses.

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