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Oct. 2014. Vol. 5. No. 05 ISSN2305-8269

International Journal of Engineering and Applied Sciences © 2012 - 2014 EAAS & ARF. All rights reserved www.eaas-journal.org

44

MODELING AND SIMULATION STUDY OF THE USE OF STATIC

VAR COMPENSATOR (SVC) FOR VOLTAGE CONTROL IN NIGERIA

TRANSMISSION NETWORK

Oyedoja, Kayode. Oyeniyi

Department of Technical Education, Emmanuel Alayande College of Education, Oyo,

Oyo state, Nigeria.

E-mail: [email protected]

ABSTRACT

Flexible AC Transmission System (FACTS) controllers, such as the Static Var Compensator (SVC), employ

latest technology power electronic switching devices in electric power transmission systems to control voltage

and power flow, and improve voltage regulation. There is increase in demand for electricity globally to feed the

technology driven economy. Given a profit-driven, deregulated electric power industry coupled with increased

load growth, the power transmission infrastructure is being stressed to its upper operating limits to achieve

maximum economic returns to both generation and transmissions system owners. In such an environment,

system stability problems such as inadequate voltage control and regulation must be resolved in the most cost-

effective manner to improve overall grid security and reliability.

Static Var Compensators are being increasingly applied in electric transmission systems to economically

improve voltage control and post-disturbance recovery voltages that can lead to system instability. An SVC

provides such system improvements and benefits by controlling shunt reactive power sources, both capacitive

and inductive, with state-of-the-art power electronic switching devices.

Keywords: Voltage Stability, PSAT, Simulink, SVC, Power Transmission.

1. INTRODUCTION

The electric power system has grown in size and

complexity with a huge number of

interconnections to meet the increase in the electric

power demand. Moreover, the role of long distance

and large power transmission lines become more

important. Due to this today’s changing electric

power systems create a growing need for

flexibility, reliability, fast response and accuracy in

the fields of electric power generation,

transmission, distribution and consumption. Static

Var Compensators (SVC) devices are used to

improve voltage and reactive power conditions in

AC systems. It also increases damping. The

effectiveness of this controller depends on its

optimal location and proper signal selection in the

power system network [1]. SVC has the ability to

improve stability and damping by dynamically

controlling it’s reactive power output.

2. REVIEW OF RELATED LITERATURE

Nowadays, voltage collapse, due to the voltage

instability, is a major problem in power system.

Research work is going on to find new ways of

minimizing voltage collapse by increasing voltage

stability (Transient stability, Steady state stability).

There are many analytical methods for determining

voltage stability of power system. In [2], finding of

optimal location of SVC and TCSC, saddle node

bifurcation analysis is applied and power flow is

used to evaluate the effect of FACTS devices on

system load ability. In [3], the ability of power

system, on how to control small disturbances, for

example:- change in load has been discussed. In

[4], power quality improvement on how FACTS

devices are used and how to improve power

system operation has been studied. In [5], the

effect of SVC and STATCOM on static voltage

stability margin enhancement was studied. In [6],

various types of FACTS controller and their

performance characteristics have been described.

In [7], simulation and comparison of various

FACTS devices (FC-TCR, CPFC) using PSPICE

software have been done. In [8], modeling and

simulation of SSSC multi machine system for

power system stability enhancement was studied.

How to improve steady state stability by placing

SVC at different places has been discussed in [9].

In [10], use of FACTS controllers for the

improvement of transient stability has been

studied. In [11], using MATLAB/SIMULINK

software simulation was done to demonstrate the

performance of the system for each of the FACTS

devices for example, FC-TCR, STATCOM, TCSC,

SSSC and UPFC in improving the power profile

and there by voltage stability of the same. In [12],

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Oct. 2014. Vol. 5. No. 05 ISSN2305-8269


45

using MATLAB/SIMULINK software

performance of shunt capacitor, FC-TCR and

STATCOM has been discussed. In [13], Modelling

and Simulation of various FACTS devices (FC-

TCR, STATCOM, TCSC and UPFC) have been

done using MATLAB/SIMULINK software. [14],

discuss how SVC has successfully been applied to

control dynamic performance of transmission

system and regulate the system voltage effectively.

In this paper modeling and simulation study of the

use of Static Var Compensator (SVC) for Voltage

Control in Nigeria Transmission Network have

been done using SIMPOWERSYSTEMS /PSAT

software.

3. STATIC VAR COMPENSATOR

The Static Var Compensator (SVC) is a device of

the Flexible AC Transmission Systems (FACTS)

family using power electronics to control power

flow on power grids. The SVC regulates voltage at

its terminal 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.

Figure 1. Single-line diagram of an SVC and

its control System

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

phase-controlled (Thyristor Controlled Reactor or

TCR)[15],[16],[17].

Figure shows a single-line diagram of a static var

compensator and its control system.

The control system consists of:

o A measurement system measuring the

positive-sequence voltage to be controlled

o A voltage regulator that uses the voltage

error (difference between the measured

voltage Vm and the reference voltage Vref)

to determine the SVC susceptance B needed

to keep the system voltage constant

o A distribution unit that determines the TSCs

(and eventually TSRs) that must be switched

in and out, and computes the firing angle α of

TCRs

o A synchronizing system and a pulse

generator that send appropriate pulses to the

thyristors.

3.1 SVC V-I Characteristics

The SVC can be operated in two different modes:

In voltage regulation mode (the voltage is

regulated within limits)

In var control mode (the SVC susceptance is

kept constant)

When the SVC is operated in voltage regulation

mode, it implements the following V-I

characteristics [18].

Figure 2. SVC V-I characteristics

As long as the SVC susceptance B stays within the

maximum and minimum susceptance values

imposed by the total reactive power of capacitor

banks (Bcmax) and reactor banks (Blmax), the

voltage is regulated at the reference voltage Vref.

However, a voltage drop is normally used (usually

between 1% and 4% at maximum reactive power

output). The V-I characteristic is described by the

following three equations:

V = Vref + Xs.I SVC is in regulation range

( )

V = Positive sequence voltage (p.u.)

I=Reactive current (p.u./Pbase)(I>0 indicaates

an inductive current).

3.2 MODELING OF SVC

A 300-Mvar Static Var Compensator (SVC)

regulates voltage on a 6000-MVA 735-kV system.

The SVC consists of a 735kV/16-kV 333-MV

coupling transformer, one 109-Mvar thyristor-

controlled reactor bank (TCR) and three 94-Mvar


Oct. 2014. Vol. 5. No. 05 ISSN2305-8269


46

thyristor-switched capacitor banks (TSC1, TSC2,

TSC3) connected on the secondary side of the

transformer. Switching the TSCs in and out allows

a discrete variation of the secondary reactive

power from zero to 282 Mvar capacitive (at 16 kV)

by steps of 94 Mvar, whereas phase control of the

TCR allows a continuous variation from zero to

109 Mvar inductive. Taking into account the

leakage reactance of the transformer (15%), the

SVC equivalent susceptance seen from the primary

side can be varied continuously from -1.04 pu/100

MVA (fully inductive) to +3.23 pu/100 Mvar

(fully capacitive). The SVC sends appropriate

pulses to the 24 thyristors (6 thyristors per three-

phase bank) in order to obtain the susceptance

required by the voltage regulator.

Figure 3. Detailed model of SVC in

SimPowerSystems/Simulink

4. SIMULATION RESULTS OF IEEE 9-

BUS SYSTEM

Figure 4: PSAT model of IEEE 9-bus test

system

Table 1. Network Visualisation of simulation results for IEEE 9-bus test system

Table 2. Network Visualisation of simulation

results for IEEE 9-bus test system

Figure 7. Fault response of IEEE 9-bus test

system without and with SVC

Without FACTS With SVC

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4.1 Simulation results of IEEE 14-bus System

Figure 5. PSAT model of IEEE 14-bus test

system

Figure 6. Fault response of IEEE 14-

bus test system without and

with SVC Table 3. Network Visualisation of simulation

results for IEEE 14-bus test system


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4.2 Simulation results of Nigerian 31-bus

330 kV network

Figure 9. Detailed model of Nigeria 31-

bus high voltage network in

PSAT (see larger figure in

appendix 1)


Oct. 2014. Vol. 5. No. 05 ISSN2305-8269


48

Figure 8. Fault response of Nigeria 31-bus

network without and with SVC

Table 4. Network visualization of

simulation results for Nigeria 31-bus network


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It can be seen from the network visualization

diagram that the presence of SVC smoothens the

distribution of flow in the network to achieve a

more balanced and uniform power flow.

5. SUMMARY

The aim of this paper is to show, through computer

modeling and simulation, that static var

compensator (SVC) can be used to control voltage

stability on Nigeria 31-bus 330 kV power

transmission network. Its objectives includes,

among other things, the modeling and simulation

study of the use of svc in the Nigeria 31-bus 330

kV power transmission network, using

mathematical simulation software. The modeling

and simulation study were carried out in Matlab

environment, using simpowersystems and PSAT.

Simpowersystems was used to study the steady

state and dynamic characteristics of a 330 MVAR

SVC, while PSAT was used to study the time

domain behavior of IEEE 9-bus and 14-bus test

systems under normal and faulty condition with

and without svc. Also PSAT was used to create a

model of Nigeria 31-bus 330 kV power

transmission network. Various simulation tests

were carried out on the model to study the time

domain response of the network to simulated faults

with and without SVC in place. The simulation

results show that the presence of SVC smoothes

the dynamic response of the system to faults. The

SVC, in its inductive role, also absorbs excess

power from the generating stations, thus overtime

the demand on the station settles to an optimum

level. Once this steady state is reached the SVC

regulates the network voltage by absorbing power

when voltage is high and generating power, in its

capacitive role, when voltage is low, thus maintain

stable voltage level and constant power towards

the distribution networks.

5.1 CONCLUSION

This paper has demonstrated that modern

transmission static var compensators can be

effectively applied in power transmission systems

to solve the problems of poor dynamic

performance and voltage regulation in Nigeria 31-

bus 330 kV transmission system. Transmission

SVCs and other FACTS controllers will continue

to be applied with more frequency as their benefits

make the network “flexible” and directed towards

an “open access” structure.

Since SVC is a proven FACTS controller, it is

likely that utilities will continue to use the SVC’s

ability to resolve voltage regulation and voltage

stability problems. In some cases, transmissions

SVC also provide an environmentally-friendly

alternative to the installation of costly and often

un-popular new transmission lines.


Oct. 2014. Vol. 5. No. 05 ISSN2305-8269


49

The model developed in this study offers

opportunity for more fine tuning and refinement to

reflect the accurate status of the Nigeria

transmission network.

Dynamic performance and voltage control analyses

will continue to be a very important process to

identify system problems and demonstrate the

effectiveness of possible solutions. Therefore,

continual improvements of system modeling and

device modeling will further ensure that proposed

solutions are received by upper management with

firm confidence.

References

1. Atef Aly El-Emary (1977), “Effect of

static VAR compensator upon

synchronizing Torque coefficient.”

Electric Machines and Power systems

25:pp. 371-387.

2. Ahadkazemi and BabakBadrezadeh

(1987), “Modeling and simulation of SVC

and TCSC to study their effects on

maximum loadabilitypoint”, EPRI

technical report EL-4365.

3. Abhijit Chakrabarti & sunitaHalder

(2006), “Power system analysis operation

and control”. Prentice Hall of India Pvt.

Limited, New Delhi.

4. M.P. Donsion, J.A. Guemes and J.M.

Rodriguez (2007), “Power Quality

Benefits of Utilizing FACTS Devices in

Electrical power system”, IEEE 2007,

pp 26-29.

5. Mehrdada Ahmadi Kamarposhti and

Mostafa Alinezhad (2008), “Comparison

of SVC and STATCOM in Static Voltage

stability margin Enhancement”. World

Academy of science, Engineering and

Technology, 50.

6. D. Murali, M. Rajaram and N. Reka,

(2010) “Comparison of FACTS Devices

for Power System Stability

Enhancement”, International Journal of

Computer Applications, volume 8-No4.

7. S. Sankar, S. Balaji and S. Arul (2010)

“Simulation and comparison of Various

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science and Technology, 2 (4), pp 538-

547.

8. S. Muthukrishnan and A. Nirmal Kumar

(2010) “Comparison of Simulation and

Experimental Results of UPFC used for

power quality improvement”.

International Journal of Computer and

Electrical Engineering, 2(3).

9. Bhavin. M. Patel (2011), “Enhancement

of Steady State voltage Stability using

SVC and TCSC”, National Conference on

Recent Trends in Engineering and

Technology. pp 13-14.

10. Rahul Somalwa and Manish Khemariya,

(2012) “A Review of Enhancement of

Transient Stability by FACTS Devicces”,

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Technologies in Sciences and

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11. Samima Akter, Anjulelkha saha and

Pryananath Das (2012), “Modelling,

Simulation and Comparison of various

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Research and Technology, 1(8).

12. Anulekhasaha Priyanath Das and Ajoy

Kumar chakraborty (2012), “performance

analysis and Comparison of Various

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International Journal of computer

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13. Dipti, M; Aziz, A and kheen, M.A. (2013)

Modeling, Simulation and Performance

Analysis of FACTS Controller in

Transmission Line. International Journal

of Emerging Technology and Advanced

Engineering. 3(5). Pp 428-435.

14. Pardeep, S.V and Vijay, K.G. (2013)

Power System Stability Improvement of

Long Transmission Line System by Using

Static Var Compensator (SVC). Int.

Journal of Engineering Research and

Applications. 3(5). pp. 01-03.

15. N. Hingorani (1991), -FACTs – Flexible

ac transmission systems,1 in Proc. IEEE

5th Int. Conf. AC DC Transmission,

London, U.K., Conf. Pub. 345. pp. 1-7.

16. N.G. Hingorani and L. Gyugyi (2000),

Understanding FACTS: Concepts and

Technology of Flexible AC Transmission

Systems. New York: Willey, vol.1.

17. Mathur, R. Mohan and Varma, Rajiv K., -

Thyristor-based Facts Controllers for

Electrical Transmission System, John

Willey & Sons.

18. Nang Sabai, and Thida Win (2008)

“Voltage control and dynamic

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pp. 425-429.

AUTHOR’S PROFILE

Oyedoja, K.O. received is B.Eng., M.Eng., in

Electrical Engineering from University of Ilorin,

Nigeria, Msc in Industrial and Production

Engineering from University of Ibadan, Nigeria,

respectively. At present, he is with the Department

of Technical Education, EACOED, Oyo, Oyo


Oct. 2014. Vol. 5. No. 05 ISSN2305-8269


50

State, Nigeria and working towards his Ph.D. His

research interests are Artificial intelligent, Digital

signal Processing, Neural Network, fuzzy logic,

Matlab, etc.

Appendix 1

Figure 9. Detailed model of Nigeria 31-bus high voltage network in PSAT

(Kanji)

Hydro


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