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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 3, March 2012)

7

Simulation and Analysis for Real and Reactive Power

Control with Series Type FACTS Controller

Vatsal J. Patel

1

, C.B.Bhatt

2

1

PG Student, Electrical Engg. Department, Nirma University, SG Highway, Ahmedabad, Gujarat, India.

2Asst. Prof. Electrical Engg. Department, Nirma University, SG Highway, Ahmedabad, Gujarat, India.

110meee12@nirmauni.ac.in

2

chanaykya.bhatt@nirmauni.ac.in

Abstract—A Thyristor controlled series capacitor (TCSC) belongs to the flexible alternating current transmission systems (FACTS) family of devices. It is a variable capacitive and inductive reactance device that can be used to provide series compensation in power transmission lines. One of the significant advantages that a TCSC has over other series compensation devices is that the TCSC's reactance is instantaneously and continuously variable. This means that the TCSC can be used not only to provide series compensation but can also be used to enhance the stability of the power system. In this paper, performance of TCSC is analyzed. Initially, Real and reactive power flow through the transmission line have been analyzed for fixed and then after the same parameters are evaluated by inserting controllable capacitor in the same transmission network. The considered topology of TCSC consists of back to back thyristors that controls the reactance of the TCSC. By changing the firing angle of these back to back thyristors it is possible to vary the reactance of the TCSC. As per the TCSC characteristics, in inductive region at the firing angle α=900 to 1300 the power flow decreasing and in capacitive region at the firing angle α=1400

to 1800 the power flow increasing. For the simulation 3-phase model degree of compensation is 0.55, to increase power transfer capability. The simulation is carried out by using software package MATLAB ©/simulink.

Keywords TCSC, FACTS, Power flow control, Power system, Modelling of TCSC.

I. INTRODUCTION

The world's first Series Compensation on transmission level, counted nowadays by the manufacturers as a FACTS-device, went into operation in 1950. Series Compensation is used in order to decrease the transfer reactance of a power line at rated frequency. A series capacitor installation generates reactive power that in a self-regulating manner balances a fraction of the line's transfer reactance. The result is that the line is electrically shortened, which improves angular stability, voltage stability and power sharing between parallel lines.

Series Capacitors are installed in series with a transmission line, which means that all the equipment has to be installed on a fully insulated platform. Significant device from the group FACTS is a TCSC, which finds application in solving many problems in the power system. Its properties can increase the power lines transmission capacity and power flow control. It also provides a wide range of other uses to ensure effective, trouble-free and economical operation of power systems. Simulation behaviors of these devices are very important before the real deployment of these devices to the power system. Various computing and simulation programs, which help in understanding the activities and setting appropriate parameters of these devices, have found its application to modeling and simulating these devices.

N. G. Hingorani and L. Gyugyi in [1] gives The information about all series type facts controller design and the basic definition, which define that how the series facts controller are differ from the shunt controller for the compensation of reactive power. Mathur R. Mohan and Rajiv K. Varma in [2] described TCSC advantages, modes of operation, controller, Analysis of TCSC, capability characteristics, harmonic performance, losses and modeling of TCSC. The operation, reactance characteristic and resonance condition of TCSC from the paper [3] of resonance behavior, For increasing power transfer capability the better degree of compensation in region between 0.3 to 0.7. The reactive power at the receiving end side is controlled using TCSC at different firing angle to verify the TCSC characteristics curve[4]. The main aim of this paper is to analyze the design of a TCSC controller for stability enhancement, under normal operation and fault conditions at different load power flows.

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 3, March 2012)

8 In this paper the simulation on parallel line with different load and different firing angle to evaluated performance of TCSC characteristics in inductive region and capacitive region for the control the reactive power at the receiving end. The paper is structured as follows: Section II gives the introduction about the basic TCSC scheme and operation of TCSC controller. Section III briefly describes the control scheme of a typical TCSC controller. In Section IV the reactive power control at the receiving end side by using TCSC. In Section V modeling of the TCSC using two parallel line in MATLAB simulation programmed. Simulation & results are showed in Section VI. The conclusion is presented in section VII.

II. TCSC

The Thyristor Controlled Series Capacitor (TCSC) belongs to the Flexible AC Transmission Systems (FACTS) group of power systems devices. The concept of the TCSC has been around since the mid 1980s, with the first known commercial installation being in 1992 in the United States of America. The TCSC controller was developed for the Kanpur-Ballabhgarh 400kV single circuit

ac transmission line located in North India. 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 (FC) in a series compensated line through appropriate variation of the firing angle α. This enhanced voltage changes the effective value of the series-capacitive reactance. Essentially a TCSC is a variable reactance device that can be used to provide an adjustable series compensating reactance to a transmission line. Its advantage over other series compensating devices is that its reactance can be instantaneously and precisely controlled.

[image:2.612.328.572.138.246.2]

A TCSC consists of a fixed capacitor in parallel with a variable inductive reactance as shown in Fig. 1. This variable inductive reactance is obtained by connecting back to back thyristors in series with a fixed-reactance inductor, and is known as a Thyristor Controlled Reactor or TCR. By controlling the trigger angle of the back to back thyristors, it is possible to vary the effective inductive reactance of the TCR, and hence control the reactance provided by the TCSC.

Fig. 1 Basic Thyristor-Controlled Series Capacitor scheme

The reactance of the TCSC can be capacitive or inductive, depending on the trigger angle of the back to back thyristors; The capacitive reactance characteristic of the TCSC is a highly non-linear function of the trigger angle of the back to back thyristors, The TCSC consists of the series compensating capacitor shunted by a Thyristor-Controlled Reactor. In a practical TCSC implementation, several such basic compensators may be connected in series to obtain the desired voltage rating and operating characteristics. 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 continuously variable reactive impedance, controllable by delay angle α. The steady state impedance of the TCSC is that of a parallel LC circuit, consisting of a fixed capacitive impedance XC.

The variable inductive impedance XL(α):-

XL(α) =XL

2

sin

, XL ≤ XL(α) ≤ α.

The impedance of TCSC:-

XTCSC(α) =

.

( )

( )

C L

L C

X X

X

X

The effective reactance of TCSC operates in three region:-

1. Inductive region:- 0 ≤ α ≤ αLlim.

2. Capacitive region:- αClim ≤ α ≤ 90.

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 3, March 2012)

[image:3.612.49.299.141.356.2]

9

Fig. 2 Reactance Vs firing angle characteristic curve.

III. TCSCCONTROLLER

The main principles of the TCSC concept are two; firstly, to provide electromechanical damping between large electrical systems by changing the reactance of a specific interconnecting power line. Secondly, the TCSC shall change its apparent impedance for sub-synchronous frequencies, such that a prospective subsynchronous resonance is avoided.

There are essentially three modes of TCSC operation:- 1. Bypassed-Thyristor mode:- 2. Blocked-Thyristor Mode:-

3. Partially Conducting Thyristor, or Vernier, Mode:-

In the Fig. 3 shows that A metal-oxide varistor (MOV), essentially a nonlinear resistor, is connected across the series capacitor to prevent the occurrence of high-capacitor over voltages. Not only does the MOV limit the voltage across the capacitor, but it allows the capacitor to remain in circuit even during fault conditions and helps improve the transient stability. The circuit breaker (CB) is installed across the capacitor for controlling its insertion in the line. In addition, the CB bypasses the capacitor if severe fault or equipment-malfunction events occur. A current-limiting inductor (LD) is incorporated in the circuit to restrict both the magnitude and the frequency of the capacitor current during the capacitor-bypass operation.

Fig. 3 TCSC Module

If the TCSC valves are required to operate in the fully ―on‖ mode for prolonged durations, the conduction losses are minimized by installing an ultra–high-speed contact (UHSC) across the valve. This metallic contact offers a virtually lossless feature similar to that of circuit breakers and is capable of handling many switching operations. The metallic contact is closed shortly after the thyristor valve is turned on, and it is opened shortly before the valve is turned off. During a sudden overload of the valve, and also during fault conditions, the metallic contact is closed to alleviate the stress on the valve.

IV. REACTIVE POWER COMPENSATION BY TCSC

[image:3.612.333.563.144.355.2]
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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 3, March 2012)

10 The total current passing through the TCSC is sinusoidal; the equivalent reactance at the fundamental frequency can be represented as a variable reactance XTCSC.

There exists a steady-state relationship between α and reactance XTCSC. In power transmission applications, the

degree of compensation is usually chosen in the range 0.3 ≤ k ≤ 0.7. The relationship can be described the following equation:-

2 2

2 ( )

2

( ) (k tan( )) (tan( ))

sin 4X 2 2 2

- +

( ) 1

C C

TCSC C

C L C L

k cos

X

X X

X X X X k

  

 

 

 

 

where,

XC= nominal reactance of the fixed capacitor C.

XL= Inductive reactance of inductor L connected in parallel

with C. σ=2(π-α),The conduction angle of TCSC controller.

k= C

L

X

X

,

The Compensation Ratio.

V. MODELLING OF THE TCSCBY USING

MATLAB SIMPOWER SYSTEM

For demonstration of action TCSC device, from the viewpoint of active power flow control has been created a simple model of electrical network, in which was subsequently implemented TCSC device. The model of simple electrical network consists of a voltage source, load, two parallel lines and units for measuring and displaying measured electric variables.

Fig. 4. Block diagram of the model of electrical network with TCSC.

The degree of compensation for this simulation model is 0.55, so that power transfer capability is increase. In power transmission applications, the degree of compensation is usually chosen in the range 0.3 ≤ k ≤ 0.7

.

For simulation purpose using two parallel line in which first fixed capacitor compensation applied in one line and then TCSC is applied into that line.

In this electrical network during the simulation process with and without TCSC, a LLLG fault is applied at receiving end bus. The fault is cleared by breaker in 0.04s. The purpose of simulation for parallel line is to increase power transfer capability with used of TCSC controller. In the first case without TCSC fixed capacitor the power transfer is lower and adding a TCSC controller in one of line as per simulation model the power transfer capacity increase with different firing angle.

[image:4.612.327.567.250.446.2]

VI. SIMULATION &RESULTS

Fig. 5 3-phase Series compensation by conventional method.

[image:4.612.52.300.481.597.2]
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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 3, March 2012)

[image:5.612.325.573.132.518.2]

11 By using fixed capacitor compensation method the fixed capacitor value is 220µF. The LLLG fault is applied on receiving end side bus and breaker is operating 0.04s to clear a fault. In Fig. 9 result show that a receiving end power by conventional method. The receiving end power by Without TCSC is P=294MW and Q=147.5MVAR.

Fig. 6 Receiving end power by conventional method

Inclusion of TCSC device to one of the lines changes the power flow in given lines according to level desired. This change is achieved by changing the impedance of line, in which is installed TCSC device. With the entry values of angle switching thyristors α, TCSC can change the impedance of the line and thereby regulates the power flow as required. When such a change power flow, the power flow on lines is reallocated to another ratio, but the

[image:5.612.54.309.216.382.2]

resulting flow performance remains unchanged.

Fig.7 Series compensation by TCSC Controller for close loop

Fig. 8 Receiving end power at the firing angle α=900

Fig. 9 Receiving end power at the firing angle α=1800

In Fig. 8 is showed situation in the modeled electrical network at adjusted angle α = 90°. Impedance of TCSC is inductive and therefore there is a change in power flow on lines No.1 and No.2. This value of the angle of switching leads to decrease power flow on line, whose value has reduce from the original value of P = 285.5 MW to Q = 142.7 MVAR (measured at the load).

[image:5.612.51.295.412.681.2]
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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 3, March 2012)

12 TABLE I

POWER FLOW IN THE LINE AT THE LOAD P=300MW AND Q=150MVAR

Firing Angle α

Power Without TCSC

900 1300 1400 1800

P(MW) 294 285.5 284.1 298.7 295.8

Q(MVAR) 147.5 142.7 141.5 148.6 147.9

TABLE II

POWER FLOW IN THE LINE AT THE LOAD P=300MW AND Q=200MVAR

Firing Angle α

Power Without TCSC

900 1300 1400 1800

P(MW) 292.2 273.8 272.4 297.8 294.3

Q(MVAR) 194.8 182.5 182.29 198.1 196.1

As per table data at firing angle α= 900

to 1300 as a inductive action of the TCSC the power flow into the line in decreasing manner. In the case of capacitive operation, when capacitance TCSC acts on impedance of line No.1, will decline impedance of line No.1 and thereby will increase the power flow through the line No.1 and reduced the power flow through the line No.2. The results shows at firing angle α=1400

to 1800, the power flow in line increasing compare with conventional method(without TCSC). The table also shows result for different load and firing angle to verify the TCSC reactance Vs firing characteristics curve in Fig. 2.

VII. CONCLUSION

The TCSC is controlling the reactive power and voltage stability limit better than convectional compensation method by changing the firing angle of the back to back thyristors. From the simulation point of view, TCSC can control the power at the different load condition and also in different firing angle of thyristors.

The result of convectional compensation and TCSC compensation method shows that the power is decreasing in case of TCSC compensation at the firing angle between 900 to 1300(inductive mode region) and the power is increasing at the firing angle between 1400 and 1800 (capacitive region). The degree of compensation is 0.55 for this simulation model, so the power transfer capability increases.

REFERENCES

[1] N. G. Hingorani and L. Gyugyi, “Understanding FACTS

Concepts and Technology of Flexible AC Transmission Systems”, IEEE Press. New York, 1999.

[2] R. M. Mathur and R.K. Varma, “Thyristor based FACTS

Controllers for Electrical Transmission Systems”, IEEE press,Piscataway 2002.

[3] Rajesh Kumar Nema S. Meikandasivam and Shailendra Kumar Jain.

“Selection of TCSC parameters capacitor and inductor”. Martin German-Sobek, _ubomír Be_a, Roman Cimbala,” Using of

the Thyristor Controlled Series Capacitor in Electric Power System”. ELEKTROENERGETIKA, Vol.4, No.4, 2011.

[4] User’s Guide of MATLAB R 2011a.

APPENDIX

The parameters of the model are as follows: Ideal Three-Phase Voltage Source Line to-line voltage VLL = 400 kv,

Phase angle φ= 0°, Frequency f = 50 Hz, Three-Phase Parallel RL Load Active power P = 300 MW, Reactive power Q = 150 MVAr, Configuration Y (grounded), Three-Phase PI Section Line n.1 and n.2 Line resistance R = 0.028Ω/km, Line inductance L = 0.904 mH/km, Line capacity C = 0.012707µF/km, Line length l = 100 km,

Maximum current of line Imax = 1200 A.

According to parameters the line series impedance is Z=0.028+j0.28386. The line series reactance is XL =0.028386/km*100km

XL=28.386Ω

The Capacitive reactance TCSC devices is XC=15.688Ω.

Percentage of compensation can be = XC/XL*100 =55.27%

Figure

Fig. 1 Basic Thyristor-Controlled Series Capacitor scheme
Fig. 3 TCSC Module
Fig.5 MATLAB/SIMULINK
Fig. 9 Receiving end power at the firing angle α=1800

References

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