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  • 1. Paper presented in the National conference on Energy Management 2009, at Engineering Collage Bikaner held on 20-21 Nov. 2009
  • 2. LabVIEW Based Simulation of TCSC FACTS Controller Arun Kumar Swami (Student, M E Instrumentation and Control) Mrs. Lini Mathew (Assistant Professor) Dr. S. Chatterji (Professor and Head) Department of Electrical Engineering N.I.T.T.T.R., Chandigarh. ABSTRACT Power is an essential requirement of our life. The demand of power in India is enormous and is growing steadily. However, because of lack of available investments, the development of new transmission systems in the country does not follow the increase in power demand. Power system engineers are currently facing challenges to increase the power transfer capabilities of existing transmission system. As such, it is necessary to utilize the existing power transmission system at its maximum capacity to meet increasing demand of electrical energy. Flexible AC Transmission System (FACTS) controller can balance the power flow and there by using the existing power system network most efficiently. Thyristor controlled series compensator (TCSC), is the first generation of FACTS controller, can continuously control line impedance through introduction of a thyristor controlled capacitor in series with the transmission line. TCSC is used as series compensator in transmission system, it can be designed to control the power flow in order to increase the power transfer limits or to improve the transient stability. The TCSC controller can provide a very fast action to increase the synchronization power through quick changing of the equivalent capacitive reactance to the full compensation in first few cycles after a fault, hence subsequent oscillations are damped. In the present work author simulated the TCSC using LabVIEW software, the design of TCSC controller has been done using transfer function model. The advantage of using transfer function model is that the change in rotor speed can be directly converted into compensation required by the TCSC.
  • 3. I INTRODUCTION Power is an essential requirement for all facets of our life and has been recognized as a basic human need. It is the critical infrastructure on which the socio- economic development of the country depends. The demand of power in India is enormous and is growing at a very high pace. By the year 2012, India s peak demand would be 157107 MW. It is essential to raise the amount of transmitted power preferably with existing transmission facilities in order to meet the increasing demand. Because of lack of available infrastructures, the development of new transmission systems in the country does not follow the increase in power demand. Hence, there is a gap between transmission capacity and actual power demand, and as a consequence, some transmission lines are loaded more than were planned when they were built. With increased load on transmission lines, the problem of transient stability due to a major fault can very well become a transmission power-limiting factor. The power system must adapt to momentary system conditions, or in other words, power system should be flexible in nature. This concept has given birth to the term called the Flexible AC Transmission System (FACTS). The first generation FACTS devices namely Static Var Compensator (SVC) and Thyristor Controlled Series Compensator (TCSC) have been introduced in1980s. II POWER SYSTEM STABILITY Stability of power system has been a major concern in electrical power system operation. This arises from the fact that in steady state, the angular speed of all the generators must remain the same, anywhere in the system. This is termed as synchronous operation of a system. Any disturbance small or large can affect the synchronous operation. Stability as per IEE can be defined as: That attribute of a system which enables it to develop restoring forces between elements there of equal or greater than disturbing forces so as to restore a state of equilibrium between elements. A power system is said to be in steady state stable condition (for a particular operating condition) if following any small and gradual disturbance, it reaches a steady state operating condition which is identical or close to the pre disturbance operating
  • 4. condition. The transient stability can be defined as the capability of the power system to maintain synchronism when subjected to a severe disturbance. The transient state stability refers to the maximum flow of power possible through a point without losing the stability with sudden and large changes in the network conditions brought about by faults, or by sudden large increment of loads. The maximum power, which can be transmitted within transient stability, is known as the transient stability limit. III FACTS TECHNOLOGY FOR TRANSIENT STABILITY ENHANCEMENT The loss of transient stability in a power system is due to overloading of some of the lines or due to severe line faults, as a consequence of tripping off of the other lines after faults or heavy loss of loads. By means of rapid and flexible control over the ac transmission parameters and network topology, FACTS technology can facilitate power control, enhance the power transfer capacity, decrease the line losses, increase power system damping and improve the stability and security of the power system. The TCSC controller can provide a very fast action to increase the synchronization power through quick changing of the equivalent capacitive reactance to the full compensation in first few cycles after a fault, hence subsequent oscillations are damped. IV THYRISTOR CONTROLLED SERIES COMPENSATOR A Thyristor controlled series capacitor (TCSC) improves the overall performance of the series compensated electrical power system due to fast and flexible control of the effective reactance produced by the TCSC. In addition, ability of TCSC to effectively damp sub-synchronous oscillations makes it a versatile electrical power systems stability controller. In conjunction with series capacitors, it can generate reactive power that increases with line loading, thereby aiding the regulation of local network voltages. During events of high short circuit current, the TCSC can switch from the controllable-capacitance to the controllable-inductance mode, there by restricting the short circuit currents. Thyristor controlled series compensator (TCSC) is an effective and economical means of solving problems of transient stability, dynamic stability, steady
  • 5. state stability and voltage stability in long transmission lines. Many relevant benefits such as better utilization of transmission capability, efficient power flow control, transient stability improvement, power oscillation damping, and fault current limitation etc can be achieved by adjusting the reactance of the TCSC flexibly and quickly. TCSC can control the line impedance through the introduction of a thyristor- controlled capacitor in series with the transmission line and there by continuously control the power flow by quickly changing the effective reactance of line. The basic module of a TCSC is shown in Fig.1. It has a series capacitor C, in parallel with a thyristor-controlled reactor, Ls as shown in Fig.1, whereas a simplified TCSC circuit is shown in Fig.2 for analysis purpose. Fig. 1. Basic Module of a TCSC Fig. 2. Simplified TCSC circuit Transmission line current is assumed to be the independent variable and is represented as variable current source, is(t). For the analysis purpose, the line current is assumed to be sinusoidal. The equivalent TCSC reactance is represented by: XC2 s + sin s 4XC2 cos 2 (s 2 ) (k tan k (s 2 ) - tan (s 2 )) X TCSC = X C - + (X C - X P ) p ( (X C - X P ) k 2 - 1 ) p (1) where, XC is the reactance of capacitor XP is the reactance of inductor connected in parallel with capacitor is conduction angle
  • 6. V SYSTEM M ODELING WITH TCSC CONTROLLER USING LABVIEW Fig. 3. shows the single-line diagram of SMIB power system with TCSC controller. The swing equation of a synchronous machine may be represented in state space form as: dw 1 = ( PM - Pe - Pd ) pu/sec. (2) dt M = 0( -1 ) elec rad/s (3) , E Vt where, Pe = , sin d pu (4) Xd E ' = Vt + jX d I pu ' (5) dw Where, M is the accelerating power. dt VS Vt V0 Xdd ZL TCSC Generator Fig. 3 SMIB System with TCSC Controller Electrical power S =Pe +jQe (6) also S =vt.i vt - V0 i= (7) ZL Fig. 4 LabVIEW Simulation Model of TCSC Controller The TCSC controller model is shown in Fig. which rotor angle is input and deviation in conduction angle is output. Initial conduction angle is added with it and the
  • 7. output that is sigma is given as input along with XC and X P to sigma to XTCSC sub VI to find out corrected value of XTCSC as shown in Fig. 4. The SMIB power system with TCSC controller is simulated as shown in Fig.5. The TCSC controller model is incorporated in this model. The complete simulation system has been developed using LabVIEW software is shown in Fig. 5. Fig. 5 LabVIEW Simulation of SMIB Power System with TCSC Controller VI SIMULATION RESULTS The effectiveness of a TCSC controller for enhancing the transient stability performance of a power system has been analyzed for different conditions. For the different values of damping constant k, the rotor angle (delta) versus time curve has been analyzed at various instants of time. Fig. 4 represents the rotor angle (delta) vs time curve for damping constant k=5. From this curve, it has been analyzed that at t = 5 sec., rotor angle reaches its maximum value at 80 degrees. At this point, system becomes unstable. To bring back the system to
  • 8. stability, the TCSC controller injects a particular value of voltage in the transmission line. With the result of this voltage, rotor angle decreases to 25 degrees at t =30 sec., and finally between instants 65 to 70 sec. rotor angle is stable at around 28 degrees. Fig. 6 Rotor Angle Variation with Time for k = 5 As the values of damping constant is increased to 10, 15, 20, 25, 30 and 40 respectively, the system attains stability at a faster rate and oscillations are also reduced Table 1 provides the tabulated results which show that the system attains stability after 15 sec. when the value of damping constant k = 35 as compared to 70 sec for k = 5. This is shown in Fig.5. Table 1 Time taken to Attain Stability of Rotor Angle with Damping Constant k Damping Time taken to attain Final sigma value Constant stability (deg) k (sec) 5 68-72 60 10 40-42 60 20 24 60 30 18 60 35 15 60
  • 9. Fig. 7 Rotor Angle Variation with Time for k = 35 CONCLUSION The analysis shows that if compensation is provided through TCSC controller, then system attains stability at faster rate. The Stability of the system depends upon reactance of TCSC controller. The value of TCSC controller reactance changes with the change in conduction-angle of the thyristor in TCSC controller which is governed by the rotor-angle. The analysis shows that with changes in the value of damping constant (k) keeping the controller gain (K) at a constant value the time taken by the system to attain stable state reduces significantly. This is due to the fact that by increasing damping constant (k) the oscillations in the system are reduced and the rotor attains stability faster. REFERENCES [1]. Chatterji. S, Rao .C. S., Nagsarkar T. K., Application of FACTS Controllers for improving Power System Stability , Xll National Conventions of Electrical Engineers- Power System Management to overcome power shortage, Institution of
  • 10. Engineers(INDIA) Punjab,Haryana and Chandigarh State Center Chandigarh, 23-24Nov., 1996. [2]. Chatterji. S., Rao.C.S., Nagsarkar T.K., Admittance Chacteristics of Thyristor Controlled Dynamic Brake, 9th National Power Systems Conference, IIT Kanpur, 19-21 Dec., 1996. [3]. Chatterji. S., Rao.C.S., Nagsarkar T.K., Fuzzy Logic based Half Wave Thyristor Controlled Dynamic Brake , 5th International Conference on Power Electronics and Drive Systems(PEDS-2003) organized by IEEE in Singapore, 17-20 Nov., 2003. [4]. J. J. Paserba, How FACTS Controllers Benefit AC Transmission Systems , IEEE Power Engineering Review, 2003. [5]. Mathur R.M., Varma R.K.,Thyristor based FACTS Controllers for Electrical Transmission systems,IEEE Press, series on power engineering ,Pis cataway, 2002. [6]. Edris A. FACTS Technology Development; An Update , IEEE Power Engineering Review, March, 2000. [7]. Edris A., Determination of Needed FACTS Controllers that Increase Asset Utilization of Power Systems , IEEE Power Engineering Review 1996. [8]. Alberto D. Del Rosso, Claudio A. Cañizares, ,and Victor M. Doña A Study of TCSC Controller Design for Power System Stability Improvement . IEEE Transactions On Power system vol. 18, issue 4, Nov., 2003, pp. 1487-1496. [9]. Mahajan Vasundhra "Thyristor Controlled Series Compensator", IEEE International Conference on Industrial Technology, ICIT 2006. 15-17 Dec., 2006 pp.:182 - 187 [10]. P. Singh, L. Mathew, Chatterji. S, Simulink based simulation of TCSC in single machine Infinite Bus system. Journal of Engineering & Technology Education, NITTTR , Chandigarh Vol.1, No 2, July- Dec 2007. [11]. Ishida, F.; Taniguchi, H.; Egawa, M.; Fujita, H.; Konishi, H.; Watanabe, M.; ,"Analogue Simulation Studies with Actual Controllers for TCSC" Technology, 1998. Proceedings of. POWERCON '98. 1998 IEEE International Conference on Power SystemVol. 1, 18-21 Aug., 1998 pp.:367 371. [12]. Li Kejun, Zaho Jianguo, Gao Hongxia, "An Experimental Device for Thyristor Controlled Series Compensator Dynamic Simulation", IEEE Power Engineering Society General Meeting,. 24-28 June, 2007 pp.:1 6.