International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013) Modeling and Analysis of SVC, TCSC, TCPAR in Power Flow Studies N. M. G. Kumar, P. Venkatesh, Dr. P. Sangamewara Raju 1 Research Scholar, 3Professor, Dept of EEE, Sri Venkateswara University, Tirupati, India, 2 Asst .Prof, Dept of EEE, Sree Vidyanikethan Engineering College, Tirupati, India Abstract — The paper mainly deals about the application of flexible AC transmission system (FACTS) to increase the power transfer capabilities for new operating scenarios in the bulk power systems. With the effect of FACTS technology improves transmission capabilities to reduce the system losses, and also improves the loadability of the power system. FACTs technology allows a better utilization existing transmission and generation reserve margins in the deregulated electricity market for various stability margins. In this paper discusses about the study state models of SVC (Static VAR Compensator), TCSC(Thyristor Controlled Series Compensator) and TCPAR (Thyristor Controlled phase angle regulator) is investigated for load flow environment to enhance the power transfer limits. A proposed algorithm has been tested on IEEE – 5 bus and 30 bus system in a specified line under voltage stability limits and results are tabulated. The proposed technique is simple and able technique to improve the system operation under study state condition. In most of the reported studies, attention has been focused on the ability of these devices to improve the power system security by damping system oscillations and minimal attempts have been made to investigate the effect of these devices on power system reliability. The opportunities arise through the ability of FACTS controllers to control the interrelated parameters that governs the operation of transmission systems including series impedance and shunt impedance, current, phase angle and damping of oscillations at various frequencies below the rated frequency. These constraints cannot be overcome otherwise, while maintaining the required system stability, by mechanical means without lowering the useable transmission capacity. By providing added flexibility, FACTS controller can enable a line to carry power closer to its thermal rating. Mechanical switching needs to be supplemented by rapid-response power electronics. The facts technology can certainly be used to overcome any to the stability limits, in which case the ultimate limits would be thermal and dielectric. Static VAR controllers control only one of three important parameters (voltage, impedance, phase angle) determining the power flow in the AC power system viz. the amplitude of voltage at selected terminals of transmission line . It has long been realized that an all solid-state or advanced, static VAR compensator, which is true equivalent of ideal synchronous condenser, is technically feasible with the use of Gate Turn-Off (GTO) Thyristor. The UPFC is recently introduced FACTS controller which has the capability to control all the four transmission parameters. The UPFC not only performs the functions of STATCOM, TCSC, and the phase angle regulator but also provides additional flexibility by combining some of the functions of these controllers. Most of the world’s electric supply systems are widely interconnected. This is done for economic reasons, to reduce the cost of electricity and to improve its reliability, it must however be kept in mind that these inter connections are very complex and they emerged gradually based upon the requirements of various power utilities. Keywords— Static VAR compensator, Thyristor Controlled Series Compensator (TCSC), Thyristor Controlled phase angle regulator (TCPAR), Newton – Raphson method , power flow. I. INTRODUCTION TO FACTS DEVICES The ability to control power flow in an electric power system without generation rescheduling or topology changes can improve the power system performance using controllable components, the line flows can be changed in such a way that thermal limits are not exceed, losses are minimized, stability margins are increased and contractual requirements are fulfilled without violating the economic generation dispatch. Flexible AC Transmission systems (FACTS) technology is the ultimate tool for getting the most out of existing equipment via faster control action and new capabilities. The most striking feature is the ability to directly control transmission line flows by structurally changing parameters of the grid and to implement highgain type controllers based on fast switching. The application of FACTS devices to power system security has been an attractive ongoing area of research. 418 International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013) These interconnections apart from delivering the power pool power plants and load centres in order to pool power generation and reduce fuel cost. Thus they reduce the overall number of generating sources, but as the saying goes a coin has two sides, like wise as the power transfer grows. The power system becomes increasingly complex to operate and system can become less secure for riding through major outages. It may lead to large power flows with inadequate control, excessive reactive power, and large dynamics wings between different parts of the system. Thus the full potential of a transmission connection cannot be utilized. It is very difficult to control such transmission of power in such systems. Most of the controllers designed in the past were mechanical in nature. But mechanical controllers have numerous intrinsic problems. Many power electronics controllers have been designed to supplement the potentially faulty mechanical controllers. These power electronic controllers are all grouped in a category called flexible AC transmission controller or FACTS controllers. Facts technology opens up new opportunities for controlling power and enhancing the usable capacities of present, as well as new and upgraded lines, the possibility that current through a line can be controlled at a reasonable cost enables large potential of increasing the capacity of existing lines with large conductors. Also, the use of one of the FACTS controllers to enables corresponding power flow through such lines under normal and contingency conditions. These opportunities arise through the ability of FACTS controllers to control the interrelated parameters that govern the operation of transmission system. ―Series Impedance, Shunt Impedance, Current, Voltage, Phase angle etc.,‖ are some of the interrelated parameters that are controlled. These constrains cannot be overcome while maintaining the system reliability by mechanical means without lowering the usable transmission capacity. By providing added flexibility FACTS controllers can enable a line to carry power closer to it thermal rating. It must however be emphasized that FACTS is an enabling technology, and not a one to one substitute. The FACTS technology is not a single high power controller but rather a collection of controllers, which can be applied individually or in co-ordination with others to control one or more of the interrelated system parameters mentioned above. A Wellchosen FACTS controller can overcome specific limitations of designated transmission line on a corridor. But all FACTS controller represent applications of some basic technology, their production can eventually take advantage of technologies of scale. Just as the transistor is the basic element for whole variety of microelectronic chips and circuits, the thyristor or high power transistor is the basic element for a variety of high power electronic controllers. FACTS technology also lends itself to extending transmission limits in a step-by-step manner with an incrementing investment as and when required. A planner could force a progressive scenario of mechanical switching means and enabling FACTS controllers such that the transmission lines will involve a combination of mechanical and FACTS controller to achieve the objective in an appropriate, stage investment scenario. It is also worth nothing that in implementation of the FACTS technology, we are dealing with base technology, proven through HVDC and high power industrial drives. Nevertheless, as power semiconductor devices continue to improve, particularly the devices with turn off capability cost of FACTS controller tend to decrease. II. BASIC CONCEPTS AND PROBLEM FORMULATION N-R METHOD: The most widely used method for solving simultaneous nonlinear algebraic equations is the Newton-Raphson method (NR). Newton’s method is found to be more efficient and practical. The number of iterations required to obtain a solution is independent of the system size, but more functional evaluations are required at every iteration. Since in the power flow problem real power and voltage magnitude are specified for the voltage-controlled buses, the power flow equation is formulated in polar form. This equation can be rewritten in admittance matrix as n I i YijV j ….(1) j 1 In the above equation, j includes bus i. expressing this equation in polar form, we have n …. (2) I i | Yij || V j | ij j j 1 The complex power at bus i is Pi jQi Vi * I i Ii in equation 3 Pi jQ j | Vi | i | Yij ||| V j | ij j ….(4) Substituting form equation 2 for n j 1 419 .… (3) International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013) Separating the real and imaginary parts, n Pi | Vi | | V j || Yij | cos( ij i j ) j 1 ….(5) ….(10) B | Z | , .… (11) n Qi | Vi | | V j || Yij | sin( ij i j ) j 1 J1 P Q J 3 J 2 J 4 | V | Z ) | A | 2 X tan1 R A (1 YCP * 1 2 ….(6) …. (12) If series compensation is provided, then: tan 1 ….(7) By running the load flow analysis using NR-method we can fine the Power flows in individual lines and loss …. (13) X XC R Now assume that power flow in a line is to be regulated to a desired value (Pspecified) Psp, then the corresponding new value of B i.e. Bnew can be found out using the equation given below III. MODELING OF FACTS DEVICES (1) Static VAR compensator (SVC): In this paper, Static VAR compensator is considered as simple injecting the reactive power into the transmission line. Bnew | V1 || V2 | cos( ) | A || V2 | cos( ) … (14) Pspecified Note that Bnew is also given by the equation 1 Bnew ( R 2 ( X X C ) 2 ) 2 from which Xc can be calculated. Consider the initial line reactance X = Xline of uncompensated. With the Xc in the line the resultant line reactance is given by X = X - Xc .... (15) The equation (14) is a highly nonlinear equation and need to be solved iteratively and update X using eqn. (15) accordingly. With the series compensation in the line X X C will be small compared to β of the tan 1 ( ) R uncompensated line. Keeping this fact in mind, the X c calculations can be made in three stages as mentioned below. Fig.1. Reactive power injected model of SVC SVC can be used for both inductive and capacitive compensation. In this project work the SVC is modelled as an ideal reactive power injection at bus i. i.e Qi QSVC .… (8) (2) Thyristor-controlled series compensator (TCSC) Consider a transmission line with its ABCD parameters as two port model shown below figure 2 A. Stage 1 Calculate β = tan-1 (Xline / Rline), from uncompensated condition. Then considering incremental approach to avoid the higher correction step, take β1=50% of βold .... (16) Then solve equation (14) for finding Bnew using the V11 and V2 2 of the desired line obtained from the converged voltages of base case loads flows. The corresponding Xc will be X-Xc = (Bnew2 – R2)1/2 .… (17) With this Xc in the line compensation reactance, the resulting reactance is X=X-Xc .... (18) Fig.2. Two port model of a Transmission line The power at the receiving end P2 is given by P2 | V1 || V2 | cos( ) | A || V2 | cos( ) |B| .…(9) 420 International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013) B. Stage 2 (3) Thyristor controlled Phase angle regulator (TCPAR) Mathematical Modeling of TCPAR In this approach the TCPAR is represented in power injection model and it regulates the angle of the transformer in intern to improve power flow and reduce the power system loss. The static representation of TCPAR is shown in Fig. 3. The Line Model with Thyristor Controlled Phase Angle Regulator (TCPAR) has shown in below Fig. 4. The real power flow (Pij) and reactive power flow (Qij) in a linek connected between bus - i and bus - j can be written, without any TCPAR, as With the above resulting X= (X-Xc) as the effective or net reactance of the desired line, re-run the load flow solution. Now new values of voltages of the line end buses i.e. V1 1 and V2 2 are available. Re compute the parameters A=| A |α and B=| B | β1, where β1 from equation (16), and X given by equation (18) As the solution of equation (13) is nearer to the final solution, β2 is to be taken as β2=80% of β1 ……(19) Once again solve equation (14) for finding Bnew using latest values of V11 and V2 2 and update the value of 2 Pij VV i jYij cos(ij i j ) Vi Yij cos ij Qij Vi 2Yij sin ij ViV j sin(ij j i ) X using equations (17) and (18). …..(23) 2 Vi Ysh 2 ….. (24) C. Stage 3 With the above resulting X=(X- Xc) as the effective or net reactance of the desired line, re-run the load flow solution. Now new values of voltages of the line end buses i.e. V1 1 and V2 2 are available. Recomputed the parameters A=| A |α and B=| B | β2; where β2 from equation (19), and X given by equation (18) as the solution of equation (13) is nearer to the final solution, β3 is to be taken as β3 =100% of β2 …….(20) Once again solve equation (13) for finding B new using latest values of V1 1 and V2 2 and update the value of X Fig: 3 Static Representation of TCPAR using equations (17) and (18).Re-run the load flow and compute the Xc and Xfinal. By the completion of the 3rd stage calculations, the accurate value of Xc is available. At every stage of the above approach calculate the power flow (Pcal flow) of the line under consideration and its mismatch between Psp and Pcal flow. Calculate the % error of the flow in the line at the end of 3rd stage. This error indicates the level of accuracy observed in the results produced by the proposed algorithm. Fig: 4. power injection model of TCPAR Where, Vi and i are the voltage magnitude and angle at bus i. Yij and ij are magnitude and angle of ith to jth element of Y Bus matrix. Ysh is the full line charging admittance of line. In a thyristor controlled phase angle regulator, the phase shift is accomplished by adding or subtracting a variable voltage component in perpendicular to the phase voltage of the line. Fig.3 shows the static model of a thyristor controlled phase angle regulator. The effect of TCPAR can be modelled by a series inserted voltage source VT and a tapped current IT. The additional voltage source changes the bus voltage from Vi to Vj1 corresponding to the shifting of the voltage by an angle α. The basic relationships is D. Alternate method using reactance compensation The reactance of transmission line and is compensation factor of TCSC is modeled by changing transmission line reactance as below Xnew =Xline + XTCSC …… (21) XTCSC= rTCSC * Xline …… (22) Where Xline is reactance of transmission line and is compensation factor of TCSC is depended on transmission line where it is located. To prevent overcompensation, TCSC reactance is chosen between -70% of Xline to 20% of Xline . Vi1 e j Vi k V Vi (1 j tan ) 1 i 421 ….. (25) … (26) International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013) VT j tan … (27) Where, k=cosα. is the transformation coefficient of the voltage magnitude and α is the controllable parameter of TCPAR. Neglecting losses in the TCPAR, the current relationships can be written as Vi I i* Vi1 I i1 … (28) j 11 i I e Ii k … (29) I i IT I i1 … (30) IT jI tan … (31) 1 i Fig 5. Test System: IEEE 5 bus system The power flow equations from bus I to bus j can be written as S ij Pij jQij Vi I ij* Vi ( I T I i* )* … (32) Based on this relationship, the real and reactive power flow equations can be written as P tViViYij cos( ij i j ) t 2Vi 2Yij cos ij … (33) Q t 2Vi 2Yij sin ij tVV sin(ij i j ) t 2Vi 2Ysh 2 … (34) Where t=1/ cosα The injection model of TCPAR is shown in Fig: 4.The injected active power at bus- i (Pis) and bus- j (Pjs) and reactive power powers (Qis and Qjs) of a line having phase shifter are Pis Vi 2T 2 g ij ViV j T ( g ij sin ij bij cos ij ) ... (35) Qis Vi Tbij VVT ( g ij cos ij bij sin ij ) … (36) Pjs ViV j T ( g ij sin ij bij cos ij ) ... (37) Q js ViV j T ( g ij cos ij bij sin ij ) … (38) 2 Fig 6. Test System: IEEE 30 bus system V. RESULTS (1) SVC (Static var compenciator) The change in injected reactive power at 4 and 5 buses is 32MVAR Where T=tan gij + jbij is the series admittance of the line connected between bus - i and bus- j.Equations (33) and (34) have been used to model TCPAR in congestion management. Table: 1 Results before and after placement of SVC for IEEE 5 bus System IV. SYSTEM INVESTIGATED Bus No In the paper IEEE 5 and 30 bus system test by using proposed algorithm 1 2 3 4 5 422 Without FACTS phase Voltage angle pu deg 1.060 0.000 SVC at bus 4 phase Voltage angle pu deg 1.060 0.000 SVC at bus 5 Voltage phase angle pu deg 1.060 0.000 1.000 0.984 0.979 0.970 1.000 1.003 1.005 0.979 1.000 0.987 0.984 0.972 -2.245 -3.906 -3.971 -5.570 -2.055 -4.886 -5.285 -5.846 -2.061 -4.637 -4.957 -5.765 International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013) Table: 4(b) line loss without and with SVC Devices for IEEE 30 bus system Total system loss without SVC 6.122 MW, 10.777MVAR, Total system loss with SVC at 5 bus is 6.182 MW, -10.956 MVAR, Total system loss with svc at 4 bus 6.129MW, -11.210 MVAR Table: 2(a) Power flows without and with SVC Devices for IEEE 5 bus Location 2-4 3-4 4-5 2-5 4-5 27-30 29-30 power flows Without SVC With SVC P MW Q MVAR P MW Q MVAR 27.71 -1.72 27.80 -12.92 19.38 2.86 19.65 -12.29 6.59 0.51 6.87 6.05 54.66 5.55 54.95 -17.63 6.59 0.51 6.42 0.06 Total system loss without TCSC 6.122 MW, 10.777MVAR for IEEE-5 bus system. The total system loss without TCSC is 17.599MW, 22.244MVAR for IEEE30 System (2) TCSC (Beta compensation technique) In IEEE 5 and 30 bus system, TCSC is placed in Line: 2-4 Table: 2(b) line loss without and with SVC Devices for IEEE 5 bus system Location 2-4 3-4 4-5 2-5 4-5 Table: 5(a). Power flow and line loss without and with TCSC Devices for IEEE 5 bus system Line losses Without SVC With SVC P MW Q MVAR P MW Q MVAR 0.46 -2.55 0.53 -2.41 0.04 -1.82 0.05 -1.86 0.04 -4.65 0.09 -4.63 1.21 -2.55 1.31 0.93 0.04 -4.65 0.06 -4.77 Beta 1 2 3 4 18 30 Beta Compensation (%) 0% 50% 80% 100% SVC at bus 30 Voltage Phase angle pu deg. 1.060 0.000 1.043 -5.496 1.022 -8.005 1.013 -9.662 1.029 -16.867 1.008 -18.222 Line losses P Q MW MVAR 0.50 -2.51 1.19 -2.65 1.18 -2.64 1.36 -2.77 Reactance X=X-Xc 0.1703 0.1153 0.1132 0.0960 Power flows P Q MW MVAR 36.069 3.705 44.428 1.679 44.813 1.543 48.179 0.161 Line losses P Q MW MVAR 0.699 -1.812 1.041 -1.794 1.059 -1.797 1.219 -1.847 (4) TCPAR (Thyristor controlled Phase angle regulator) For 5 bus system with r = 0.01; gamma=10; alpha=0.5 Table: 6. TCPAR is placed in between the line 2 and 4 in IEEE 5 bus system Table: 4(a) Power flow without and with SVC Devices for IEEE 30 bus system 27-30 29-30 0.176 0.065 0.066 0.051 Power flows P Q MW MVAR 28.02 -8.96 40.22 -21.21 40.30 -21.03 42.16 -24.35 Table: 5(b). Power flow and loss without and with TCSC Devices for IEEE 30 bus system The total system loss without SVC is 17.599MW, 22.244MVAR, the total system loss with SVC is 17.563MW, 22.055MVAR Location X=X-Xc 0% 50% 80% 100% Table: 3 Results before and after placement of SVC Device for IEEE 30 bus system Bus Reactance Compensation (%) Similarly for 30 bus system the change in injected reactive power at 30 buses is 2 MVAR Without FACTS Voltage Phase angle pu degree 1.060 0.000 1.043 -5.497 1.022 -8.004 1.013 -9.661 1.028 -16.884 0.995 -18.015 Line losses Without SVC With SVC P MW Q MVAR P MW Q MVAR 0.16 -0.30 0.15 -0.285 0.03 -0.06 0.03 -0.060 Location Bus No 2 4 Power flows Without SVC With SVC PMW Q MVAR P MW Q MVAR 6.93 - 1.35 7.08 -0.46 3.67 -0.54 3.70 -0.21 Voltage pu Before After 1.000 1.000 0.984 0.988 Angle deg Before After -2.061 -2.030 -4.957 -4.879 Before TCPAR device Total loss: 6.122MW, 10.777 MVAR, after TCPAR placed total loss: 6.050 MW, -11.114 MVAR 423 International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013) Table: 7(a) Power flow without and with TCPAR Devices Location 2-4 Power Flows Before TCPAR P MW Q MVAR 27.7 -1.72 Table: 10(a) Power flow and line loss without and with TCSC Devices for IEEE 5 bus system After TCPAR P MW Q MVAR 29.5 -1.25 Table: 7(b) Line losses without and with TCPAR Devices for 5 bus system with r = 0.01; gamma = 10; alpha = 0.5 Line losess Before TCPAR P MW Q MVAR 0.46 -2.55 Location 2-4 After TCPAR P MW Q MVAR 0.52 -2.42 Table: 8. TCPAR is placed at 2-4 in IEEE 30 bus system Voltage pu Before After 1.043 1.043 1.013 1.015 Angle deg Before After -5.497 -5.497 -9.661 -9.462 Table: 9(a) Power flows without and with TCPAR for IEEE 30bus system with r = 0.01,gamma = 20, alpha=.5 Location 2-4 Power Flows Before TCPAR P MW Q MVAR 45.71 2.70 Location 2-4 0% -70% -50% -10% 10 20 0.176 0.054 0.027 0.0243 0.02674 0.032076 Power flows P Q MW MVAR 28.02 -8.96 44.27 -12.35 49.38 -18.60 49.90 -19.38 49.43 -18.67 48.40 -17.21 Line Losses P Q MW MVAR 0.50 -2.51 1.24 -2.80 1.62 -3.16 1.67 -3.22 1.63 -3.17 1.54 -3.08 Reactance Compensation (%) Reactance (Xline) 0% -70% -50% -10% 10 20 0.1703 0.0522 0.0261 0.0235 0.0258 0.0309 Power flows P Q MW MVAR 36.069 58.570 65.573 66.247 65.652 64.302 3.705 -6.946 -6.145 -7.416 -6.288 -14.000 Line Losses P Q MW MVAR 0.699 1.810 2.358 2.424 2.365 2.242 -1.812 -2.23 -2.80 -2.88 -2.81 -2.67 VI. CONCLUSIONS A simple and efficient load flow technique has been carried out for solving the IEEE 5 and IEEE 30 bus system. It is evident that the concept has fast convergence characteristics. It can be used for single line or multi lines compensation calculations without much extra computational burden. The work has been carried out by placing the deferent types of FACTS devices is placed in specified locations using in the test systems to minimize the power losses, improve the voltage profile, reduction in power losses and enhance the power transfer capabilities. After TCPAR P MW Q MVAR 48.67 6.67 Table: 9(b) Line losses without and with TCPAR for IEEE 30 bus system with r = 0.01,gamma = 20 ,alpha = 0.5 Line losess Before TCPAR P MW Q MVAR 1.10 -0.51 Reactance (Xline ) Table: 10(b) Power flow and loss without and with TCSC for 30 bus system Before TCPAR Total loss: 17.599 MW, 2.244MVAR After TCPAR Total loss: 17.309 MW, 21.119MVAR Bus No 2 4 Reactance Compensation (%) After TCPAR P MW Q MVAR 1.25 -0.10 REFERENCES From the above results it is evident that power flows is improved and loss is reduced in this technique. [1 ] P. Yan and A. Sekar,‖ Steady-state analysis of power system having multiple FACTS devices using line-flow-based equations‖, IEE Proc.-Gener. Transm. Distrib., Vol. 152, No. 1, January 2005 (3) Alternate method 4 (reactance compensation) In IEEE 30 bus system, TCSC is placed in Line: 2-4 Where reactance varies from -70% Xline to 20% Xline Devices XTCSC= rTCSC *Xline; Xline=Xold+XTCSC [2 ] Maheswarupu Sydulu,‖A new reliable and effective approach for adjustment of variable parameters of TCSC and TCPS in Load flow Studies‖, IEEE. pp.273-576,2004 [3 ] J.Baskaran, Dr.V.Palanisamy,‖Genetic Algorithm applied to optimal location of FACTS devices in a power system network considering economic saving cost‖. Vol.8,No.8, Nov 2004 TCSC is placed in IEEE 5 bus system in line 2 - 4 [4 ] Baghaee, H.R. Jannati, M. Vahidi, B. Hosseinian, S.H. Rastegar, H. Electr. Eng. Dept., ―Improvement of voltage stability and reduce power system losses by optimal allocation of multi-type FACTS devices‖,IEEE Trans.Power Systems, 2008 424 International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013) Author’s detail [5 ] F.D Galiana, K. Almeida, M. Toussaint, J. Griffin, and D.Atanackovic: ―Assessment and Control of the Impact of FACTS Devices on Power System Performance‖, IEEE Trans. Power Systems, Vol. 11, No. 4, Nov 1996. Mr. N. M. G. Kumar Currently pursuing P.hD at SVU College of engineering at Tirupati, AP, and India and obtained his B.E in Electrical and Electronics Engineering from Bangalore University at S.M.V.I.T.S., Bangalore. Obtained M.Tech (PSOC) at S.V.U.college engineering, Tirupati. Area of interest are power system planning, power system optimizations, power system reliability studies, Real time application of power system and like non-linear controllers applications to power systems. [6 ] N.G. Hingurani, L. Gyugyi, and Understanding FACTS: Concepts and Technology of Flexible AC Transmission Systems, IEEE Press, New York, 2000. [7 ] H.Saadat, ‖Power System Analysis‖, Tata McGraw-Hill Edition, 2001, pp.87-150. [8 ] J.A. Momoh, J. Zhu, G.D. Boswell, S. Hoffman, ―Power System Security Enhancement by OPF with Phase Shifter, ―IEEE Trans. on Power Systems, Vol. 16, No. 2, May 2001. [9 ] S.Sung-Hwan, L. Jung-UK, M. Seung-II, ―FACTS Operation Scheme for Enhancement of Power System Security,‖ in Proc of IEEE Power Tech Conference, Bologna, 2003, Vol. 3, pp. 36-41. P. Venkatesh currently working as Assistant Professor in Sri Vidyanikethan engineering college, Tirupati. Obtained his B.Tech in Electrical and Electronics Engineering from JNTU Hyderabad University at S.V.P.C.E, T. Putter. and Obtained his M.Tech in Electrical Power System from JNTU Anantapur University at Sri Vidyanikethan Engineering College, tirupati. Areas of interest are power system analysis, application of FACTS devices in Transmission systems. [10 ] J.G. Singh, S.N. Singh, S.C. Srivastava, ―Placement of FACTS Controllers for Enhancing Power System Loadability,‖ in Proc. of the IEEE Power India Conference, 2006, pp. 10-17. [11 ] S.N. Sing, A.K. David, ―A New Approach for Placement of FACTS Devices in Open Power Markets,‖ IEEE Power Engineering Review, 2001, Vol. 21, No. 9, pp. 58-60. [12 ] P. Kessel, H. Glavitsch, ―Estimating the Voltage Stability and Loadability of Power systems‖, IEEE Trans. on Power Delivery, 1986, Vol.1, pp.1586-1599. Dr. P. Sangameswara Raju is presently working as Professor in SVU College of Engineering, Tirupati. Obtained his Diploma and B.Tech in Electrical Engineering, M.Tech in power system operation and control and PhD in S.V. university, Tirupati. Areas of interest are power system operation, planning and application of fuzzy logic to power system, application of power system like non-linear controllers. [13 ] Nagrath, I.J., and Kothari, D.P., Power System Engineering, New Delhi, Tata McGraw-Hill Publishing Company Limited, 1995. [14 ] Saadat, Hadi, Power System Analysis, New Delhi, Tata McGrawHill Publishing Company Limited, 2002. [15 ] Wadhwa, C.L., Electrical Power Systems, New Delhi, New Age International publishers, 2005. [16 ] G.W. Stagg and A.H.El-Abiad. ―Computer Methods in Power System Analysis―. McGraw-Hill, Ist edition. 425