A.V.Naresh Babu and S.Sivanagaraju

Transcription

1 Internatonal Journal of Electroncs and Electrcal Engeerg Mult-Le Flexble Alternatg Current Transmsson System (FACTS) Controller for Transent Stablty Analyss of a Mult-Mache Power System Networ A.V.Naresh Babu and S.Svanagaraju Abstract A consderable progress has been acheved transent stablty analyss (TSA) wth varous FACTS controllers. But, all these controllers are assocated wth sgle transmsson le. Ths paper s tended to dscuss a new approach.e. a mult-le FACTS controller whch s terle power flow controller () for TSA of a mult-mache power system networ. A mathematcal model of, termed as power jecton model (PIM) presented and ths model s corporated Newton-Raphson (NR) power flow algorthm. Then, the reduced admttance matrx of a mult-mache power system networ for a three phase fault wthout and wth s obtaed whch s requred to draw the mache swg curves. A general approach based on L-dex has also been dscussed to fd the best locaton of to reduce the proxmty to stablty of a power system. Numercal results are carred out on two test systems namely, 6-bus and 11-bus systems. A program MATLAB has been wrtten to plot the varaton of generator rotor angle and speed dfference curves wthout and wth for TSA and also a smple approach has been presented to evaluate crtcal clearg tme for test systems. The results obtaed wthout and wth are compared and dscussed. Keywords Flexble alternatg current transmsson system (FACTS), frst swg stablty, terle power flow controller (), power jecton model (PIM). T I. INTRODUCTION HE recently developed converter based FACTS controllers are statc synchronous compensator (STATCOM), statc synchronous seres compensator (SSSC), unfed power flow controller (UPFC) and terle power flow controller (). All these FACTS controllers employ the voltage sourced converter as basc buldg bloc and plays vtal role power system stablty analyss, especally transent stablty analyss because of fast and relable control over the basc transmsson system parameters, such as voltage magntude, phase angle and le mpedance [1]. A.V.Naresh babu s wth DVR & Dr. HS MIC College of Technology, Kanchacherla , Andhra Pradesh, Inda (correspondg author phone: ; fax: ; e-mal: avnareshbabu@ gmal.com). S.Svanagaraju s wth Jawaharlal Nehru Technologcal Unversty, Kaada, Andhra Pradesh, Inda. (e-mal: srgr7@yahoo.co.). Transent stablty analyss s an mportant analyss the operaton and planng of power system networ [2]. The use of varous FACTS controllers for transent stablty analyss has been addressed [3]-[7]. The co-ordated exctaton and UPFC control to mprove power system transent stablty and voltage stablty has been reported [8]. Reference [9] presents a new control strategy, whch has superor performance compared to the conventonal control strategy for transent stablty mprovement the presence of advanced statc VAR compensators (ASVC). [1] Proposes a new control strategy of shunt FACTS devces to mprove the frst swg stablty lmt of smple power system whch provde sgnfcantly hgher stablty lmt than that of bangbang control (BBC). [11] Depcts the advantage of the use of thyrstor controlled seres compensator (TCSC) wth sutable controller over fxed capactor operaton for transent stablty mprovement of a mult-mache power system usg trajectory senstvty analyss. [12] Investgates the mpact of dfferent statc synchronous seres compensator (SSSC) control modes on small-sgnal and transent stablty of power system and t s concluded that the use of SSSC the constant mpedance emulaton mode s the most benefcal strategy to mprove both the small-sgnal and transent stablty. The optmal locaton of shunt FACTS controllers for transent stablty mprovement employg genetc algorthm has been presented [13]. The transent stablty constraed optmal power flow (TSOPF) s a bg challenge the feld of power system operaton because of ts computatonal complexty. The dfferent methods to fd the soluton for TSOPF problem has been dscussed [14]-[18]. Careful study of the former lterature reveals that the FACTS controllers used for transent stablty analyss s assocated wth sgle transmsson le. But, ths paper a mult-le FACTS controller whch s terle power flow controller () has been used for transent stablty analyss of mult-mache power system networ. Determaton of sutable locaton for the FACTS controllers s a typcal problem. In ths paper, the best locaton for the test system s obtaed based on L-dex. Generator rotor angle, rotor speed and fault clearg tme have been used to assess transent stablty marg of power system 19

2 Internatonal Journal of Electroncs and Electrcal Engeerg networ. The system loads are converted to constant admttances. The numercal results on the two test systems have demonstrated the feasblty and effectveness of the model for transent stablty analyss. The rest of the paper s organzed as follows: Secton II derves power jecton model of. Secton III descrbes the sutable locaton of. Secton IV gves overall soluton procedure. Secton V demonstrates the effectveness of model for transent stablty analyss through numercal examples and fally, conclusons are gven secton VI. Zse (n=j, ) s the seres couplg transformer mpedance. The jecton model s obtaed by replacg the voltage source ( Vse ) as current source ( Ise ) parallel wth the transmsson le. For the sae of smplcty, the resstance of the transmsson les and the seres couplg transformers are neglected. Therefore, the current source can be expressed as Ise = jbse Vse (1) II. MATHEMATICAL MODEL OF A. Operatg Prcple of In ts general form the ter le power flow controller employs a number of dc-to-ac converters each provdg seres compensaton for a dfferent le. In other words, the comprses a number of Statc Synchronous Seres Compensators (SSSC). The smplest consst of two bacto-bac dc-to-ac converters, whch are connected seres wth two transmsson les through seres couplg transformers and the dc termals of the converters are connected together va a common dc l as shown Fg.1.Wth ths, addton to provdg seres reactve compensaton, any converter can be controlled to supply real power to the common dc l from ts own transmsson le. Fg. 2 Equvalent crcut of two converter Now, the current source ( Ise ) can be modeled as jecton powers at the buses, j and. The complex power jected at th bus s S j, = V ( Ise ) (2) Substtute (1) (2) S j, = V n= j, n= j, ( jbse Vse ) (3) After smplfcaton, the actve power and reactve power jectons at th bus are Fg.1 Schematc dagram of two converter B. Mathematcal Model of In ths secton, a mathematcal model for whch wll be referred to as power jecton model s derved. Ths model s helpful understandg the mpact of the on the power system the steady state. Furthermore, the model can easly be corporated the power flow model. Usually, the steady state analyss of power systems, the VSC may be represented as a synchronous voltage source jectg an almost susodal voltage wth controllable magntude and angle. Based on ths, the equvalent crcut of s shown Fg.2[19]-[2]. In Fg.2, V, V j and V are the complex bus voltages at the buses, j and respectvely, defed as V = θ (m=, m V m j and ). Vse s the complex controllable seres jected voltage source, defed as Vse = Vse θse (n=j, ) and m Pj, = Re( Sj, ) = Q j n= j,, = Im( Sj, ) = ( V Vse bse s( θ θse ) (4) n= j, ( V Vse bse cos( θ θse ) () The complex power jected at n th bus (n=j,) s S Substtute (1) (6) S j, n = V n ( Ise ) (6) ( jbse Vse ) (7) j, n = V n After smplfcaton, the actve power and reactve power jectons at n th bus are P = Re( S j, n ) = V nvse bse s( θ θse j, n n ) (8) 11

3 Internatonal Journal of Electroncs and Electrcal Engeerg Q = Im( Sj, n ) = VnVsebse cos( θ θse j, n n Based on (4), (), (8), and (9), power jecton model of can be seen as three dependent power jectons at buses, j and as shown Fg.3. ) (9) where I, I G L and V G L V, represent complex current andvoltage vectors for generator and load buses. Y Y, Y Y are correspondg portons of the [ ], [ ] [ ] and [ ] GG GL LL LG networ Y-bus matrx. Eq. (13) can be rewrtten as V I L G Z = K LL GL F Y LG GG I V L G (14) Fg. 3 Power jecton model of two converter As nether absorbs nor jects actve power wth respect to the ac system, the actve power exchange between the converters va the dc l s zero,.e. ( Vse I + Vse I ) (1 ) Re = j j Where the superscrpt * denotes the conjugate of a complex number. If the resstances of seres transformers are neglected, (1) can be wrtten as Pj, m = (11) III. LOCATION OF m=, j, The transent and voltage stablty analyss plays an mportant role for system securty and relablty. One of the major recent research areas s the use of FACTS controllers for the co-ordaton between transent and voltage stablty analyss. So, ths paper, the voltage stablty dex (L-dex) has been used as the bass for selecton of sutable locatons of. If n s the total number of buses, g s the number of generator buses and j=g+1 to n are the load buses then the L- dces for gven load condtons are computed usg the load flow results for all the load buses wth the followg equaton [21]-[22]. g j = 1 V j L = 1 F j V (12) All the terms wth the sgma on the rght-hand sde of (12) are the complex quanttes. The values of F are obtaed from the networ Y-bus matrx. For the gven operatg condton, I Y Y V I G L = Y GG LG Y GL LL V G L j (13) 1 where [ FLG ] = [ YLL ] [ YLG ] and F j are the complex elements of [ F LG ] matrx. Among the varous dces for voltage stablty and voltage collapse predcton, the L-dex gves a scalar number to each load bus and farly consstent results. The advantage of ths method s the smplcty of the numercal calculaton and expressveness of the results. The L-dces for gven load condtons are computed for all load buses and the maxmum of the L- dces gves the proxmty of the system to voltage collapse. If the L-dces for load buses are close to (zero), dcatg that the system has maxmum stablty marg and close to 1(unty), dcatg that the system approaches to voltage collapse. IV. SOLUTION METHODOLOGY For clear reference, the overall soluton procedure for transent stablty analyss of mult-mache power system networ wth s summarzed as follows. Step 1: Input bus data, le data, generator data (transent reactance & erta constant) and data ( parameters and ts locaton). Step 2: Form the bus admttance matrx by specton method. Step 3: Obta power flow soluton by Newton-Raphson method. Step 4: Usg power flow soluton obtaed step 3, compute the ternal mache voltages and also replace all loads by constant shunt admttances. Step : Form the pre-fault, fault-on and post-fault reduced bus admttance matrces. Step 6: Evaluate the electrcal power output of each mache under fault and post-fault condtons. Step 7: Express mult mache equatons state varable form and also fd ts soluton durg fault and post fault condtons. Step 8: Plot the rotor angle dfference and speed dfference of each mache wth respect to slac bus for dfferent fault clearg tmes. Step 9: Repeat steps 2 to 8 wth. Step 1: Analyze whether system s stable or unstable based on the rotor angle dfference curves wth out and wth. The rotor angle dfference does not crease deftely, and then the system s found to be stable. Otherwse, t s unstable. Step 11: Repeat the evaluaton process for dfferent fault clearg tmes and predct crtcal fault clearg tme wth out and wth. 111

4 Internatonal Journal of Electroncs and Electrcal Engeerg V. RESULTS AND DISCUSSIONS In ths secton, numercal results are carred out on two standard test systems, 6-bus and11-bus systems [23] to demonstrate the effectveness and performance of for transent stablty analyss of mult-mache power system networ. In 6-bus test system, bus 1 s consdered as slac bus, whle bus 2 and 3 as generator buses and other buses are load buses. Smlarly, 11-bus system, bus 1 s consdered as slac bus, whle bus 1 and 11 as generator buses and other buses are load buses. For the test systems, the convergence tolerance s 1e- p.u. System base MVA s 1. At frst, the pre-fault power flow soluton for the two test systems obtaed usg standard NR method. The obtaed results are compared wth the soluton gven example 11.7 [23] and observed that the results are exactly matched. Next, the pre-fault power flow soluton for the two test systems obtaed wth. The prefault power flow solutons for two test systems wthout and wth are gven Table 1 and Table 2 respectvely. The pre-fault power flow results are requred for transent stablty analyss. Further, from Table 1 and Table 2, t s clear that the voltages at slac bus and generator buses are same but there s a sgnfcant change load bus voltages wth. Especally, the voltage at bus-6 of 6-bus system and the voltage at bus-9 of 11-bus system creased to whch converters are connected. The sutable locaton of s obtaed based on L-dex crteron. In ths, the L-dces are computed for all load buses of test system and rang s gven. The maxmum of L-dex gves the proxmty of the system to voltage collapse and raned as 1(one). So, placed near to frst raned bus to avod voltage collapse. The L-dces for the two test systems are gven Table 3 and Table 4 respectvely. For 6-bus system, the L-dex s more for bus 6. Therefore, one converter of s embedded a le between the buses 1-6 whch s consdered as 1 st le and the other converter of s placed a le between the buses 4-6 whch s consdered as 2 nd le and bus 6 s selected as common bus for two converters. Smlarly, for 11-bus system, the L-dex s more for bus 9. Therefore, one converter of s embedded a le between the buses 4-9 whch s consdered as 1 st le and the other converter of s placed a le between the buses 8-9 whch s consdered as 2 nd le and bus 9 s selected as common bus for two converters. The locaton and ts parameters for the two test systems are gven Table. Fally, the system s examed stable or unstable from the swg curves. A sold three-phase fault s assumed at a bus the power system networ. A fault a power system can be ether of self-clearg type or t s cleared by le solaton. In ths manuscrpt, t s consdered that the fault s cleared by le solaton. Usually, the slac bus s selected as the reference and the phase angle dfference of all other generators wth respect to the reference mache are plotted. Generally, the soluton s carred out for two swgs to show that the second swg s not greater than the frst one. If the angle dfferences do not crease, the system s stable and f any of the angle dfferences crease deftely, the system s unstable. Typcally, the fault should be cleared as early as possble so that damage on the system can be avoded to a large extent. In ths paper, the fault clearg tme s creased gradually to fd crtcal clearg tme. The swg curves and rotor speed dfference curves of the two test systems for dfferent fault clearg tmes are shown Fg.4 to Fg.11. For 6-bus system, t s assumed that a threephase fault occurs on le -6 near bus 6. The varaton of generator-2 rotor angle dfference wthout and wth for dfferent fault clearg tmes s shown Fg.4. From Fg. 4, t s observed that the varaton of generator-2 rotor angle dfference do not crease deftely wthout and wth for fault clearg tme (t c ) =.4 sec, therefore the system s found to be stable. From Fg. 4, t s seen that the varaton of generator-2 rotor angle dfference creases deftely wthout, therefore the system s found to be unstable when the fault s cleared. sec. But, the varaton of generator-2 rotor angle dfference do not creases deftely wth, therefore the system s found to be stable for the same fault clearg tme. Therefore, t can be concluded that the fault clearg tme s creased because of the system, whch dcates the mprovement of transent stablty marg of the system. From Fg. 4, t s also observed that the varaton of generator-2 rotor angle dfference do not crease deftely wthout, therefore the system s found to be crtcally stable when the fault s cleared.4 sec whch s near to unstable pot. Further, t can be concluded that the crtcal clearg tme (t cc ) for 6-bus system wthout s between.4 to. sec.but the t cc s creased wth whch s greater than. sec. The varaton of generator-2 rotor speed dfference wthout and wth for dfferent fault clearg tmes s shown Fg. and t s wth the lmts for t c =.4 & t c =.4 sec wthout and wth as shown Fg. and respectvely. But, rotor speed dfference creases deftely wthout and t s wth the lmts wth when the fault s cleared at t c =. as shown Fg.. For the sae of completeness, the varaton of generator-3 rotor angle dfference and speed dfference wthout and wth for the same fault clearg tmes are shown Fg.6 and Fg.7 respectvely. In addton, the same analyss has been carred out for 11- bus system and t s assumed that a three-phase fault occurs on le 3-4 near bus 4. The varaton of generator-1 rotor angle dfference and speed dfference wthout and wth for dfferent fault clearg tmes s shown Fg.8 and Fg.9 respectvely. For 11-bus system also, Fg.8 shows that the mproves the system stablty, whch was otherwse unstable when the fault s cleared.7 sec. For the sae of completeness, the varaton of generator-11 rotor angle dfference and speed dfference wthout and wth for same fault clearg tmes s shown Fg.1 and Fg.11 respectvely. Table 6 summarzes the graphcal results of 11- bus system along wth 6-bus system. 112

5 Internatonal Journal of Electroncs and Electrcal Engeerg Bus No. Magntude of Voltages (p.u) Wthout TABLE I THE PRE FUALT POWER FLOW RESULTS OF 6-BUS SYSTEM WITH OUT AND WITH Wth Angle of Voltages (deg.) Wthout Wth Actve Power Generaton (MW) Wthout Wth Reactve Power Generaton (MVAR) Wthout Wth Bus No. TABLE I I THE PRE FUALT POWER FLOW RESULTS OF 11-BUS SYSTEM WITH OUT AND WITH Magntude of Voltages (p.u) Wthout Wth Angle of Voltages (deg.) Wthout Wth Actve Power Generaton (MW) Wthout Wth Reactve Power Generaton (MVAR) Wthout Wth TABLE III L-INDICES OF 6-BUS SYSTEM Bus No. L-Index Ran TABLE IV L-INDICES OF 11-BUS SYSTEM Bus No. L-Index Ran

6 Internatonal Journal of Electroncs and Electrcal Engeerg Wth 2 1 Wth Wth 4 3 Wth Wth Wth Fg. 4 Varaton of generator 2(6 bus system) rotor angle dfference wthout and wth for dfferent fault clearg tmes(t c ), t c =.4 t c =. t c =.4 Fg. Varaton of generator 2(6 bus system) rotor speed dfference wthout and wth for dfferent fault clearg tmes(t c ), t c =.4 t c =. t c =.4 114

7 Internatonal Journal of Electroncs and Electrcal Engeerg Wth ) 1 1 Wth ) Wth ) Wth ) Wth Wth Fg. 6 Varaton of generator 3(6 bus system) rotor angle dfference wthout and wth for dfferent fault clearg tmes(t c ), t c =.4 t c =. t c =.4 Fg. 7 Varaton of generator 3(6 bus system) rotor speed dfference wthout and wth for dfferent fault clearg tmes(t c ), t c =.4 t c =. t c =.4 11

8 Internatonal Journal of Electroncs and Electrcal Engeerg Wth 2 1 Wth Wth 2 Wth Wth 2 1 Wth Fg. 8 Varaton of generator 1(11 bus system) rotor angle dfference wthout and wth for dfferent fault clearg tmes(t c ), t c =.6 t c =.7 t c =.7 Fg. 9 Varaton of generator 1(11 bus system) rotor speed dfference wthout and wth for dfferent fault clearg tmes(t c ), t c =.6 t c =.7 t c =.7 116

9 Internatonal Journal of Electroncs and Electrcal Engeerg Wth 2. 2 Wth Wth 2 1. Wth Wth 2 1. Wth Fg. 1 Varaton of generator 11(11 bus system) rotor angle dfference wthout and wth for dfferent fault clearg tmes(t c ), t c =.6 t c =.7 t c =.7 Fg. 11 Varaton of generator 11(11 bus system) rotor speed dfference wthout and wth for dfferent fault clearg tmes(t c ), t c =.6 t c =.7 t c =.7 117

10 Internatonal Journal of Electroncs and Electrcal Engeerg Test system TABLE V LOCATION AND PARAMETERS Locaton Parameters Bus Les Vse (p.u) θse (deg) No. 6 - bus & bus & Test system Faulted bus TABLE VI STATUS OF TEST SYSTEMS WITH OUT AND WITH FOR DIFFERENT FAULT CLEARING TIMES Le removed to clear fault Fault clearg tme, t c (sec.) Status of system wthout wth Crtcal clearg tme, t cc (sec.) wthout wth 6- bus 11- bus stable stable.4 crtcally stable stable. unstable stable.6 stable stable.7 crtcally stable.7 unstable stable.4 t cc <...7 t cc <.7 stable.7 VI. CONCLUSION In ths paper, a mult-le flexble alternatg current transmsson system (FACTS) controller whch s terle power flow controller () has been addressed. The power jecton model of along wth Newton-Raphson (NR) power flow soluton method has been used to plot swg curves for transent stablty analyss of a mult-mache power system networ. Numercal results on the test systems have demonstrated the feasblty and effectveness of the model. The placement of the, based on L-dex s found to be benefcal for system stablty. It s shown that, there s an crease load bus voltages to whch converters are connected and the pea of frst swg of the swg curve can be reduced sgnfcantly wth for both the test systems. Further, a system wthout becomes unstable when the fault duraton exceeds the crtcal clearg tme. However, the sutable locaton wth chosen parameters may help the system to rema stable even under those condtons.e. the fault clearg tme s creased wth whch dcates the mprovement of transent stablty marg of the system. The strong mult-le control capablty of plays an mportant role power systems and s also a useful tool for planng, operaton and control of power systems. REFERENCES [1] N.G.Hgoran and L.Gyugy, Understandg FACTS-Concepts and Technology of Flexble AC Transmsson Systems, IEEE press, Frst Indan Edton, 21. [2] P.Kundur, Power System Stablty and Control, McGraw Hll, [3] R.Mhalc,P.Zuno and D.Povh, Improvement of transent stablty usg unfed power flow controller, IEEE Trans. Power Del., vol.11, no.1, pp , Jan [4] U.Gabrjel and R.Mhalc, Drect methods for transent stablty assessment power systems comprsg controllable seres devces, IEEE Trans. Power Syst., vol.17, no.4, pp , Nov.22. [] R.Mhalc and U.Gabrjel, A structure-preservg energy functon for a statc seres synchronous compensator, IEEE Trans. Power Syst., vol.19, no.3, pp.11-17, Aug.24. [6] V.Azbe,U.Gabrjel, D.Povh and R.Mhalc, The energy functon of a general multmache system wth a unfed power flow controller, IEEE Trans. Power Syst., vol.2, no.3, pp , Aug.2. [7] Haque M.H., Effects of exact le model and shunt FACTS devces on frst swg stablty lmt, Int. J. Power Energy Syst., vol.2, no.2, pp , 2. [8] H.Chen,Y.Wang and R.Zhou, Transent and voltage stablty enhancement va co-ordated exctaton and UPFC control, IEE Proc.- Gener.Transm.Dstrb., vol.148, no.3, pp.21-28, May 21. [9] S.Abazar, J.Mahdav,H.Mohtar and A.Emad, Transent stablty mprovement by usg advanced statc VAR compensators, Electrc Power Components and Syatems,vol.31,pp ,23. [1] M.H.Haque, Improvement of frst swg stablty lmt by utlzg full beneft of shunt FACTS devces, IEEE Trans. Power Syst., vol.19, no.4, pp , Nov. 24. [11] Dheeman Chatterjee and Ardam Ghosh, TCSC control desgn for transent stablty mprovement of a mult-mache power system usg trajectory senstvty, Electrcal. Power Systems Research, vol. 77, pp , 27. [12] M.S.Castro,H.M.Ayres,V.F.da Costa and L.C.P.da slva, Impacts of the SSSC control mode on small-sgnal and transent stablty of a power system, Electrc Power Systems Research, vol. 77, pp. 1-9, 27. [13] S.Panda and R.N.Patel, Optmal locaton of shunt FACTS controllers for transent stablty mprovement employg genetc algorthm, 118

11 Internatonal Journal of Electroncs and Electrcal Engeerg Electrc Power Components and Systems, vol.3, no.2,pp , 27. [14] N.Mo,Z.Y.Zou,K.W Chan and T.Y.G.Pong, Transent stablty constraed optmal power flow usg partcle swarm optmsaton, IET Gener.Transm.Dstrb., vol.1, no.3,pp , May 27. [1] H.R.Ca,C.Y.chung and K.P Wong, Applcaton of dfferental evoluton algorthm for transent stablty constraed optmal power flow, IEEE Trans. Power Systems, vol.23, no.2, pp , May 28. [16] Le Chen,Yong M,Fe Xu and Ka-Peng Wang, A Contuaton based method to compute the relevant unstable equlbrum pots for power system transent stablty analyss, IEEE Trans. Power Systems, vol.24, no.1, pp , Feb. 29. [17] Quanyuan Jang and Guangchao Geng, A Reduced space teror pot method for transent stablty constraed optmal power flow, IEEE Trans. Power Systems, vol.2, no.3, pp , Aug. 21. [18] Quanyuan Jang and Zhguang Huang, An enhanced numercal dscretzaton method for transent stablty constraed optmal power flow, IEEE Trans. Power Systems, vol.2, no.4, pp , Nov. 21. [19] A.V.Naresh Babu, S.Svanagaraju, Ch.Padmanabharaju and T.Ramana Power flow analyss of a power system the presence of terle power flow controller(), ARPN Journal of Engeerg and Appled Scences, vol., no.1,pp.1-4, Oct. 21. [2] A.V.Naresh Babu and S.Svanagaraju, Mathematcal modellg,analyss and effects of terle power flow controller() parameters power flow studes, 4 th IEEE- Inda Int. Conf. on Power Electroncs, New Delh, Inda, Jan [21] D.Thuaram and A.Lom, Selecton of statc VAR compensator locaton and sze for system voltage stablty mprovement, Electrc Power Systems Research, vol. 4, pp , 2. [22] D.Thuaram, L.Jens and K.Vsaha, Improvement of system securty wth unfed power flow controller at sutable locatons under networ contgences of terconnected systems, IEE Proc.- Gener.Transm.Dstrb., vol.12, no., pp , Sep.2. [23] H.Saadat, Power System Analyss, Tata McGraw-Hll Edton, 22. A.V.Naresh Babu receved hs B.Tech electrcal and electroncs engeerg from RVR&JC CE, Andhra Pradesh, Inda, 23 and M.Tech power systems from Jawaharlal Nehru Technologcal Unversty- Kaada, Andhra Pradesh, Inda, 27.He s currently pursug Ph.D from the department of electrcal & electroncs engeerg, Jawaharlal Nehru Technologcal Unversty-Kaada. He s presently Assocate Professor the department of electrcal and electroncs engeerg at DVR &Dr. HS MIC College of Technology. Hs research terests clude FACTS technology, power electroncs applcatons to power systems and Optmzaton Technques. S.Svanagaraju receved hs B.Tech electrcal and electroncs engeerg from Andhra Unversty, Andhra Pradesh, Inda 1998, M.Tech electrcal power systems from Indan Insttute of Technology (IIT), Khargpur, West Bengal, Inda 2 and Ph.D Electrcal and Electroncs Engeerg from Jawaharlal Nehru Technologcal Unversty-Hyderabad, AndhraPradesh, Inda 24.Dr.S.Svanagaraju s currently Assocate Professor the department of electrcal engeerg at Jawaharlal Nehru Technologcal Unversty-Kaada. He receved two Natonal awards (Pandt Madan Mohan Malavya memoral prze award and best paper prze award) from the Insttute of Engeers(Inda) for the year Hs research terests clude FACTS technology, Dstrbuton Systems automaton and genetc algorthm applcatons to Power Systems. 119