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International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.

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  1. 1. Kusum Arora, Dr. S.K. Agarwal, Dr. Narendra Kumar, Dharam Vir / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.821-826821 | P a g eAnalysis of Power Flow Control in Power System Model usingThyristor Controlled Series Capacitor (TCSC)Kusum Arora*, Dr. S.K. Agarwal **, Dr. Narendra Kumar ***, DharamVir*****(Department of Electronics Engineering, YMCA University of Science & Technology, Faridabad, India)** (Department of Electronics Engineering, YMCA University of Science & Technology, Faridabad, India)*** (Department of Electrical Engineering, Delhi College of Engineering, and New Delhi, India)**** (Department of Electronics Engg, YMCA University of Science & Technology, Faridabad, India)ABSTRACTThe characteristic of a thyristorcontrolled series compensator (TCSC) is usuallydefined by the overall reactance of the deviceversus the firing angle of the TCR that isconnected in parallel with a fixed capacitor. Werepresents a model control circuit by usingmicrocontroller to generate trigger pulses to firethe gate of the thyristors according to the setfiring angle for required output. It brings out theoperation of TCSC along with numericalequations. It also gives impedance characteristicscurve of a TCSC device and specifies the rangeof inductance and capacitance region and alsofinds a suitable value of inductance andcapacitance. We analyze the different waveformsin the capacitive as well as inductive region ofTCSC, optimal setting of TCSC is determinedthrough the software code written in MATLAB.Keywords - Firing angle, Thyristor ControlledSeries Compensator (TCSC), Optimal Power Flow,Power system analysis, Zero Crossing DetectorI. INTRODUCTIONModern electric power utilities are facingmany challenges due to ever-increasing complexityin their operation and structure. In the recent past,one of the problems that got wide attention is thepower system instabilities. With the lack of newgeneration and transmission facilities and overexploitation of the existing facilities make thesetypes of problems more imminent in modern powersystems. With the increased loading oftransmission lines, the problem of transient stabilityafter a major fault can become a transmissionpower limiting factor. The use of fixed capacitorsto improve transient stability is well known.However, fixed capacitors in series with thetransmission lines may cause sub synchronousresonance that can lead to electrical instability atoscillation frequencies lower than the normalsystem frequency. So there exists the need forswitched series capacitors [1]. The switchingsequences are determined, based on the signreversal of a decision function, which is derivedfrom the equal-area criterion and requiresknowledge of the final steady state. This method isvery complicated and later in the author himselfadopted a far simpler and more practical controlapproach .The control law adopted was to insertand bypass a series capacitor based on the speeddeviation. At the time the above ideas in and wereproposed, dynamically varying series compensationcould only be achieved using capacitor banksswitched in and out with mechanical circuitbreakers; however such devices were in practicetoo slow and unreliable for high speed use. Sothese ideas remained on hold for nearly twodecades until the evolution of FACTS devices.Flexible AC transmission System (FACTS)controllers use thyristor switching devices toprovide greater control, speed and flexibility of actransmission systems [2]. The Thyristor ControlledSeries Compensator (TCSC) is a second generationFACTS controller capable of providing fastvariable compensation. This paper focuses on thevariable impedance capability of TCSC forenhancing the transient stability. It Mitigate subsynchronous resonance ,Increase power transfer,Optimize power flow between the lines, Reducesystem losses, Increase transient stability, Increasedynamic stability, Control current, Reducedamping oscillations, Increase voltage stability,Fault current limiting [1] [3]. There exists a class ofcontrol schemes for transient stability enhancementusing TCSC. In this paper, transient stabilitycontrol model scheme, namely: microcontrollerbased control is done for study. The controller is asimple speed deviation based controller and canprovide a drastic improvement in transient stability.In addition to the transient stability enhancement,this controller provides power oscillation dampingalso. We calculate the various resonance points inthe impedance characteristics of the TCSC withrespect to various firing angle. We analyses anddesign the TCSC model using ORCAD andMATLAB. The rest of the paper as follows.Section II Literature Survey, Section III Benefits ofTCSC, Section IV modeling of the TCSC, Section
  2. 2. Kusum Arora, Dr. S.K. Agarwal, Dr. Narendra Kumar, Dharam Vir / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.821-826822 | P a g eV Analysis of steady state transient behavior theimplemented TCSC circuit and finally conclusionand future work in section VI.II. LITERATURE SURVEYThe Equation of reactive power impliesthat impedance of series compensating capacitorcancels the portion of the actual line reactance &thereby effective transmission impedance isreduced.222)1()1(2kCOSkVXIQ CAs if the line was physically shortened orwe can say that in order to increase the current inthe given circuit series impedance of the actualphysical line, the voltage across this impedancemust be increased. This can be accomplished by anappropriate series connected circuit element such ascapacitor, the impedance of which produces avoltage opposite to the prevailing voltage acrossthe series line reactance and thus causing latervoltage to increase .So Series compensatorprovides desired series compensation voltage whenand where required if installed [4] [5].According to S.Meikandasivam, RajeshKumar Nima and Shailendra Kumar Jain in theirpaper “Beaviour Study 0f TCSC presented inWorld Academy of Science Engineering andtechnology 45 2008” World‟s first 3 phase [5], 2 X165 MVAR, TCSC was installed in 1992 inKayenta substation, Arizona. It raised thetransmission capacity of transmission line by 30%,but it was soon realized that the device is also avery effective means for providing damping ofelectromechanical power oscillations. A thirdpossible application of TCSC emerged from theonsite observations that it can provide seriescompensation without causing the same risk forsub-synchronous resonance (SSR) a fixed seriescapacitor. World‟s first TCSC for subsynchronousresonance (SSR) mitigation was installed in Stode,Sweden in 1998, by ABB. Specifically this periodmakes a valiant period for TCSC and makes theresearchers to turn on to TCSC And while selectinginductance, XL should be sufficiently smaller thanthat of the capacitor XC to get both effectiveinductive and capacitive reactance across thedevice. Also XL should not be equal to XC value; orelse a resonance develops that result in infiniteimpedance an unacceptable condition. Note thatwhile varying XL (α), a condition should not allowto occur XL (α) = XC.Hailian Xie and Lennart Angquistdesigned a new control scheme instead oftraditional firing angle control scheme called as theStatic Voltage Reversal Control scheme. Followingthat scheme the simulation results are analyzedusing real time simulator.T.Venegas and C.R. Fuerete Esquivelreport on large scale power flow studies. The ASCmodel are developed in phase coordinates andincorporated into an existing Newton Raphsonpower flow algorithm and analysis is done on bothbalanced and unbalanced power network operatingconditions.Dragan Jovcic, member IEEE andG.N.Pillai presents an analytical, linear, state-spacemodel of TCSC. First a simplified fundamentalfrequency model of TCSC is proposed and themodel results are verified. Using the nonlinearTCSC segment, a simplified nonlinear state spacemodel is derived where frequency of dominantTCSC complex poles shows linear dependence onthe firing angle. The nonlinear element is linearizedand linked with the AC network model along withTCSC model and is implemented on MATLAB andverified on EMTDC/ PSCAD in frequency andTime domain for a range of operating conditions.III. OPERATION AND ADVANTAGES OFVARIOUS MODES OF OPERATION, ANDBENEFITS OF TCSCA. CONCEPT OF TCSC:Concept behind TCSC is to decrease orincrease overall effective series transmissionimpedance from sending end to the receiving endso as to control the transmission of power and thecurrent in the reactor can be controlled from zero tomaximum by the method of firing delay angle.Closure of the thyristor valve is delayed w.r.t. peakof the applied voltage in each half cycle thusduration of the current conduction interval iscontrolled [6].Figure 1. Various ware form shows the operationof thyristor with various firing and conductionangles.There are three modes of operation of TCSCdepending upon the firing angle of the pulses fed tothe thyristor. Thyristor blocked mode Thyristor bypassed mode Vernier operating modeB. Thyristor blocked Operating Mode:When the thyristor valve is not triggered and the
  3. 3. Kusum Arora, Dr. S.K. Agarwal, Dr. Narendra Kumar, Dharam Vir / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.821-826823 | P a g eTCSC is operating in blocking mode. In this mode,the TCSC performs like a fixed series capacitorC. Thyristor bypass Operating mode:In bypass mode the thyristor valve istriggered continuously and the valve staysconducting all the time; so the TCSC behaves like aparallel connection of the series capacitor with theinductor, Ls in the thyristor valve branch. In thismode, the resulting voltage in the steady stateacross the TCSC is inductive and the valve currentis somewhat bigger than the line current due to thecurrent generation in the capacitor bank. Forpractical TCSC‟s with ratio (XL/XC) between 0.1 to0.3 ranges, the capacitor voltage at a given linecurrent is much lower in bypass than in blockingmode. Therefore, the bypass mode is utilized as ameans to reduce the capacitor stress during faults[7] [9].D. Vernier Operating Mode:In Vernier control the TCSC dynamics arevaried continuously by controlling the firing angle.The firing angle is possible from 0oto 90ofor eachhalf cycle when it is generated from the zerocrossing of the line current hence divided into twoparts:Figure 2. Equivalent circuit of TCSC in VernierMode1) Capacitive Boost mode:In capacitive boost mode a trigger pulse issupplied to the thyristor having forward voltagejust before the capacitor voltage crosses the zeroline, so a capacitor discharge current pulse willcirculate through the parallel inductive branch. Thedischarge current pulse adds to the line currentthrough the capacitor and causes a capacitorvoltage that adds to the voltage caused by the linecurrent. The capacitor peak voltage thus will beincreased in proportion to the charge that passesthrough the thyristor branch. The fundamentalvoltage also increases almost proportionally to thecharge. From the system point of view, this modeinserts capacitors to the line up to nearly threetimes the fixed capacitor. This is the normaloperating mode of TCSC [8] [15].2) Inductive Boost Mode:In inductive boost mode the circulatingcurrent in the TCSC thyristor branch is bigger thanthe line current. In this mode, large thyristorcurrents result and further the capacitor voltagewaveform is very much distorted from itssinusoidal shape. The peak voltage appears close tothe turn on. The poor waveform and the high valvestress make the inductive boost mode less attractivefor steady state operation [8].E. ADVANTAGES OF FACTS DEVICES INAC SYSTEMS:Table 1: Advantage of FACTS devices in ACSystemsFACTSDEVICEPowerFlowVoltageControlTransientStabilityOscillationDampingSVC * *** * **STATCOM * *** ** **TCSC ** * *** **SSSC *** * *** **UPFC *** *** *** ***Influence: * Small, ** Medium, *** StrongThere are various types of FACT controllers in themarket having their own advantages dependingupon their individual characteristics .Herecomparison study has been done on different FACTcontrollers to study their impact on variousapplication, Table 1 shows the overall advantagesof FACT devices in AC systems [10] [16].IV. MODELING OF THE TCSCThe circuit is modeled using Simulink inMATLAB and ORCAD. It uses the Simulinkenvironment, allowing user to build a model usingsimple click and drag procedures. It can help drawthe circuit topology rapidly, and can help in theanalysis the circuit and its interactions withmechanical, thermal, control, and other disciplines.This is possible because all the electrical parts ofthe simulation interact with the extensive Simulinkmodeling library. Since Simulink uses MATLABas its computational engine, we can also useMATLAB toolboxes and Simulink block sets. Herein mat lab various blocks like voltage generator,series RLC circuit block, series RLC load branchblock, current meter, voltage meter, scopes to viewvarious signals, power meter block, thyristor block,demultiplexer bus block all are interconnected tomake an open loop TCSC Simulink model which isconnected in series with the single sourcetransmission line [14].Figure 5. TCSC Circuit for simulationFor analyzing the thyristor, capacitorcurrent and capacitor voltage, firing pulses aregiven to the circuit through pulse generator. Toanalyze the circuit in capacitive mode andinductive mode of TCSC, the pulse to be applied
  4. 4. Kusum Arora, Dr. S.K. Agarwal, Dr. Narendra Kumar, Dharam Vir / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.821-826824 | P a g eare in region of Vernier capacitive which lies in160oto 180oand 90oto 135oi.e. the delay of 8.8msto 10ms and 5ms to 7.5ms respectively [11]. Thisgives the analysis of waveform of capacitorvoltage, line current, thyristor current and capacitorcurrent of TCSC as shown in fig.. It has beenconcluded that at if alpha=117ofor positivewaveform then there should be a difference orphase delay of 180ofor the negative waveform thenonly thyristor will fire at the same interval andhence the conduction time will be equal and o/pwill be symmetrical [12]. In practical applications,a lookup table method is used to describe thisrelationship. When the desired value of reactanceXtcsc is determined from the power system state, therequired value of the firing angle is obtained fromthe table which shows the reactance step responseof the TCSC to demanded change in from 1 p.u. to2.1p.u., corresponding to a change in firing anglefrom to 175oto151o. It can be seen from scopeoutput that more than 200 ms is needed for thefundamental frequency reactance to reach its newsteady-state value [13].Figure 6. Simulink Model of TCSCV. ANALYSIS OF STEADY STATE TRANSIENTBEHAVIOR THE IMPLEMENTED TCSCTransient response of TCSC is analyzed byincreasing the simulation time. The response gotstable after few seconds of the firing as shownbelow.Figure 7. I/P voltage & o/p pulses of pulsegenerators.Figure 8. Output voltage a delay of 8.5ms.Figure 9. Out put voltage at delay of 5.5 msFigure 10. Voltage across TCSC at delay of 8.5msFigure 11. Fourier Transform of the O/P voltage.Figure 12. Fourier Transform at delay=5.5 msA. Resultant Conclusion of TCSC modelingThree main signals of the TCSC (linecurrent), thyristor current (It) and capacitor voltage(Vc) the first one with a firing angle=16º and the2nd one with firing angle=50º. The TCSC can beused to modify the power transfer on transmissionlines because it is able to experience a fast responsewhen the firing angle is controlled appropriately. Ifthe transient period lasts for a long time the systemmay turn eventually unstable. Another noteworthypoint is the fact that the signals‟ amplitude in thetransient period remains within proper limits. Thisis important because if the amplitude goes too high,the components may be damaged.Figure13. Response when firing angle is 16o.Figure14. Response when firing angle is 50o.Fig.14. System response with firing angle = 42o
  5. 5. Kusum Arora, Dr. S.K. Agarwal, Dr. Narendra Kumar, Dharam Vir / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.821-826825 | P a g eVI. CONCLUSIONThe TCSC can be operated in capacitiveand an inductive mode is rarely used in practice.The FACTS controller with its classification andperformance of TCSC are included in this paper.The advantages of FACTS devices and variousoperating modes of TCSC are specified. This paperwork can be extended in future for TCSC modelingwith a number of bus system and determine themethod for controlling the power flow. Alinearized discrete-time model of a TCSC-compensated transmission line is presented in thispaper. The model derived considers the propercharacteristic of TCSC, the variation in itsimpedance with the firing angle of the TCR. Eventhough the line capacitance effects are neglected,they can be incorporated in the state equationwithout any major change in the model derivation,apart from an increase in the size of the matrices.The model derived is validated through digitalcomputer simulation studies. It is shown that theeigen values of a TCSC-compensated transmissionline has two complex conjugate pairs of poleswhose real parts depend only on the line resistanceand reactance. This model has shown thedisturbances very accurately. Three differentcontrollers are designed, based on this linearizedmodel, which requires the measurements of localvariables only. The performance of the proposedcontrollers under various disturbances arecompared and analyzed.Similarly in future implementation couldbe of a three-phase device as well as the simulationto series compensation may be by voltage sourcedconverters It can also be implemented with Neuroand fuzzy logic or some different strategies maynow be developed to control the reactance of theTCSC through firing angle adjustments. In order toverify the performance of control strategies inactual operating conditions new techniques likeinstead of inductive load an original load could beimplied.REFERENCES[1] N.G. Hingorani and L. Gyugyi“Understanding FACTS Concept andTechnology of Flexible AC TransmissionSystems”,IEEE.[2] Caudio A, Zeno & T.Faur, Canada –“Analysis of SVC and TCSC Controllersin Voltage Collappse” IEEE Trans. PowerSystems, Vol: 14, 1st Februrary 1999 pp158-165.[3] Preeti Singh, Mrs.Lini Mathew,Prof.S.Chatterji, NITTTR, Chandigarh“Matlab based Simulation of TCSCFACTS Controller”- 2NDNationalConference on Challenges &Opportunities in Information Technology(COIT-2008) - March 2008.[4] Hailian Xie, Lennart Angquist, StudentRoyal Institute of Technology, StockholmON “Synchronous Voltage Reversalcontrol of TCSC – Impact on SSRConditions‟.[5] T.Venegas,C.R.Fuerte-Esquivel ON“Steady State Modeling of an AdvancedSeries Compensator for Power FlowAnalysis of Electric Networks in PhaseCo-ordinates” IEEE Transactions onPower Delivery , Vol.16,No.4, October2001.[6] Mojtaba Khederzadeh and TarlochanSingh Sidhu, Fellow IEEE ON “Impact ofTCSC on the Protection of TransmissionLines” – IEEE Transactions on PowerDelivery, Vol:21, No:1, January 2006.[7] R. M Mathur and R. K. Verma, Thyristor-based FACTS Controllers for ElectricalTransmission Systems, IEEE press,Piscataway, 2002.[8] Othman HA, Ongquist L. Analyticalmodeling of thyristor-controlled seriescapacitor for ssr studies. Tran IEEEPower Syst 1996; 11:1–10.[9] Rajaraman R, Dobson I, Lasseter RH,Shern Y. Computing the damping ofsubsynchronous oscillations due to athyristor-controlled series capacitor. IEEETrans Power Delivery 1996; 11(2):1120–1126.[10] H.G. Han, J.K. Park, B.H. Lee, Analysisof thyristor controlled series compensatordynamics using the state variableapproach of a periodic system model,IEEE Trans. Power Deliver. 12 (4) (1997)1744–1750.[11] A.D. Del Rosso, C.A. Canizares, V.M.Dona, A study of TCSC controller designfor power system stability improvement,IEEE Trans. Power Syst. 18 (4) (2003)1487–1496.[12] P. Mattavelli, G.C. Verghese, A.M.Stankovitctt, Phasor dynamics ofthyristor-controlled series capacitorsystems, IEEE Trans. Power Syst. 12 (3)(1997) 1259–1267.[13] B.H. Li, Q.H. Wu, D.R. Turner, P.Y.Wang, X.X. Zhou, Modeling of TCSCdynamics for control and analysis ofpower system stability, Int. J. Elec. PowerEnergy. Syst. 22 (1) (2000) 43–49.[14] S.Meikandasivam, Rajesh Kumar Nemaand Shailendra Kumar Jain,“Behavioralstudy of TCSC device AMATLAB/Simulink implementation”,International Journal of Electronics andElectrical Engineering, vol. 2, no. 10, Oct.2011, pp. 151– 161
  6. 6. Kusum Arora, Dr. S.K. Agarwal, Dr. Narendra Kumar, Dharam Vir / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.821-826826 | P a g e[15] Venu Yarlagadda, Dr. B.V Sankar Ramand Dr. K. R. M Rao, “Automatic Controlof Thyristor Controlled Series Capacitor(TCSC)”, Vol. 2, Issue 3, May-Jun 2012,pp. 444-449.[16] Ying Xiao, Y.H. Song and Y.Z. Sun,“Power flow Control approach to powersystems with embedded FACTS devices”,IEEE transaction on power Systems, vol17, No.4, Nov. 2002, pp. 943– 950Author’sProfile:Kusum Arora received M.TechDegree and AMIE Degree fromMDU, Rothak & Institution of Engrs.,Kolkata, in 2010 and 2002respectively. She is part of YMCAUniversity of Science & Technology. She ispursuing Ph.D in „Enhancing Power SystemQuality using FACTS Device‟.Dr.S.K.Agarwal received the M.TechDegree and PhD degree in ElectronicsEngg. from Delhi TechnicalUniversity, N. Delhi and Jamia MilliaIslamia Central University, N.Delhi in1998 and 2008 respectively. Since 1990, He hasbeen part of YMCA University of Science &Technology Faridabad (Haryana), as Dean andChairman in Department of ElectronicsEngineering. He has more than 40 publications injournals and national/international conferences ofrepute. His current research interests are in the fieldof Control System, electronics, biosensors, AnalogElectronics, wireless communication and digitalcircuits.Dr. Narendra Kumar received the M-Tech degree from AMU, Aligarh in1987 and PhD in Power Systems fromUniv. of Roorkee in 1996. He is part ofDelhi College of engineering, NewDelhi as Professor & HOD (Elect. Engg). He hasmore than 108 publications in journal,national/international conferences of repute. He hasunder taken an R&D project on „FACTS” and haswritten 3 books.DharamVir received M.Tech Degree& B.E. Degree in ECE from MDU,Rothak & Jamia Millia IslamiaCentral University, New Delhi in2008, 2004 respectively. He is part ofYMCA University of Science & Technology asHOS (EIC). He is pursuing PhD in „Power awarerouting in Mobile Ad hoc Networks‟.