International Journal of Computational Engineering Research(IJCER)


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International Journal of Computational Engineering Research(IJCER)

  1. 1. I nternational Journal Of Computational Engineering Research ( Vol. 2 Issue. 6 Optimal Location of TCSC by Sensitivity Methods 1 Madhura Gad, 2Prachi Shinde , 3Prof. S.U.Kulkarni 1, 2, 3 Depart ment of Electrical Eng ineering, Bharati Vidyapeeth Deemed University College of Eng ineering , PuneAbstract - Due to the deregulation of the electrical market,  Transmission & Distribution; supply the electric demanddifficulty in acquiring rights -of-way to build new without exceeding the thermal limit.transmission lines, and steady increase in power demand,  In large power system, stability problems causing powermaintaining power system stability beco mes a difficult and disruptions and blackouts leading to huge losses.very challenging problem. In a competit ive power market, These constraints affect the quality of powerthe system is said to be congested when the volume of delivered. However, these constraints can be suppressed bytransactions exceeds the transfer capability of the enhancing the power system control. Congestion may betransmission corridor. allev iated through various ways. Among the technical In deregulated electricity market transmission solutions, we have system red ispatch, system reconfiguration,congestion occurs when there is insufficient transmission outaging of congested lines, operation of FACTS devices andcapacity to simu ltaneously accommodate all constraints for operation of transformer tap changers [10][17].transmission of a line. FACTS devices can be an alternative The issue of transmission congestion is moreto reduce the flows in heavily loaded lines, resulting in an pronounced in deregulated and competitive markets and itincreased loadability, low system loss, improved stability of needs a special treatment. In this environment, independentthe network, reduced cost of production and fulfilled system operator (ISO) has to relieve the congestion, so thatcontractual requirement by controlling the power flow in the the system is maintained in secure state. To relieve thenetwork. congestion ISO can use follo wings techniques [16], A method to determine the optimal location of  Out-ageing of congested linesTCSC has been suggested in this paper. The approach is  Operation of transformer taps/phase shifters [9]based on the sensitivity of the reduction of total system  Operation of FACTS devices particularly series devicesreactive power loss and real power performance index.  Re-d ispatching the generation amounts. By using this The proposed method has been demonstrated on 5- method, some generators back down wh ile others increasebus power systems. their output. The effect of re-dispatching is that generators no longer operate at equal incremental costs.Keywords: Congestion, Co mpensation, Deregulated Power  Curtailment of loads and the exercise of load interruptionSystem, Flexible A C Transmission Systems (FACTS), options [13]Optimal location, Performance Index, Thyristor Controlled FACTS devices are utilized as one of suchSeries Capacitor (TCSC), Stat ic Modelling. technology which can reduce the transmission congestion and leads to better using of the existing grid infrastructure. I. Introduction Besides, using FACTS devices gives more opportunity to The increasing industrialization, urbanizat ion of life ISO [16].style has lead to increasing dependency on the electrical Thyristor Controlled Series Capacitor (TCSC) is aenergy. This has resulted into rapid growth of power systems. variable impedance type FACTS device and is connected inThis rapid growth has resulted into few uncertainties. Power series with the transmission line to increase the powerdisruptions and individual power outages are one of the transfer capability, imp rove transient stability, and reducemajor problems and affect the economy of any country. In transmission losses[6].contrast to the rapid changes in technologies and the power This paper deals with the location aspect of therequired by these technologies, transmission systems are series FACTS devices, especially to manage congestion inbeing pushed to operate closer to their stability limits and at the deregulated electricity markets. The location of FA CTSthe same time reaching their thermal limits due to the fact devices can be based on static or dynamic performance of thethat the delivery of power have been increasing. If the system. Sensitiv ity factor methods are used to determine theexchanges were not controlled, some lines located on suitable location for FA CTS devices [1][2][3].particular paths may become overloaded, this phenomenon is This paper presents the comparative analysis ofcalled congestion. The major problems faced by power methodologies based on real power Performance Index andindustries in establishing the match between supply and reduction of total system VA R power losses for properdemand are: location for congestion management in the deregulat ed electricity markets. Issn 2250-3005(online) October | 2012 Page 162
  2. 2. I nternational Journal Of Computational Engineering Research ( Vol. 2 Issue. 6 capacitor is inserted directly in series with the transmission II. Flexible Ac Transmission System (Facts) line and the thyristor-controlled inductor is mounted directly The FACTS is a generic term representing the in parallel with the capacitor. Thus no interfacing equipmentapplication of power electronics based solutions to AC power like for example h igh voltage transformers is required. Thesystem. These systems can provide compensation in series or bi-directional thyristor valve is fired with an angle α rangingshunt or a combination of both series and shunt. The FACTS between 90° and 180° with respect to the capacitor voltage.can attempt the compensation by modifying impedance, This makes TCSC much more econo mic than somevoltage or phase angle. FA CTS devices can be connected to a other competing FACTS technologies. Thus it makes TCSCtransmission line in various ways, such as in series with the simp le and easy to understand the operation. Seriespower system (series compensation), in shunt with the power compensation will;system (shunt compensation), or both in series and shunt.  Increase power transmission capability.  Improve system stability.2.1 SERIES FA CTS : The series Co mpensator could be  Reduce system losses.variable impedance, such as capacitor, reactor, etc. or a  Improve voltage profile of the lines.power electronics based variable source of main frequency to  Optimize power flow between parallel lines.serve the desired need. Various Series connected FACTSdevices are[17]; Static Synchronous Series Co mpensator (SSSC) Thyristor Controlled Series Capacitor (TCSC) Thyristor Switched Series Capacitor (TSSC) Thyristor Controlled Series Reactor (TCSR) Thyristor Switched Series Reactor (TSSR)2.2 SHUNT FA CTS : Shunt Controllers may be variable Fig 1 : Schemat ic diagram of TCSCimpedance, variab le source, or a co mb ination of these. Inprinciple, all shunt Controllers inject current into the systemat the point of connection. Various shunt connectedcontrollers are; Static Synchronous Series Co mpensator (STATCOM ) Static VA R Co mpensator (SVC) Thyristor Controlled Reactor (TCR) Thyristor Switched Capacitor (TCS)2.3 COMBINED SHUNT – Series Controller: This may be acombination of separate shunt and series controllers, wh ichare controlled in a coordinated manner or a Unified PowerFlow Controller with series and shunt elements. In principle, Fig 2 : Variation of impedance in case of TCSCcombined shunt and series controllers inject current into thesystem with shunt part of controller and voltage with th e Fig.2 shows the impedance characteristics curve of aseries part of controller. Various combined series shunt TCSC device [2][17]. It is drawn between effective reactanceControllers are: Various combined series shunt Controllers of TCSC and firing angle α. The effective reactance of TCSCare; starts increasing from XL value to till occurrence of parallel resonance condition XL(α)=XC, theoretically XTCSC is infin ity. Unified Power Flow Controller This region is inductive region. Further increasing of XL(α) Thyristor Controlled Phase Shifter gives capacitive region, Starts decreasing fro m infinity point to min imu m value of capacitive reactance XC. Thus, III. Chracteristics & Static Modeling Of TCSC impedance characteristics of TCSC shows, both capacitive3.1 CHA RA CTERISITCS: Thyristor Controlled Series and inductive region are possible though varying firing angleCapacitor (TCSC) is a series compensator which increases (α).transmission line capacity by decreasing lines’ series  90 < α < Llim Inductive regionimpedances and increase network reliability. The TCSC  Clim < α <180 Capacit ive regionconcept is that it uses an extremely simp le main circuit. TheIssn 2250-3005(online) October | 2012 Page 163
  3. 3. I nternational Journal Of Computational Engineering Research ( Vol. 2 Issue. 6 Llim < α < Clim Resonance region While selecting inductance, XL should besufficiently s maller than that of the capacitor Xc . Since toget both effective inductive and capacitive reactance acrossthe device. Suppose if Xc is smaller than the XL , then onlycapacitive region is possible in impedance characteristics. Inany shunt network, the effective value of reactance followsthe lesser reactance present in the branch. So only onecapacitive reactance region will appears. Also XL should notbe equal to Xc value; or else a resonance develops that result Fig 3 : Model of Trans mission linein infinite impedance an unacceptable condition andtransmission line would be an open circuit. The model of transmission line with a TCSC The impedance of TCSC circuit is that for a parallel connected between bus-i and bus-j is shown in Fig.4. DuringLC circu it and is given by; the steady state the TCSC can be considered as a static reactance -jXc . The real and reactive power flo w fro m bus -i (1) to bus-j, and fro m bus-j to bus-i of a line having series impedance and a series reactance are,Where (7) (2) is the firing angle , (8) is the reactance of the inductor and Xl() is the effective (9)reactance of the inductor at firing angle  and is limited thus: (10)3.2 STATIC M ODLING : The Fig 3 shows a simpletransmission line represented by its lumped pi equivalentparameters connected between bus -i and bus-j. Let comp lexvoltage at bus-i and bus-j are Vi < i and Vj < j respectively. The real and reactive power flow fro m bus-i tobus-j can be written as [1], (3) (4) Fig 4 : Model of Transmission line with TCSCWhere ij = i-j , similarly the real and reactive power flow The active and reactive power loss in the line havingfro m bus-j to bus-i is; TCSC can be written as, (11) (5) (6) (12) Where, (13) The change in the line flo w due to series capacitance can be represented as a line without series capacitance withIssn 2250-3005(online) October | 2012 Page 164
  4. 4. I nternational Journal Of Computational Engineering Research ( Vol. 2 Issue. 6power injected at the receiving and sending ends of the line Where PLm is the real power flow and max isas shown in Fig.5. the rated capacity of line-m, n is the exponent, NL is number of lines and Wm a real non-negative weighting coefficient which may be used to reflect the importance of lines. PI will be small when all the lines are within their limits and reach a high value when there are overloads. Thus, it provides a good measure of severity of the line overloads for given state of Fig 5 : Inject ion Model of TCSC the power system. Most of the works on contingency selection algorith ms utilize the second order performance The real and reactive power injections at bus -i and indices which, in general, suffer fro m masking effects. Thebus-j can be expressed as, lack of discrimination, in which the performance index for a (14) case with many small vio lations may be comparable in value to the index for a case with one huge violation, is known as (15) masking effect. By most of the operational standards, the system with one huge violation is much more severe than that (16) with many small violat ions. Masking effect to some extent can be avoided using higher order performance indices, that (17) is n > 1. However, in this study, the value of exponent hasWhere, been taken as 2 and Wi =1. The real power flow PI sensitivity factors with (18) respect to the parameters of TCSC can be defined as, (22) (19) Where Xck is the value of the reactance, as provided by theThis Model of TCSC is used to properly modify the TCSC installed on line k.parameters of transmission line with TCSC for optimal The sensitivity of PI with respect to TCSClocation. parameter connected between bus -i and bus-j can be written as; IV. Optimal Location of TCSC4.1 REDUCTION OF TOTA L SYSTEM REA CTIVE (23)POW ER LOSS: [1][2][3] A method based on the sensitivityof the total system reactive power loss with respect to thecontrol variable of the TCSC. For TCSC p laced between The real power flow in a line-m can be representedbuses i and j we consider net line series reactance as a control in terms of real power in jections using DC power flowparameter. Loss sensitivity with respect to control parameter equations where s is slack bus, as,of TCSC p laced between buses i and j can be written as, (24) (20)4.2 REA L POW ER FLOW PERFORMANCE INDEXSENSITIVITY INDICES: The severity of the system loading Using equation-24, the following relationship can be derived,under normal and contingency cases can be described by areal power line flo w performance index, as given below [4], (25) (21)Issn 2250-3005(online) October | 2012 Page 165
  5. 5. I nternational Journal Of Computational Engineering Research ( Vol. 2 Issue. 6The term, (26) Table-1 : Power flow of 5-Bus System & its limit Line From- Real Real Powercan be derived as, To Power flow Li mit 1 1 2 flow (pu) 0.93 (pu) 1 (27) 2 1 3 0.525 0.8 3 2 3 -0.019 0.7 4 2 4 0.081 0.8 5 2 5 0.452 0.6 6 3 4 0.586 0.6 7 4 5 0.162 0.6 Table-2 : Calculated Sensitivity Indices (28) Line aij bi j 1 0.0326 2.0957 2 0.1048 0.3189 3 0.0036 0.00104.3 CRITERIA FOR OPTIMAL LOCATION: 4 0.0041 0.0141 The TCSC device should be placed on the most 5 0.0009 1.4953sensitive line. With the sensitivity indices computed for 6 0.0006 5.7528TCSC, following criteria can be used for its optimal 7 0.0011 -0.0195placement [1][2][3]. In reactive power loss reduction method TCSC should be The sensitive of reactive power loss reduction and placed in a line having the most positive loss sensitivity real power flow performance index with respect to TCSC index. control parameter has been computed and are shown in table In PI method TCSC should be placed in a line having 2. The sensitive lines are highlighted in table-2. It can be most negative sensitivity index. observed from table -2 that line 2 is more sensitive as per Reduction of total system reactive power loss method. Line 7 V. S IMULATION & RES ULTS is more sensitive as per real power flow performance index In order to find the optimal locations of TCSC, we have to method but line 3 & 4 can also be considered because theseimplement analysis over 5-bus system as shown in below fig. line also seems to be sensitive. System power flow result MATLAB software has been used for simulation. after placing TCSC in 2,3,4 & 7 is shown in table-4. The value of control parameter o f TCSC for co mputing power flow are taken as per table-3. 1 3 4 Table-3 : Control Parameter (Xtcsc) Line Compensati on TCSC 2 K’ 0.70 parameter in 0.0588 pu , XTCSC 2 7 0.70 0.168 5 3 0.70 0.126 Fig 6 : 5-Bus System 4 0.70 0.126 Power flow of above 5-bus system & line limit isshown in table-1. Fro m the load flow, it was found that realpower flow in line-1 is 0.93pu & line-6 is 0.586, which isvery near to its line loading limit & may create congestion.Issn 2250-3005(online) October | 2012 Page 166
  6. 6. I nternational Journal Of Computational Engineering Research ( Vol. 2 Issue. 6 Where, PL is power flow in line K (M VA ) & c is unit investment cost of TCSC. Here it is considered 22000 Table-4 : Power Flow after placing TCSC $/M VA-year[5]. Xc is TCSC reactance in pu. Power Power Power Power Power flow flow flow The objective function for placement of TCSC will be[3], flow flow withLine with with with without TCS C in TCS C TCS C TCS C in TCS C line 4 The bid prices of generators for 5 bus system are in line 2 in line 7 line 3 given in table-6, where P is in MW and $ is a mo mentary unit 1 0.93 0.861 0.918 0.954 0.980 which may be scaled by any arbitrary constant without 2 0.525 0.722 0.539 0.500 0.473 affecting the results and Pimin , Pimax are generation power limits of each generator. 3 -0.019 -0.032 0.023 0.005 -0.046 4 0.081 0.056 0.130 0.081 0.177 Table-6 : Bid Prices of Generators [1] 5 0.452 0.441 0.350 0.451 0.431 6 0.586 0.516 0.640 0.586 0.511 7 0.162 0.174 0.264 0.163 0.183 Table-5 : Reactive power Loss Total cost of two methods is shown below chart. ItLine Re active Re active Reactive Reactive Reactive can be observed that placement of TCSC in line -7 is more power power power power power economical than the placement of TCSC in line-2 for loss w/o loss with loss with loss with loss with TCSC TCSC in TCSC in TCSC in TCSC in congestion management. Fro m this we can say that PI line 2 line 7 line 3 line 4 method is more economical than reduction of total system 1 0.047 0.041 0.046 0.050 0.052 reactive power loss method for installing the TCSC and congestion relief. 2 0.021 0.012 0.023 0.019 0.017 3 0.002 0.004 0.000 0.000 0.001 4 0.004 0.004 0.004 0.002 0.002 5 0.035 0.035 0.023 0.034 0.032 6 0.011 0.008 0.014 0.012 0.009 7 0.007 0.008 0.006 0.008 0.010Tota 0.127 0.112 0.116 0.125 0.122 l It can be observed from table-4 that congestion hasbeen relieved in line 1 & 6 after p lacing TCSC in line 2 andalso reduced system reactive power loss. There is not much imp rovement in congestion & PIafter placing TCSC in 3 & 4 but as seen in table-2 that line 7is more sensitive & hence placing TCSC in line 7 is optimal Fig 7 : Cost comparisonfor reducing PI & congestion relief. VI. Conclusion 5.1 Total Costs of Two Methods: Congestion management is an important issue in Due to high cost of FACTS devices, it is necessary deregulated power systems. FACTS devices such as TCSCto use cost benefit analysis to analyze whether new FACTS by controlling the power flows in the network can help todevice is cost effective among several candidate locations reduce the flows in heavily loaded lines. Because of thewhere they actually installed. The TCSC cost in line-k is considerable costs of FACTS devices, it is important togiven by [2][3], obtain optimal location for placement of these devices. Here two sensitivity-based methods have been developed for determin ing the optimal location of TCSC in an electricity market. In a system, first two optimal locationsIssn 2250-3005(online) October | 2012 Page 167
  7. 7. I nternational Journal Of Computational Engineering Research ( Vol. 2 Issue. 6of TCSC can be achieved based on the sensitivity factors aij [10] A.R. Abhyankar, Prof.S.A.Khaparde, “Introduction toand bij and then optimal location is selected based on Deregulation in Power Industry” IIT M umbai.minimizing production cost plus device cost. Test results [11] Text Book by Hadi Saadat, “Power System Analysis”Dr . Ibrahim Oumarou, Prof. Daozhuo Jiang, Prof. Cao Yijiaobtained for 5-bus power systems show that sensitivity “Optimal Placement of Shunt Connected Facts Device in afactors could be effectively used for determining optimal Series Compensated Long Transmission Line” Proceedingslocation of TCSC. The cost values for two sensitivity of the World Congress on Engineering 2009 Vol I, WCEmethods were compared. Test results divulge that the 2009, July 1 - 3, 2009, London, U.K.proposed methodology is effective in managing congestion & [12] Elango.K., S.R.Paranjothi, C.Sharmeela “Transmissionoptimal location of TCSC. Congestion M anagement in Restructured Power Systems by Generation Rescheduling and Load Shedding using RuleSCOPE & FUT URE WORK: Based OPF” The complet ion of project opens the avenues for European Journal of Scientific Research, ISSN 1450-216X Vol.57 No.3 (2011), pp.380-390, © EuroJournals Publishing,work in many other related areas. The one of the area is Inc. 2011, of TCSC on line outage in order to relieve congestion [13] S.N. Singh and A. K. David, “Optimal location of FACTScan be studied. devices for congestion management,” Electric Power Systems Research, vol. 58, pp. 71-79, Oct. 2000. References [14] E.V. Larsen, K.Clark, S.A.M iske.Jr, J.Urbanek,“[1] Seyed Abbas Taher, Hadi Besharat, “Transmission Congestion Characteristics and rating consideration of Thyristor M anagement by Determining Optimal Location of FACTS controlled series compensation”, IEEE Transactions on Power Devices in Deregulated Power Systems” American Journal of Delivery, Vol. 9. No. 2, April 1994. Applied Sciences 5 (3): 242-247, 2008 , [15] D. Shirmohammadi, B. Wollenberg, A. Vojdani, P.[2] Anwar S. Siddiqui, Rashmi Jain, M ajid Jamil and Gupta C. P. Sandrin,M . Pereira,F. Rahimi, T. Schneider, and B. Stott, “Congestion management in high voltage transmission line “Transmission dispatch and congestion management in the using thyrister controlled series capacitors” Journal of emerging energy market structures,” IEEE Trans. Power Electrical and Electronics Engineering Research Vol. 3(8), Syst., vol. 13, pp. 1466-1474, Nov. 1998. pp.151-161,October2011,Available online at [16] Text Book by N.G Hingorani & Lazlo Ghyghi. “Understaning , ISSN – 2141 – 2367 FACT” Concept and technology of FACT” ©2011 Academic Journals[3] L.Rajalakshmi, M .V.Suganyadevi, S.Parameswari “Congestion M anagement in Deregulated Power System by Locating Series Madhura Gad : M.Tech Student in FACTS Devices” International Journal of Computer Electrical Power Systems, Applications (0975 – 8887) Volume 13– No.8, January 2011 Bharati Vidyapeeth Deemed Un iversity[4] M rinal Ranjan, B. Vedik, “Optimal Location of FACTS College of Engineering, Pune, Devices in a Power System by M eans of Sensitivity Analysis” Maharashtra, India Science Road Publishing Corporation, Trends in Electrical and Computer Engineering TECE 1(1) 1-9, 2011 Mrs. S.U.Kulkarni: Associate professor,[5] Nazanin Hosseinipoor, Syed M .H Nabavi, “Optimal Locating Depart ment of Electrical Eng ineering, and Sizing of TCSC Using Genetic Algorithm for Congestion Bharati Vidyapeeth Deemed Un iversity M anagement in Deregualted Power M arkets” ,Co llege of Engineering -Pune[6] D. M urali, Dr. M . Rajaram, N. Reka “Comparison of FACTS She has completed ME fro m Govern ment Devices for Power System Stability Enhancement” College of Engineering –Pune. Her areas of International Journal of Computer Applications (0975 – 8887) interest are power system protection, Volume 8– No.4, October 2010[7] Naresh Acharya, N. M ithulananthan “Locating series FACTS automation in power system. devices for congestion management in deregulated electricity markets” Electric Power Systems Research 77 (2007) 352–360 Prachi Shinde: M.Tech Student in[8] Zamani, F., V., Kazemi, A., M ajd, B., A., “Congestion Electrical Power Systems, M anagement in Bilateral Based Power matket by FACT Bharati Vidyapeeth Deemed University Devices and load curtailments ” College of Eng ineering Pune,[9] Hossein Nasir Aghdam “Analysis of Phase-Shifting Maharashtra, India Transformer (PST), on Congestion management and Voltage Profile in Power System by MATLAB/Simulink Toolbox”Issn 2250-3005(online) October | 2012 Page 168