Network Reconfiguration for Load Balancing in Distribution System with Distributed Generation and Capacitor Placement

Transcription

1 World Academy of Scence, Engneerng and Technology nternatonal Journal of Electrcal and Computer Engneerng Networ Reconfguraton for Load Balancng n Dstrbuton System wth Dstrbuted Generaton and Capactor Placement T. Lantharthong, N. Rugthacharoencheep nternatonal Scence ndex, Electrcal and Computer Engneerng waset.org/publcaton/11048 Abstract Ths paper presents an effcent algorthm for optmzaton of radal dstrbuton systems by a networ reconfguraton to balance feeder loads and elmnate overload condtons. The system load-balancng ndex s used to determne the loadng condtons of the system and maxmum system loadng capacty. The ndex value has to be mnmum n the optmal networ reconfguraton of load balancng. A method based on Tabu search algorthm, The Tabu search algorthm s employed to search for the optmal networ reconfguraton. The basc dea behnd the search s a move from a current soluton to ts neghborhood by effectvely utlzng a memory to provde an effcent search for optmalty. t presents low computatonal effort and s able to fnd good qualty confguratons. Smulaton results for a radal 69-bus system wth dstrbuted generatons and capactors placement. The study results show that the optmal on/off patterns of the swtches can be dentfed to gve the best networ reconfguraton nvolvng balancng of feeder loads whle respectng all the constrants. Keywords Networ reconfguraton, Dstrbuted generaton Capactor placement, Load balancng, Optmzaton technque T. NTRODUCTON HE electrc power dstrbuton systems consst of group of nterconnected radal crcuts and have a number of constrans le radal confguraton, all loads served, coordnated operaton of over current protectve devces, and voltage drop wthn lmts etc. Each feeder n the dstrbuton system has a dfferent mxture of commercal, resdental and ndustral type loads, wth daly load varatons. There are several operatonal schemes n electrcal dstrbuton systems; one of them s dstrbuton networ reconfguraton. There are some normally closed and normally opened swtches (sectonalzng and the swtches) n a dstrbuton feeder [1], []. Networ reconfguraton s very mportant for operatng the dstrbuton system. Generally, power dstrbuton networ reconfguraton provdes servces to as many customers as possble followng fault codng and durng planned outage for mantenance purposes wth system loss mnmzaton and load Balancng of the networ [3]. Thong Lantharthong s wth the Department of Electrcal Engneerng, Faculty of Engneerng, Rajamangala Unversty of Technology Phra Nahon, Bango, 10800, Thaland. (phone: ; fax: ; e-mal: thong.l@rmutp.ac.th). Nattachote Rugthacharoencheep s wth the Department of Electrcal Engneerng, Faculty of Engneerng, Rajamangala Unversty of Technology Phra Nahon, Bango, 10800, Thaland. (phone: ext. 150; fax: ext. 151; e-mal: nattachote@eee.org). Networ reconfguraton problem s a complex non-lnear combnatonal problem due to non-dfferental status of swtches and the normally open te swtches, determned to satsfy system requrement. From optmzaton pont of vew, the reconfguraton method have been used for loss reducton usng dfferent technques on the other hand from servce restoraton pont of vew, the reconfguraton allows to relocate loads by usng an approprate sequence of swtchng operatons wth operatng constrants taen nto account [4]. Networ reconfguraton of an electrcal dstrbuton system s an operaton to alter the topologcal structure of dstrbuton system by changng status (open/closed) of sectonalzng and te swtches. By transferrng loads from the heavly loaded feeders to the relatvely lghtly loaded feeders, the networ reconfguraton can balance feeder loads and elmnate overload condtons [5]. The system load-balancng ndex (LB) s used to determne the loadng condtons of the system and maxmum system loadng capacty. The ndex value has to be mnmum n the optmal networ reconfguraton of load balancng. For load balancng, the loads are requred to be rescheduled more effcently by modfyng the radal structure of the dstrbuton feeders. There are many exstng methods for determnng feeder confguraton. A Neural Networ based method wth mappng capablty to dentfy varous networ confguratons correspondng to dfferent load levels was proposed n [6]. An experts system usng heurstc rules to shrn the search space for reducng the computaton tme was presented n [7]. Kashem et al. [8] proposed an algorthm called dstance measurement technque (DMT) that found a loop frst and then a swtchng operaton was determned n that loop to mprove load balancng. Ao et al. [9] formulated the load balancng and servce restoraton problems by consderng the capacty and voltage constrants as a mxed nteger nonlnear optmzaton problem and converted the problem nto a seres of contnuous quadratc programmng sub problems. Baran and Wu [10] formulated the problem of loss mnmzaton and load balancng as an nteger programmng problem. H. D. Chang et al. [11] proposed a constraned mult objectve and non dfferentable optmzaton problem wth equalty and nequalty constrants for both loss reducton and load balancng. G. Pepons et al. [1] developed an mproved swtch-exchange method for load balancng problem, usng swtch exchange operatons. Muwanga [13] proposed a new load-balancng ndex and appled t to the networ for load balancng. n [14] presented a new load balancng and unbalanced algorthm n dstrbuton system for loss reducton. nternatonal Scholarly and Scentfc Research & nnovaton 6(4)

2 World Academy of Scence, Engneerng and Technology nternatonal Journal of Electrcal and Computer Engneerng nternatonal Scence ndex, Electrcal and Computer Engneerng waset.org/publcaton/11048 ncreasng trend of load growth n dstrbuton systems and the necessty for constructng new power plants as ts consequence, tendency toward applyng clean energes and ndependence from fossl fuels, have caused dstrbuted generaton (DG) to draw attenton to a great extent. Dstrbuted generaton (DG) s small-scale power generaton that s usually connected to or embedded n the dstrbuton system. The benefts of DG are numerous and the reasons for mplementng DGs are an energy effcency or ratonal use of energy, deregulaton or competton polcy, dversfcaton of energy sources, avalablty of modular generatng plant, ease of fndng stes for smaller generators, shorter constructon tmes and lower captal costs of smaller plants and proxmty of the generaton plant to heavy loads, whch reduces transmsson costs [15]. Among advantages of DGs one can menton mprovement n power qualty and relablty and reducton of loss, meanwhle usng DGs leads to complexty n operaton, control and protecton of dstrbuton systems [16]. njecton of DGs currents to a dstrbuton networ results n losng radal confguraton and consequently losng the exstng coordnaton among protecton devces. The applcaton of shunt capactors n dstrbuton systems has always been an mportant subject to dstrbuton engneers. The general capactor placement problem conssts of determnng the number, locaton, type, sze and control settngs at dfferent load levels of the capactors to be nstalled. Capactors are wdely nstalled n dstrbuton systems for reactve power compensaton to mprove the effcency of power dstrbuton va power and energy loss reducton, to mprove servce qualty va voltage regulaton and to acheve deferral of constructon, f possble, va system capacty release [17]. Capactor placement n dstrbuton feeder s the well nown effcent method for mprovng overall power delvery n an electrc dstrbuton system. The power loss n dstrbuton system s determned as functon of square of branch current whch conssts of real and reactve component. Ths paper emphaszes the advantage of networ reconfguraton to the dstrbuton system n the presence of DG unts and capactors placement for load balancng and bus voltage mprovement. The applcaton of Tabu Search s appled to determne the optmal on/off patterns of the swtches to mnmze the load balancng ndex subject to system constrants. The effectveness of the methodology s demonstrated by a practcal dstrbuton system consstng of 69 buses.. POWER FLOW EQUATONS Power flow n a radal dstrbuton networ can be descrbed by a set of recursve equatons called dst flow branch equatons that use the real power, reactve power and voltage at the sendng end of a branch to express the same quanttes at the recevng end of the branch [3]. Consderng the sngle-lne dagram depcted n Fg. 1 Fg. 1 Sngle-dagram of man feeder ( P Q ) P 1 P P L1 R, j1 ( P Q ) Q 1 Q 1 X, j1 1 ( R, 1 P X, 1 Q ) ( P ) (,,1 1 ) Q R X The power loss of the lne secton connectng between buses and +l may be computed as where ( P ) (, 1) Q P Loss R, 1 P, Q = actve and reactve power at bus = voltage of bus R, 1 = resstance of lne secton between buses and +1 X = reactance of lne secton between buses, 1 and +1. TABU SEARCH A. Bacground Tabu search s a meta-heurstc that gudes a local heurstc search strategy to explore the soluton space beyond local optmalty. Tabu search was developed by Glover and has been used to solve a wde range of hard optmzaton problems, such as resource plannng, telecommuncatons, fnancal analyss, schedulng, space plannng, and energy dstrbuton [18]. The basc dea behnd the search s a move from a current soluton to ts neghborhood by effectvely utlzng a memory to provde an effcent search for optmalty. The memory s called Tabu lst, whch stores attrbutes of solutons. n the search process, the solutons are n the Tabu lst cannot be a canddate of the next teraton. As a result, t helps nhbt choosng the same soluton many tmes and avod beng trapped nto cyclng of the solutons [19]. (1) () (3) (4) nternatonal Scholarly and Scentfc Research & nnovaton 6(4)

3 World Academy of Scence, Engneerng and Technology nternatonal Journal of Electrcal and Computer Engneerng nternatonal Scence ndex, Electrcal and Computer Engneerng waset.org/publcaton/11048 The qualty of a move n soluton space s assessed by aspraton crtera that provde a mechansm for overrdng the Tabu lst shown n Fgure. Aspraton crtera are analogous to a ftness functon of the genetc algorthm and the Bolzman functon n the smulated annealng. Fg. Mechansm of Tabu lst B. Neghborhood n the search process, a move to the best soluton n the neghborhood, although ts qualty s worse than the current soluton, s allowed. Ths strategy helps escape from local optmal and explore wder n the search space. A Tabu lst ncludes recently selected solutons that are forbdden to prevent cyclng. f the move s present n the Tabu lst, t s accepted only f t has a better aspraton level than the mnmal level so far. Fg. 3 [0] shows the man concept of a search drecton n Tabu search. Fg. 3 Search drecton of Tabu search. PROBLEM FORMULATON Loadng balance ndex (LB) represents the degree of loadng among feeders. The objectve of ths optmzaton problem can be expressed by the mnmzaton of the load balancng ndex (LB) as n equaton (5) [1]: \ æ ö t, Mn LB = å L (5) ÎB ç max çè ø where B = set of net wor branches formng loops L = length of branch t, = current capablty of branch for feeder reconfguraton pattern t max = maxmum current capablty of branch The objectve functon n (5) s subject to the followng constrants. 1) Power flow equatons. ) The voltage magntude at each bus must be mantaned wthn ts lmts expressed as follows: (6) mn max 3) Feeder capablty lmts:,max : {1,, 3,... l} (7) 4) Radal confguraton format. 5) No load-pont nterrupton. where = voltage at bus mn, max = mnmum and maxmum voltage = current flow n branch,max = maxmum current capablty of branch A flowchart for solvng the problem s shown n Fgure 4. Fg. 4 Flowchart of networ reconfguraton for load balancng. CASE STUDY The test system for the case study s a 1.66 radal dstrbuton system wth 69 buses, 7 laterals and 5 te-lnes (loopng branches), wth dstrbuted generaton and capactor placements as shown n Fgure 5. The current carryng capacty of branch No.1-9 s 400 A, No and No nternatonal Scholarly and Scentfc Research & nnovaton 6(4)

4 World Academy of Scence, Engneerng and Technology nternatonal Journal of Electrcal and Computer Engneerng nternatonal Scence ndex, Electrcal and Computer Engneerng waset.org/publcaton/11048 are 300 A and the other remanng branches ncludng the te lnes are 00 A. Each branch n the system has a sectonalzng swtch for reconfguraton purpose. The load data are gven n appendx Table A and branch data n Table A [1]. DGs are 4 small power producers who can provde only frm actve power to the system by ther DG unts. The producers are located at buses 14, 35, 36, and 53 wth capactes of 300, 00, 100, and 400 W, respectvely. Capactor located at buses 4, 45, 49, and 61 wth capactes of 100, 00, 300, and 400 Ar, respectvely. C Substaton W C W W 300 W Te swtches Sectonalzng swtches Load C4 63 Capactor Dstrbuted generaton C C1= 100 AR 6 C= 00 AR 6 C3= 300 AR 7 C4= 400 AR Fg. 5 Test system of 69-bus radal dstrbuton wth dstrbuted generaton and capactor placements The ntal statuses of all the sectonalzng swtches (swtches No. 1-68) are closed whle all the te-swtches (swtch No ) open. The total loads for ths test system are 3, W and, Ar. The feeder confguraton algorthm, based on Tabu search s used to search the most appropraton topology of the system. The mnmum and maxmum voltages are set at 0.95 and 1.05 p.u. The maxmum teraton for the Tabu search algorthm s 100. The fve cases are examned for networ reconfguraton for load balancng n dstrbuton system wth dstrbuted generaton and capactor placement n Table. TABLE CASE STUDY FOR LOAD BALANCNG N DSTRBUTON SYSTEM Case Networ Reconfguraton DGs Placement Capactor Placement The test results for the fve cases are summarzed n Table and Table. n case 1, the system power loss and the LB are hghest, and the mnmum bus voltage n the system volates the lower lmt of 0.95 per unt. t s confrmed from case 3 that the dstrbuted generaton help reduce the system loss from 4.68 W to W The mnmum load balancng ndex (LB) s 1.44 and power loss s W seen n case 5, where there are changes n branch currents after the reconfguraton. n cases and 5, all bus voltages satsfy the 0.95 p.u-voltage constrant. TABLE RESULTS FOR CASE STUDY 1, AND 3 Case 1 Case Case 3 Sectonalzng swtches to be open - 13, 0, 58, 63 14, 0, 5, 61 Te swtches to be closed - 70, 71, 7, 73 70, 71, 7, 73 Load balancng ndex (LB) Mnmum voltage (p.u.) Total power loss (W) TABLE RESULTS FOR CASE STUDY 4 AND 5 Case 4 Case 5 Sectonalzng swtches to be open 14, 0, 5, 61 14, 0, 53, 6 Te swtches to be closed 70, 71, 7, 73 70, 71, 7, 73 Load balancng ndex (LB) Mnmum voltage (p.u.) Total power loss (W) CONCLUSON n ths paper, an effcent jont strategy for networ reconfguraton n dstrbuton systems wth dstrbuted generaton and capactor placements. The applcaton of Tabu Search s appled to determne the optmal on/off patterns of the swtches to mnmze the load balancng ndex subject to system constrants. Load balancng are mportant complement to networ and feeder reconfguraton. Test results ndcate that the method can dentfy the most effectve networ reconfguraton for mprovement n load balancng. t s found that the optmal or near optmal confguraton for load balancng also loss reducton and mproves the voltage profle of the networ whle satsfyng all the constrants. Smulatons for a test system as well as a realstc system demonstrated the potental of use of the proposed technque that can be an useful tool for dstrbuton systems plannng and operaton. APPENDX LOAD DATA OF 69-BUS DSTRBUTON SYSTEM (W) (Ar) (W) (Ar) nternatonal Scholarly and Scentfc Research & nnovaton 6(4) 01 41

5 World Academy of Scence, Engneerng and Technology nternatonal Journal of Electrcal and Computer Engneerng nternatonal Scence ndex, Electrcal and Computer Engneerng waset.org/publcaton/11048 APPENDX (Contnued) (W) (Ar) (W) (Ar) APPENDX BRANCH DATA OF 69-BUS DSTRBUTON SYSTEM Branch Sendng Recevng R X APPENDX (Contnued) Branch Sendng Recevng R X Te lne ACKNOWLEDGMENT The authors would le to express hs grattude to Rajamangala Unversty of Technology Phra Nahon, Thaland for support. REFERENCES [1] D. Das, A fuzzy multobjectve approach for networ reconfguraton of dstrbuton systems, EEE Trans. Power Delvery, vol. 1, no 1, pp , Jan [] P. Ravbabu, K. enatesh, and C. S. Kumar, mplementaton of genetc algorthm for optmal networ reconfguraton n dstrbuton systems for load balancng, n Proc Conf. Computaton Technology n Electrcal and Electroncs Engneerng, Novosbrs, 008, pp [3] C. T. Su, and C. S. Lee, Networ reconfguraton of dstrbuton systems usng mproved mxed-nteger hybrd dfferental evoluton, EEE Trans. Power Delvery, vol. 18, no. 3, pp , July 003. [4] Y. K. Wu, and et al., Study of Reconfguraton for the dstrbuton system wth dstrbuted generators, EEE Trans. Power Delvery, vol. 5, no. 3, pp , July 010. [5] E. Carpaneto, G. Chcco, and J. S. Almal, Branch current decomposton method for loss allocaton n radal dstrbuton systems wth dstrbuted generaton, EEE Trans. Power Systems, vol. 1, no. 3, pp , Aug [6] H. Km, Y. o, and K. H. Jung, Artfcal neural networ based feeder reconfguraton for loss reducton n dstrbuton systems, EEE Trans Power Delvery, vol. 8, no. 3, pp , July [7] T. Taylor, and D. Lubeman, mplementaton of heurstc search strateges for dstrbuton feeder reconfguraton, EEE Trans Power Delvery, vol. 5, no. 1, pp.39-46, Jan [8] M. A. Kashem,. Ganapathy, and G. B. Jasmon, Networ reconfguraton for load balancng n dstrbuton networs, EE Proc.- Gener. Transm. Dstrb., vol. 146, no. 6, pp , Nov [9] K. Ao, and et al., An effcent algorthm for load balancng of transformers and feeders, EEE Trans. Power Delvery, vol. 3, no. 4, pp , Oct [10] M. E. Baran, and F. F. Wu, Networ reconfguraton n dstrbuton systems for loss reducton and load balancng, EEE Trans. Power Delvery, vol. 4, no., pp , Apr [11] H. D. Chang, and R.J Jumeau, Optmal networ reconfguratons n dstrbuton systems: Part 1: A new formulaton and a soluton nternatonal Scholarly and Scentfc Research & nnovaton 6(4)

6 World Academy of Scence, Engneerng and Technology nternatonal Journal of Electrcal and Computer Engneerng nternatonal Scence ndex, Electrcal and Computer Engneerng waset.org/publcaton/11048 methodology, EEE Trans. Power Delvery, vol. 5, no. 4, pp , Nov [1] G. Pepons, and M. Papadopoulos, Reconfguraton of radal dstrbuton networs: applcaton of heurstc methods on largescale networs, EE Proc., Gener., Transm. Dstrb, vol. 14, no. 6, pp , Nov [13] Muwanga and et al., Reconfguraton and load balancng n the L and M dstrbuton networs for optmal performance, EEE Trans. on Power Delvery, vol., no. 4, pp , Oct [14] G. K.. Raju, and P.R. Bjwe, Effcent reconfguraton of balanced and unbalanced dstrbuton systems for loss mnmzaton, EE Proc.- Gener. Transm. Dstrb., vol., no. 1, pp. 7-1, Jan [15] H. A. Gl, and G. Joos, Models for quantfyng the economc benefts of dstrbuted generaton, EEE Trans. Power Systems, vol. 3, no, pp , May 008. [16] G. Levtn, and et al., Optmal capactor allocaton n dstrbuton systems usng a genetc algorthm and a fast energy loss computaton technque, EEE Trans. on Power Delvery, vol. 15, no, pp , Oct [17]. H. M. Quezada, J. R. Abbad, and T. G. S. Roman, Assessment of energy dstrbuton losses for ncreasng penetraton of dstrbuted generaton, EEE Trans. Power Systems, vol. 1, no., pp , May 006. [18] B. Dengz, and C. Alabas, Smulaton optmzaton usng tabu search, n Conf. Wnter Smulaton, 000, pp [19] F. Glover, Tabu search-part, ORSA J. Computng, vol. 1, no.3, [0] H. Mor, and Y. Ogta, Parallel tabu search for capactor placement n radal dstrbuton system, n Conf. Power Engneerng Socety Wnter Meetng, 00, pp [1] J. S. Saver, and D. Das, mpact of networ reconfguraton on loss allocaton of radal dstrbuton systems, EEE Trans. Power Delvery, vol., no. 4, pp , Oct Thong Lantharthong receved hs M.Eng n Electrcal Engneerng from Rajamangala Unversty of Technology Thanyabur, Thaland n 010. He s currently a lecturer at the Department of Electrcal Engneerng, Faculty of Engneerng, Rajamangala Unversty of Technology Phra Nahon (RMUTP), Bango, Thaland. Hs research nterests nclude, power system plannng, optmzaton technque, and renewable energy. Nattachote Rugthacharoencheep (M 10) receved hs Ph.D. n Electrcal Engneerng from Kng Mongut s Unversty of Technology North Bango (KMUTNB), Thaland n 010. He s currently a lecturer at the Department of Electrcal Engneerng, Faculty of Engneerng Rajamangala Unversty of Technology Phra Nahon (RMUTP), Bango, Thaland. Hs research nterests nclude power system operaton, optmzaton technque, and dstrbuted generaton. nternatonal Scholarly and Scentfc Research & nnovaton 6(4)