Optimal Coordination of Overcurrent Relays Based on Modified Bat Optimization Algorithm

Transcription

1 Internatonal Electrcal Engneerng Journal (IEEJ) Optmal Coordnaton of Overcurrent Based on Modfed Bat Optmzaton Algorthm Reza Kherollah, Farhad Namdar Department of Power and Computer, Engneerng Faculty, Tarbat Modares Unversty, Tehran, Iran Engneerng Faculty, Lorestan Unversty, Lorestan, Iran Abstract the oblgaton of protectve systems s the tmely detecton of fault and removng t from the power network. Protecton of the power systems ncludes varous types of optmzatons that ther goal s to become economcally approprate, to ncrease the level of stablty and to secure the network. There are two crucal elements n determnng and choosng optmzng algorthms n protectve functons; the accuracy of the results and reducng the executon tme of the optmzng algorthm. Optmzng the coordnaton of drectonal Over Current plays an mportant role n the favorable functonng of the related protectve systems. In ths artcle, n addton to functonally elaboratng the Bat Optmzaton Algorthm (BOA) and the ssue of optmal coordnaton of drectonal overcurrent relays, n lne wth the reducton of the tme of executon optmzng algorthm; some new modfcatons has been appled to the algorthm whle mprovng the accuracy of output results. The suggested approach s appled to two standard power system networks. Results show the effectveness of the proposed modfed Bat Optmzaton Algorthm n comparson wth prevous studes on optmal coordnaton of overcurrent relays. Index Terms Bat Optmzaton Algorthm, Optmzaton methods, Overcurrent protecton, Power system protecton. M I. INTRODUCTION ODERN power systems are susceptble to extendng over a wde area of falures. Power demand s prolferated then the operaton, stablty, and plannng of large nterconnected power system are becomng more and more complex, so the power system wll be less secure system [].The electrcal energy transmsson lnes, as a sgnfcant part of a power network, have a crucal part n stablty and favorable operaton of systems. Ths part of the power network often falls under the nfluence of numerous faults and leads to the ncrease of the currents n upper levels. If these faults are not separated n tme, they cause the loss of stablty, damage the equpment of the system and blackout the network. So the role of protectng functons n protectve systems s to detect faults tmely and correctly and to remove them from other parts of the network. Drectonal overcurrent relays that have a smple functonal comprehenson and are fnancally proftable, are a sutable choce to use n protectve systems. These relays are used as prmary protectons n dstrbuton and sub-transmsson networks and also as backup protecton n transmsson lnes. The ssue of coordnaton of overcurrent relays ncludes tme settng multplers (TSM) and plug settng (PS) wth applyng related constrants on operatng tme dfference between backup and prmary relays. Over the past fve decades, several studes on optmal coordnaton of overcurrent relays has been carred out. These studes can be dvded nto three categores: ) Tral and error method ) Structural analyss method ) Optmzaton method []. In optmzaton method, nonlnear programmng s used n order to calculate the values of PS and TSM n relays []-[] whle n lnear programmng, the coeffcents of TSM are determned by consderng the values of PS n a default mode [5]. In recent years, artfcal ntellgence methods and nature-nspred algorthms such as Evoluton Programmng [6], Genetc Algorthm (GA) []-[9], Partcle Swarm Algorthm (PSO) [0]-[] among others are used to solve the ssue of optmal coordnaton of overcurrent relays. One other nature-nspred optmzaton algorthm s the Bat Optmzaton Algorthm (BOA), whch s based on the behavor of sound reflecton n mcrobats. Ths s a populaton-based algorthm that has been put forward by Yang [] to solve optmzaton problems. In recent years, there have been several studes about the BOA such as Mult-objectve Optmzaton Bat Algorthm [], Fuzzy logc Bat Algorthm [], K-means Bat Algorthm [6], Chaotc Bat Algorthm [], Bnary Bat Algorthm [] and Dfferental Operator and L evy Flght bat Algorthm [9]. Kherollah and Namdar Optmal Coordnaton of Overcurrent Based on Modfed Bat Optmzaton Algorthm

2 Internatonal Electrcal Engneerng Journal (IEEJ) Radha and Valarmath [0] have used BOA to detect and optmze phshng webstes by addng the Doppler Effect. Bora et al. [] have appled the BOA to solve the ssue of brushless DC wheel motor. Tsa et al. [] have used the BOA to the numercal optmzaton ssue. Sakthvel et al. [] have used the BOA to solve the economc load dspatch optmzaton ssue. II. THE ISSUE OF OPTIMIZATION Settngs related to drectonal overcurrent relays accordng to tme-current characterstcs conssts of the determnaton of TSM and the PS. In ths artcle, the PS quanttes between the mnmum and the maxmum values of load current are consdered by default accordng to the power flow of network n queston and also wth respect to the turn rato of current transformers, so that the results of appled optmzaton algorthm nclude the TSM rates. The PS n relays are apponted on 5-percent steps, n the form of steps between 50 to 00 percent. Mohamad et al. [] have proposed the followng objectve functon to optmze the operatng tme of relays by symmetrcal three-phase short-crcut faults near to crcut breakers of man relays and also to apply constrants related to the operatng tme dfference between backup and prmary relays: N P ( ) k () OF t t t n whch N s the number of relays, P represents the number of backup and prmary relay pars, k represents each of the backup and prmary relay pars, t shows the operatng tme of the th relay, and t s the operatng tme dfference between the prmary and backup relay pars and s defned as t = t b -t m -CTI n whch CTI s the defned coordnaton tme n relay characterstcs for prmary and backup relay pars. In ths paper, ths value has been consdered as 0., s a fxed multpler and s defned as = α * β and s determned by the tral and error method. The frst part of the Equaton () s related to the optmal operatng tme for relays and the second part ncludes the applcaton of the constrants related to the operatng tme dfference of prmary and backup relay pars. All the used overcurrent relays have the IEC nverse standard characterstc and the tme-current characterstc of ts current accordng to the standards s as the followng: t = TSM * ISC Ip n () In whch ISC and Ip are the values of short crcut currents and the PS n relays, respectvely. The values of TSM are defned n a contnuous manner and wth respect to the -percent steps n relay characterstcs. III. BAT OPTIMIZATION ALGORITHM The most promnent capablty seen n bats s the sound pulse emsson and hearng the echo resulted from the surface of the materals around whch they use to dstngush the surroundng envronment and to fnd food. These anmals use a knd of sound emsson and detecton devce that s called echolocaton. Most bats use echolocaton to a defnte degree, whle mcrobats use ths behavor to a great extent. These creatures produce a very loud sound pulse and lsten to ts resultng echo to analyze the upcomng stuaton. Each sound pulse ncludes frequency, loudness, and pulse emsson rate. Most bats use sgnals wth tunng frequences whle the rest use fxed-frequency sgnals. The frequency range used by these creatures s between 5 KHz to 0 KHz. Yang [] has approved some of ther characterstcs as deal n order to acheve an optmzaton algorthm based on the echolocaton behavor of bats:. All bats use echolocaton and dstngush the dfference between prey and obstacle.. Bats are flyng wth a random velocty ( v ), n a random locaton ( x ), wth a frequency n the range of [f mn, f max ], wth a loudness ( A ) and the pulse emsson rate ( r ). They can set the loudness A, pulse emsson rate r and the frequency f when approachng to food.. It s assumed that the ray tracng characterstc s not used for detectng the tme delay and the D topology. In behavor smulaton of bats echolocaton, updatng the velocty and the locaton of bats when approachng to food s descrbed as the followng: f f ( f f ) () mn max mn v v (x x ) f () x t t t * x v (5) t t t In whch s a random parameter between [0, ], and v are respectvely the locaton and the velocty of the th bat n a D space, * x s the best acheved stuaton for bats n every teraton. If one soluton among the best x Kherollah and Namdar Optmal Coordnaton of Overcurrent Based on Modfed Bat Optmzaton Algorthm

3 Internatonal Electrcal Engneerng Journal (IEEJ) exstng solutons s chosen n the local search part, then the new soluton for every bat s as the followng: t x x (A ) (6) new old In whch A t s the loudness average of bats n each generaton and s a random parameter n the range of [-, ]. Consderng the echolocaton behavor of bats when approachng food, the loudness of A and the pulse emsson rate r of the bat approachng food s calculated n the followng way: r r ( exp( t)) () 0 A A 0 () In whch and are the values of the fxed and controlled parameters n algorthm. If n the BOA, A = 0 0 and r 0 = are n the form of constants n the process of applyng the algorthm, and f s produced randomly n each teraton, the result s the Partcle Swarm Optmzaton algorthm. If the velocty s not used and the values of r and A are assumed as fxed, the process of optmzng the algorthm would be the Harmony search []. The advantage of BOA over Partcle Swarm Optmzaton and Genetc Algorthms has been proved []. The pseudo code related to the BOA was mentoned by Yang []. controllng parameters, whch are the loudness ( A ) and the pulse emsson rate ( r ) (Equatons and ), and also the ntensve local search (Equaton 6). Ths causes an algorthm convergence to the optmum pont of the ssue n less teraton, and reduces the executon tme of the optmzaton algorthm wth preservng the accuracy of the output results.. CASE STUDY V. SIMULATION RESULTS Fgure depcts an -busbars ( kv buses) test system that ncludes 9 transmsson lnes, transformers, and drectonal overcurrent relays. All the overcurrent relays have the IEC nverse standard characterstcs. The bus # s connected to a network wth the short-crcut capacty of 00 MVA. The parameters employed n the network are taken from Bedekar and Bhde [5]. Short-crcut currents passng through the prmary and backup relays per every symmetrcal three phase short-crcut fault occurrng near the crcut breaker of the prmary relay are ncluded n appendx A. IV. PROPOSAL METHOD The executon tme of the optmzaton algorthm s an mportant factor n choosng t n many protectve functons. The superorty of BOA n the accuracy of the output results over other optmzaton algorthms lke PSO and GA has been proved [], but the problem wth whch all the optmzaton algorthms face s ther need to run the algorthm several tmes to reach a desrable result n the output. If the executon tme of the BOA has been reduced to a sgnfcant extent n comparson to other algorthms and preserve the accuracy of the output results, ths algorthm can be the frst choce to be appled n optmzng problems n many cases n whch tme s a determnng parameter n the desred functonng of protectve systems. If the algorthm can reach to the optmum pont of ssue n fewer numbers of teratons, then the executon tme of the algorthm would reduce. To adjust the BOA, updatng the velocty of bats n for each teraton has been gnored and ths velocty would be constant through the whole process of executon the algorthm. By the velocty of bats beng constant n executon the algorthm, updatng the locaton of bats s carred out n each teraton wth respect to the Kherollah and Namdar Fg. -busbars test system. RESULTS AND DISCUSSION In order to have a desrable functonng demonstraton of the proposed modfed algorthm, the BOA [] has been appled to the optmal coordnaton of overcurrent relays problem. The controllng parameters of the BOA are ncluded n Table. In order to verfy the accuracy of the results, all the smulatons have been carred out on one computer. The numbers of α and β on the objectve Optmal Coordnaton of Overcurrent Based on Modfed Bat Optmzaton Algorthm 5

4 Internatonal Electrcal Engneerng Journal (IEEJ) Fg. Runnng both optmzaton algorthms (modfed BOA and BOA) n 0 tmes for network #. functon are consdered as and 00, respectvely. The BOA [] wth 000 tmes of teraton and n accordance wth the controllng parameters (Table ) s run n 0 tmes of the executon of algorthm and accordng to the results extracted from ts output (tme settng multplers), the average value of objectve functon equals to. and n 9.s tme. Now the number of teratons has been reduced to 00 tmes and apply the modfed proposal BOA and the BOA [] on the optmzaton problem n queston accordng to the parameters on Table. Runnng both optmzaton algorthms n 0 tmes and ther respectve results (objectve functon) s shown n Fg.. The fgure shows that by runnng the algorthm n fewer numbers of teratons, whch leads to a reducton n the executon tme of the algorthm, the modfed algorthm has a very desrable functonng. The average executon tme of the modfed BOA n 0 tmes of executon the algorthm s.s. The results ndcate that the modfed BOA has reached the optmum pont of ssue 6 tmes n every 0 tmes of executon the algorthm, and wth the average value of objectve functon equals to.6 n 0 tmes of executon the algorthm. The error n respect to the desred optmum pont s about 0.9%. In addton, n order to compare the functon of the modfed algorthm n ths artcle regardng the accuracy of the output results and the executon tme wth the nature-nspred algorthms lke as PSO and GA wth controllng parameters ncluded n Table, accompaned by ther output results and the executon tme of the algorthm shown on Table. By comparng the executon tme of the mentoned algorthms n Table and the accuracy of the output results, advantages of the proposed method n ths comparson are obvous. Table Controllng parameters for the BOA Number of Bats Intal loudness Intal rate of pulses Bounds of frequency < f <00 Table Controllng parameters for PSO and GA. Parameters of PSO Algorthm Number of swarm Number of teraton Personal Learnng Coeffcent Global Learnng Coeffcent Inerta Weght Parameters of Genetc Algorthm Populaton sze Number of generaton Intal populaton Mutaton Crossover functon C= C= w= random scattered Table Output results and the executon tme of the algorthms for case study. TSM PSO GA Modfed-B A TSM TSM TSM TSM TSM5 TSM6 TSM TSM TSM9 TSM0 TSM TSM TSM TSM Executon tme.6 s. s. s Objectve functon CASE STUDY In order to show the capablty of the proposed algorthm n solvng the ssue of optmal coordnaton of overcurrent relays, t has been appled on another busbars power (Fg. ). Kherollah and Namdar Optmal Coordnaton of Overcurrent Based on Modfed Bat Optmzaton Algorthm 6

5 Internatonal Electrcal Engneerng Journal (IEEJ) Fg. Runnng both optmzaton algorthms (modfed BOA and BOA) n 0 tmes for network #. Studed network ncludes transmsson lnes, transformers, and 6 drectonal overcurrent relays. All the overcurrent relays possess characterstcs that have been explaned n the prevous example. The parameters related to the transmsson lnes, transformers, generators, and also the actve and reactve loads are ncluded n Appendx B. Base voltage of the system s KV and ts base power s 00 MVA. Short crcut calculatons were carred out on the system and the results ncludng the short-crcut currents passng through man and backup relays for each occurrence of the three-phase short-crcut fault near the man relay are shown n Appendx C. parameters provded on Table, wth the teraton of 000 tmes. The results on 0 tmes of executon the algorthm on average are. and the tme of ths executon s 6.s. Then, n order to show the optmal functonng of the modfed algorthm, the number of teratons s reduced to 00 and the executon number for each of the algorthms s repeated for 0 tmes. Fgure shows the output results. The modfed proposal BOA has an average objectve functon of. and the executon tme s.s. In the second part, n order to compare the functonng of the proposed algorthm wth the nature-nspred algorthms lke as PSO and GA, wth regards to the accuracy of the results and the speed of runnng, they were beng appled to the optmzaton ssue of the coordnatng the overcurrent relays. Controllng parameter of the algorthms PSO and GA are the same as the prevous example. Table Output results and the executon tme of the algorthms for case study. v. RESULTS AND DISCUSSION Fg. -busbars power network. The desred functon of the proposed algorthm s provded n two parts due to the lower tme consumer n executon the algorthm and ncreased accuracy of the output results. In the frst part the BOA [] s appled to the ssue of optmzng the coordnaton n overcurrent relays wth the controllng Kherollah and Namdar TSM PSO GA Modfed-B A TSM TSM TSM TSM TSM5 TSM6 TSM TSM TSM9 TSM0 TSM TSM TSM TSM TSM TSM Executon tme.6 s 56.5 s. s Objectve functon.50.. Optmal Coordnaton of Overcurrent Based on Modfed Bat Optmzaton Algorthm

6 Internatonal Electrcal Engneerng Journal (IEEJ) The results are shown n Table. The accuracy of the results and the executon tme of the algorthms ndcate the superorty of the proposed algorthm n comparson to other algorthms. VI. CONCLUSION Optmal coordnatng of overcurrent relays n dstrbuton, sub-transmsson and transmsson networks s a crucal ssue n determnng the stablty and the relablty of a power system. Applyng optmzng algorthms to the ssues exstng n power networks leads to proftng and ncreasng the securty level of the networks. The executon tme of the algorthm and the accuracy of the results extracted from the algorthm are two determnng parameters n choosng the optmzaton algorthm n protectve functons. In ths artcle, a new modfed Bat Optmzaton Algorthm (BOA) has been appled to the optmal coordnaton of overcurrent relays problem. Results show the proposed method has sgnfcantly reduced the executon tme of the algorthm whle mprovng the accuracy of the output results n comparson wth the other nature-nspred algorthms lke as PSO and GA those prevously have been appled to the problem. Appendx A APPENDIX Short-crcut currents passng through the prmary and backup relays per every symmetrcal three phase short-crcut fault occurrng near the crcut breaker of the prmary relay for network #. No. of Current(A) No. of Current(A) prmary relays back up relays Appendx B The parameters of the transmsson lnes. Extreme Nodes The parameters of the transformers and generators. V(kV) X R Generator Transformer The amounts of actve and reactve loads. Appendx C R (Ohm/Km) Short-crcut currents passng through the prmary and backup relays per every symmetrcal three phase short-crcut fault occurrng near the crcut breaker of the prmary relay for network #. X (Ohm/Km) B/ (Mho/Km) Length (Km) e e e e e e e e-6 0 No. of BUS V MW (generated) MVAR (generated) MW (load) MVA (load).05 slack Prmary Secondary Kherollah and Namdar Optmal Coordnaton of Overcurrent Based on Modfed Bat Optmzaton Algorthm

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