第4卷第6期 智能系统学报 Vol.4 No.6 2009年12月 CAAI Transactions on Intelligent Systems Dec.2009 doi:10.3969/j.issn.16734785.2009.06.014 Optimal coordination of directional over current relays using evolutionary programming M.Geethanjali,S.Mary Raja Slochanal (Department of Electrical and Electronics Engineering,Thiagarajar College of Engineering,Madurai-625015,India) Abstract:Co-ordination of directional over current relays (DOCR)requires the selection and setting of relays so as to se- quentially isolate only that portion of the power system where an abnormality has occurred.The problem of coordinating protective relays in electrical power systems consists of selecting suitable settings such that their fundamental protective function is met,given operational requirements of sensitivity,selectivity,reliability and speed.Directional over current relays are best suited for protection of an interconnected sub-station transmission system.One of the major problems asso- ciated with this type of protection is the difficulty in coordinating relays.To insure proper coordination,all the main/back up relay pairs must be determined.This paper presents an effective algorithm to determine the minimum number of break points and main/back up relay pairs using relative sequence matrix(RSM).A novel optimization technique based on ev- olutionary programming was developed using these main back up relay pairs for directional over current relay coordination in multi-loop networks.Since the problem has multi-optimum points,conventional mathematics based optimization tech- niques may sometimes fail.Hence evolutionary programming (EP)was used,as it is a stochastic multi-point search opti- mization algorithm capable of escaping from the local optimum problem,giving a better chance of reaching a global opti- mum.The method developed was tested on an existing 6 bus,7 line system and better results were obtained than with conventional methods. Keywords:power system protection;protection coordination;directional over current relay;evolution- ary programming;optimization technique CLC Number:TP18 Document code:A Article ID:1673-4785(2009)06-0549-12 The main function of power system protection is to Since it is very difficult to find a proper relay setting isolate only the faulty component or a minimal set of to meet the requirements by traditional methods,partial components as soon as the fault occurs.Since the main optimization of OC relay settings based on predetermined protection system may sometimes fail(relay fault or pick-up current settings were developedis6.Since they breaker fault),there must be back up either in the cannot take all system conditions into consideration the same station (local back up)or in neighboring lines results may get trapped at local optimum relay settings. (remote back up)with time delay according to the se-Therefore some of the different multi-point search algo- lectivity requirement.The determination of the time rithms such as genctic algorithms and evolutionary delays of all the back up relays,in the main/back up programming (EP)are used to reach global optimum in relay pairs,is known as coordination of the protection a better way.Thus recently the problem of coordinating system.Generally,in meshed networks with multiple DOCR in power systems was stated and solved in the generation buses,directional protection relays are framework of optimization theory.For this paper,a used.Among those,directional over current relays novel approach using EP for optimal coordination of (DOCR)are the major protection devices in distribu- DOCR was developed.The work done involved the fol- tion systems.The major problems associated with lowing two stages: DOCR are relay setting calculations and coordination. 1)Determination of a minimum set of break points Received Date:2008-11-24. and the main/back up relay pairs using relative se- Corresponding Author:M.Geethanjali.E-mail:mgeee@tce.edu. quence matrix (RSM)