Optimal Overcurrent relays coordination using genetic algorithm

For optimal co-ordination of Overcurrent (OC) relays, linear programming techniques such as simplex, two-phase simplex and dual simplex are used. Another way of optimal coordination program is using artificial intelligent system such as genetic algorithm (GA). In this paper a new approach will be used for optimal coordination of OC relays based on genetic algorithm. In this work we take into account both time setting multiplier (TSM) and plug setting multiplier (PSM) of OC relays in optimization procedure. Most OC relays accept only discrete values as TSM and PSM, and you should change your final answers to discrete form and this may corrupt the optimization. In this paper the act of quantizing the answers is taken into account as a part of optimization procedure, so the outputs are optimized discrete TSM’s and PSM’s. In other words the novelty of the paper is taking into account the PSM in addition to TSM to handle miscoordination problems both for continues and discrete TSM and PSM. The results obtained are quite encouraging and will be useful as an effective tool for coordination OC relays.

I. Introduction

During the operation of a modern interconnected Power system, abnormal conditions (faults, overload, over-voltage, under-frequency, etc.) can frequently occur. Such conditions cause interruption of the supply, and may damage the equipments connected to the system, arising the importance of designing a reliable protective system. In order to achieve such reliability, a back-up protective scheme is provided to act as the second line of defense in case of any failure in the primary protection (the first line of defense). To insure reliability of the protective system, the back-up scheme shouldn't come in to action unless the primary (main) fails to take the appropriate action. In other words, it should operate after a certain time delay known as coordination time interval (CTI), giving the chance for the primary protection to operate. The fore mentioned situation leads to the formulation of the well-known protective relay setting coordination, that consists of the selection of a suitable setting of each relay such that their fundamental protective function is met under the desirable qualities of protective relaying, namely sensitivity, selectivity, reliability, and speed[1].