Optimal Protection Systems for Electric Power Networks

Abstract

Throughout the history of power system protection' improvements have continuously been made to most aspects of the protection system. However' the selection of type and characteristics of the protective relay are still carried out by specialists based on their experience. Since the applied design methods are strongly impacted by the personal philosophy of the designer' most of the existing protection systems are not optimal. In this paper' a new method will be presented to achieve an optimal protection system for an arbitrary network configuration' based on graph-Theoretical tools.an example. In this simple case' a selective protection only requires an overcurrent definite-time function for each relay location. In this case' relays rj' rj and r4 do not backup any relays' and can be adjusted for the shortest operation time (without delay). But relay r3 must take over the function of backup for r^ and rj-Therefore to achieve selectivity' r^ must operate after rj and r'. This can be realized by adding a time delay (i.e. zc=0.3 sec.) to ry In the same way' r^ should operate after ry and needs an additional delay of at least 2. © 1998 Institute of Electrical and Electronics Engineers Inc. All Rights Reserved.