Optimum Coordination of Overcurrent Relays using Revised Simplex Method

The overcurrent relays (OCRs) are the major protection devices in a distribution system. To reduce the power outages, maloperation of the backup relays should be avoided, and therefore, OCR time coordination in power distribution network is a major concern of protection engineer. The OCR time coordination in ring fed distribution networks is a highly constrained optimization problem. The purpose is to find an optimum relay setting to minimize the time of operation of relays and at the same time, to avoid the maloperation of relays. The problem can be stated as a Linear Programming Problem (LPP).

This paper presents revised simplex method for optimum time coordination of OCRs in ring fed distribution systems. The LPP of OCR coordination involves large number of variables and constraints. As the revised simplex method works with the reduced table, the amount of computations and the memory requirement is very much reduced. Thus the calculations to be performed reduce to a great extent. Comparison with dual simplex, Big-M simplex and two phase simplex method is also presented.