A Review on Approaches Employed for Solving Directional Overcurrent Relays' Coordination Problem

The directional overcurrent relay (DOCR) coordination is considered as a highly constrained, nonlinear, and non-convex optimization problem. In order to find the optimum solution of these problems, many extensive efforts have been kept by the researchers. The optimum solution of directional overcurrent relay which coordination can be obtained by choosing proper time-current characteristic of DOCR, appropriate selection of objective function, and right selection of soft computing technique. This paper gives the insight into various approaches employed for DOCRs' coordination which are as optimization method-based approach, objective functionbased approach, and standard and non-standard relay characteristic-based approaches presented in the past literature. Also, this paper discusses mathematical formulation for overcurrent relay coordination.