Voltage current based time inverse relay coordination for PV feed distribution systems

Abstract

Integration of distributed energy resources in distribution systems results in change in network topology and fault currents levels. Particularly in case of solar based distributed energy resources, the fault feeding capability is extremely poor and a very thin margin exists between their loading and fault feeding capabilities. The conventional time inverse over current relays may not accurately and quickly discriminate between the normal loading and fault conditions. This identified protection coordination problem is addressed in this research article, by developing a voltage current based time inverse relay. The operating principle of this proposed relay is based on reduction in nodal voltage and marginal rise in fault feeding capability of PV based distributed energy resource connected with distribution system. The protection coordination problem for voltage current based time inverse relay is formulated as a non-linear optimization problem. In this optimization problem, the fitness function is defined as summation of operating time of all primary relays and non-linear constraints are constituted with five decision variables like time dial setting, over current pickup, voltage pickup and relay parameters. The proposed protection coordination is simulated for 8 bus test system and solved with the help of evolutionary based optimization algorithm. The performance of the proposed voltage current based time inverse relay is compared with conventional relay and observed that their performances are superior to the conventional time inverse over current relays in term of their operating time.