Relay Protection Coordination for Photovoltaic Power Plant Connected on Distribution Network

Abstract

This paper presents a procedure and computation of relay protection coordination for a PV power plant connected to the distribution network. In recent years, the growing concern for environment preservation has caused expansion of photovoltaic PV power plants in distribution networks. Numerical computer simulation is an indispensable tool for studying photovoltaic (PV) systems protection coordination. In this paper, EasyPower computer program is used with the module Power Protector. Time-current relay curves will be computed and plotted for all protection devices in the network and the PV power plant. Protection relay AREVA Micom is placed on the secondary side of a 10 kV feeder and has overcurrent and ground fault protection. The HV side of the transformer station where a PV power plant is connected has an HV fuse. On the secondary side of the transformer there is a low-voltage (LV) circuit breaker Končar 400A with overcurrent, under/over voltage, under/over frequency and ground fault protection. Furthermore, the fuse in the supplying cable for the PV plant is installed as well as the LV breaker in the PV switchboard. Each SMA Tripod inverter is protected with the fuse and the RCD relay. All these relays are modeled and short circuit analysis is performed on several places in the network and the PV power plant and the transformer station. Three phase and single phase to ground faults were considered. Time-current plots were presented and a relay setting is suggested in order to satisfy selectivity and backup protection.