Analysis of overcurrent numerical-relays for protection of a stand-alone PV system

This paper presents an overcurrent protection scheme for a stand-alone PV system consisting of PV array, DCDC converter, DC-AC inverter, relay and circuit breaker to fed an irrigation load. This scheme is based on a numerical relay which is composed of rms current converter, integrator, comparator, low-pass filter and reset logic. The model of the system is simulated using MATLAB/Simulink. The performance of the relay is investigated at normal conditions, even during motor starting of the irrigation load as well as at faulty conditions. The relay succeeds to discriminate between the fault current and the starting current of the motor and operates only under faulty conditions.