Modeling Protection Systems in Smart Active Distribution Grids for a Performance Analysis

Distributed renewable energy sources increase the fault level in distribution grids, impacting protection systems and potentially causing misoperations like blinding, which increases the fault clearing time. High impedance faults result in low fault currents, further delaying protection tripping. Communication-based adaptive protection systems can improve protection sensitivity but are prone to delays, affecting fault clearing times. Therefore, this research addresses how the impact of distributed renewable energy sources, fault impedance and communication delay on protection systems can be quantified in terms of operation time. A discrete event simulation model is proposed to study protection performance in active distribution grids. Time distribution assumptions are investigated to capture the circuit breaker trip time accurately. The relative fault level of distribution and external grid is formalized. The impact of the relative fault level and communication delay on the protection system is determined by measuring fault clearing times using discrete event simulation. This impact is further quantified using a new protection performance index. Results show that for the system studied, protection blinding is critical for low impedance faults in grids with high fault levels, while high impedance faults are critical in grids with low fault levels. Moreover, sympathetic tripping is seen at increased distribution grid fault levels and fault impedance. Furthermore, while communication systems reduce fault clearing times, increased delays harm protection systems.