Modeling protection systems in smart active distribution grids for a performance analysis

Amit Dilip Patil (University of Passau); Hermann de Meer (University of Passau); Poul Heegaard (NTNU Trondheim); Bjarne Helvik (NTNU Trondheim)

Abstract

Distributed renewable energy sources increase the fault level of the distribution grid. This will impact the protection system, possibly causing misoperation, such as blinding, which increases the fault clearing time. High impedance faults draw low magnitudes of fault current, leading to delayed protection tripping and high fault clearing times. Communication-based adaptive protection systems may improve these fault clearing times by adapting the protection sensitivity to sense low fault currents. However, communication is susceptible to variable delays, which could also lead to long 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 have a detrimental impact on protection systems.