Analysis of Current Imbalance Effects on MOSAs for MVDC Breakers Through Short Circuit Current Test-Bed Simulation

The Metal Oxide Surge Arrester (MOSA) was developed for the purpose of overvoltage protection in electrical systems, protecting electrical equipment from overvoltage caused by lightning strikes, switching operations, and fault conditions. In the interrupting process of the MVDC Circuit Breaker, the MOSA encounters large fault currents and must endure significant thermal and dielectric stresses due to long duration conduction. The MOSA is designed with a parallel stack of Metal Oxide Varistors (MOV) to enable it to withstand high thermal capacity and significant dielectric stress. However, the parallel stack of the MOSA leads to current imbalances, resulting in thermal stress across the stacks and consequently degrading the performance of the MVDC Circuit Breaker. In this paper, a 42kV 9kA Short Circuit Current Test-bed for evaluating the performance of MOSA in MVDC circuit breakers was simulated using PSCAD/EMTDC software. Under conditions of current imbalance in MOSA, the study compared transient interruption voltage, interruption time, and absorbed energy based on the number of columns. The study analyzed the impact of column numbers on the interrupting performance of MVDC circuit breakers during the interrupting process.