Design of Modular Fault Current Limiter to Avoid Reliability Degradation

With the short circuit level increase in power grids, there is a need to increase rating of switch type fault current limiters (STFCLs), therefore, modularization of STFCLs is inevitable. This paper presents a comparative reliability analysis between the modular and non-modular STFCL topologies. It is demonstrated that modular design causes a considerable reduction in reliability. The aim of the presented study is to increase the reliability of modular fault current limiters using thermal management. The failure rate of STFCL module and junction temperature calculation is developed. The mean time to failure (MTTF) is used as the reliability metric. MTTFs of two topologies are calculated and compared. It is demonstrated that reliability of STFCL depends on the junction temperature of the semiconductor switches in the steady state, that it can be controlled by the thermal resistance of the heat sink. Ranges of the junction temperature and thermal resistance in which the modular configuration is more reliable are formulated. Then numerical studies are presented to verify the efficacy of the proposed approach.