Evaluation of Semiconductor Based Methods for Fault Isolation on High Voltage DC Grids

This paper investigates methods for dc fault current fast interruption in high-power dc networks. A four terminal 1.2 GW dc transmission grid is used as a test system. The study compares four semiconductor-based devices for dc fault isolation: series hybrid dc breaker, half bridge and full bridge dc chopper, and LCL thyristor converter. The study considers performance of devices, costs and losses, and also application with larger dc grids. A hybrid dc CB has lowest losses, but the component sizing crucially depends on the speed of fault detection. It is demonstrated that fast communication between various devices in the dc grid is mandatory but might be very challenging. On the other hand, dc choppers and LCL converter component sizing is not dependent on the speed of protection, and there is no need for communication across dc grids. Additionally, they offer the capability of voltage stepping and dc cable power regulation. The LCL converter provides inherent fault current interruption and needs no overrating for dc faults. It also gives better efficiency compared to dc choppers. The performance of these dc breakers is demonstrated using detailed transient PSCAD simulation for dc faults.