Locating and Isolating DC Faults in Multi-Terminal DC Systems

TLDR

A multi‑terminal DC system composed of voltage‑source converters is highly vulnerable to a DC fault that can paralyze all converters until the fault is cleared. The paper proposes using the existing AC circuit breakers to extinguish DC fault current, thereby avoiding expensive DC circuit breakers. To isolate the faulted DC line, the method first identifies the faulted line and then uses fast DC switches to disconnect it before re‑closing the AC breakers to restore the system. The handshaking method successfully locates and isolates the faulted DC line and restores the MTDC network without requiring telecommunication.

Abstract

A VSC-MTDC (multi-terminal dc) system consists of voltage-source converters (VSCs) connected to a dc network at their dc terminals. The MTDC is most vulnerable to a dc fault which paralyses all the VSCs until the dc fault is cleared. As dc circuit breakers are expensive, this paper proposes a solution based on extinguishing the dc fault current by opening all the ac-circuit breakers (ac-CBs) which the VSCs are already equipped with on the ac-sides. However, it is necessary to identify which dc line is the faulted line (in case it is a permanent fault) so that it can be isolated by fast dc switches (which are much more economical than the dc circuit breakers), prior to restoring the MTDC system by re-closing all the ac-CBs. This paper presents the handshaking method, which locates and isolates the faulted dc line and restores the MTDC without telecommunication.