Threshold-free localized scheme for DC fault identification in multiterminal HVDC systems

Abstract

In the future grid scenario, the continuous operation of large-capacity remote power transmission over an augmented DC network is imperative for implementing a reliable multi-terminal high voltage direct current (MT-HVDC) grid or, alternatively, an MTDC grid. A fast and selective DC fault identification method with improved reliability eventually enhances the operational continuity and flexibility of the MTDC grid. Based on the V/I ratio of a current limiting reactor, this paper proposes a new non-unit protection scheme for DC fault identification without a threshold value setting. The DC fault is precisely identified in a span of three sampling intervals by the V/I ratios of four sampling instants. The selectivity of the proposed scheme is verified in a four-terminal MTDC grid. Simulation results demonstrate that the effective detection, discrimination, and location of a DC fault strictly satisfies the speed requirement (<1ms) with a location error of less than 1%. Moreover, the relevant sensitivity analyses reveal that the proposed scheme remains invariant for a wide range of fault locations and resistances and perform efficiently, even with a lower sampling frequency. In addition, transient events apart from DC faults fail to trigger the protection, indicating the high robustness of the proposed scheme.