Direct Measurement Combined with S Transform Based Fault Detection Method on Radial-bus Multi-terminal DC System

High voltage dc (HVDC) power system is a promising technology due to its easy integration in asynchronous networks and its high efficiency on long-distance transmission. However, its wide application faces the challenge of fault detection and protection. The rapid-growing dc fault current requires fast detection speed and sufficient discrimination between the fault condition and other transients. In this paper, a method combined with direct measurement on the dc current and S transform analysis is proposed. Basically, the direct measurement method monitors the moment when the current exceeds the threshold amplitude and S transform analysis is responsible for identifying whether the overcurrent is caused by a dc fault on the monitoring line. The effectiveness of this proposed method is tested on a 4-bus radial multi-terminal dc (MTDC) system in MATLAB/Simulink. The detection time and sensitivity with different fault resistances and locations are summarized. The sensitivity variation of different lines over the fault period is shown to support the validity of this method.