Research on Staged Relay Protection of DC Distribution System

Rapid and effective identification and isolation of DC faults is one of the key technical difficulties in the development of DC distribution networks. Compared with the traditional AC system, the DC power distribution system has the characteristics of "low damping". After a DC fault occurs, the fault current is very large, and the fault development process is extremely fast. Usually, the safety of the entire distribution network can be endangered within a few milliseconds. Through analyzing the bipolar short-circuit fault characteristics and typical fault current waveforms of symmetric unipolar DC systems, this paper proposes a phased overcurrent protection strategy based on current magnitude and a phased current rate-of-change protection strategy based on current change rate. This strategy uses single-ended current data without communication. The main protection can accurately identify the faulty line within 1 millisecond after the fault, which can meet the protection requirements of the DC distribution network for power supply in remote areas. The proposed protection scheme can identify faulty lines quickly and reliably, and meet the requirements of rapidity, selectivity and reliability of protection.