A DC Combined Apparatus for DC 1.5 kV Rail Transit Traction Systems

At present, short-circuit currents of rail transit DC traction system can reach more than 100 kA and bring serious damages to power equipment in the system. There is an urgent need for high-speed DC circuit breakers to isolate system short-circuit faults quickly. Recently, air-type DC circuit breakers are mainly used in the DC traction system of 1.5 kV rail transit. However, the air-type DC circuit breakers have the cons of long interruption time, large noise, large volume, and high price. The purpose of this paper is to design a novel DC combined apparatus with a rated voltage of 1.5 kV, a rated current of 4 kA, and a maximum breaking capacity of 100 kA. The DC combined apparatus is composed of a fuse and a forced zero-crossing vacuum switch in series, which can effectively interrupt the rated current, overload current, and short-circuit current in the DC traction system. The DC combined apparatus has the advantages of high electrical life, low on-state loss, small size, and low cost, and can significantly improve the reliability and stability of the DC traction system. It interrupts an overload current of 20 kA within 5.12 ms, and the breaking time of the prospective short-circuit current of 100 kA is less than 5.08 ms. Experimental results show that the DC combined apparatus can achieve the rated current, overload current, and short-circuit current interruptions in the DC traction system quickly and effectively.