Study on complex grounding fault protection with high-impedance for at feeding traction system

At present, for providing more technical-economic advantages, electric traction systems with a 2×25 kV AT (autotransformer) power supply are adopted currently for high speed and heavy duty railway lines in China. If the AT fed system occurs complex faults with interruption of the feeder wire between two ATs and one of the interrupted terminals grounding to earth in the same time. Complex faults have occurred many times on the Datong-Qinhuangdao double electric railway lines in China. Here, new principles of working criteria and the structure of protection relays for alleviation of these complex faults are proposed