The cross-coupling AT (Autotransformer) power supply mode is applied on high-speed railways in China. When the power failure of traction substation is caused by the incoming power supply or equipment failure, the traction network needs to adopt the over-zone feeding operation condition to ensure the continuous power supply It is necessary to analyze the short circuit impedance of traction network under over-zone feeding operation condition. It provides a useful reference for the analysis of relay protection and power supply capacity of the traction network. In this paper, the equivalent circuit method is used to build the circuit model of cross-coupling AT power traction network under over-zone feeding operation condition, and the relationship between short circuit impedance and distance is deduced. The relation characteristics of short circuit impedance and distance is explained. The simulation result based on Matlab/Simulink shows that the application of equivalent circuits and the derivation of short circuit impedance formula are verified.

Impedance analysis; Over-zone feeding operation condition; Cross-coupling AT power supply; Equivalent circuit.