Parallel transmission lines on the same corridor are commonly used in the transmission system. When a cross country fault occurs

the traditional fault phase selector may not correctly identify the fault phases due to the changes of fault characteristics. An algorithm for the calculation of the sequence currents at the fault point is proposed according to Thevenin's theorem and the sequence currents at the location of the protection relay are obtained with superposition principle. Finally

the formulas on the relation between sequence currents at the fault point are deduced. Based on the double-circuit transmission lines on the same tower without electrical connection at both ends

it is found that the applicability of the positive and negative sequence current phase selector is related to fault types under cross country non-earth fault conditions

while that under cross country earth fault conditions are related to fault types

mutual inductance as well as the ratio of equivalent zero sequence impedance and positive sequence impedance. In contrast

the phase selector based on the phase current difference change can correctly identify fault phases under different cross country fault conditions of parallel transmission lines on the same corridor. Simulation results based on the PSACD platform show that the analytical method for cross country fault is effective

and the analysis result of fault phase selector is correct. This work is supported by State Grid Corporation of China.