Application of Impulse Response Characteristics in Rail-ground Transition Resistance Measurement

Objective The stray current harm in urban rail transit lines is increasingly non-ignorable. Stray current is not easy to be detected, and the amount of the rail-ground transition resistance is a crucial factor affecting stray current. Therefore, measuring the amount of the rail-ground transition resistance is an effective stray current control method to judge the influence degree of stray current. Method Based on EMTP (electromagnetic transient program) software, a simulation model of the track circuit distributed parameters is built. The respective influence patterns of the distributed capacitance, distributed inductance, longitudinal resistance of the steel rail, and the rail-ground transition resistance on the time-varying characteristic curve of impulse impedance are obtained by using the single control variable method. The method of using impulse impedance time-varying ratio curve to judge whether the rail-ground transition resistance meets the requirement is proposed, and further verified by actual measurement of an urban rail transit line in Chengdu. Result & Conclusion Within 7~20 μs, only the rail-ground transition resistance parameter may affect the time-varying characteristics of the impulse impedance. Therefore, it can be used to reflect the condition of the rail-ground transition resistance and make valid judgement on whether the rail-ground transition resistance meets the requirement in the specification or not. Test results show that the measuring method is feasible and practical.