Development of Short-Circuit Impedance Testing and Setting Calculation Device for Urban Rail Transit Catenary

Objective The line impedance of urban rail transit catenary is significantly affected by many factors such as wire material, line length, surrounding environment, etc., resulting in significant impedance differences between different lines and different time periods. However, in the setting calculation process, assessments often rely on empirical formulas, leading to inaccurate setting values and affecting the selectivity and sensitivity of the protection device. When the system encounters a short-circuit fault, false operation or refusal to operate may occur, posing a great safety hazard. Therefore, it is particularly important to develop a device that can accurately test the short-circuit impedance of the catenary and perform setting calculations. Method A low-voltage short-circuit test method is proposed. The method sets a short-circuit point at the end of the catenary and realizes the measurement of short-circuit impedance by applying low-voltage direct current at the head end of the line. A high-precision dual-channel synchronous sampling technology is used to obtain accurate sampling values of voltage and current, and a new method for solving line impedance by exponential curve fitting is developed based on RL （Reinforcement Learning）simplified bilateral power supply model and combined with Newton iteration method. In addition, by developing a software that integrates parameter configuration and setting calculation, the catenary impedance measurement and setting calculation device is successfully integrated. Result & Conclusion This device is not only capable of parameter configuration and line impedance solving, but also can simulate and analyze the current changes at the short-circuit point. It can realize real-time measurement according to different lines and environmental conditions, significantly improves the accuracy of line impedance measurement, providing solid data support and important reference for setting calculations. The accuracy of line impedance calculation and short-circuit current results is verified through actual examples, thus the feasibility and effectiveness of this method is fully proved.