Statistical study of resonance in AC traction systems equipped with Steinmetz circuit

Abstract

AC traction systems can be 25kV/50Hz single-phase, non-linear, time-varying loads of random nature causing unbalance and distortion of the supply voltages. To reduce voltage unbalance, thyristor controlled reactances are usually delta-connected with traction systems. This setup, called Steinmetz circuit, can adapt reactance values to traction load fluctuations in order to balance consumed currents. To avoid voltage distortion problems due to harmonic currents injected by traction loads, resonances between the Steinmetz and supply system reactances “observed” from the traction system must be analyzed. This paper characterizes stochastic behavior of these resonances, which is caused by random variations in traction power consumption. The study used simulations of an AC traction system with intercity services and measurements of a French railway traction substation.