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

• AC traction systems can be single-phase, non-linear, time-varying loads.
• They are capable of unbalancing and distorting voltages.
• Thyristor controlled Steinmetz circuit is connected with traction systems.
• Resonances between the Steinmetz and supply system reactances must be analyzed.
• The paper studies these resonances by characterizing their stochastic behavior.

AC traction systems can be 25 kV/50 Hz 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.