Input impedance of chopper equipment and its significance in low-frequency track circuits

The authors review the disturbance mechanisms which can exist between chopper-controlled DC traction equipment and low-frequency track circuits which commonly operate at 50 or 60 Hz. They show that disturbance exists due to the various modes of chopper circuit operation, as well as to small mains-frequency AC voltage ripple sources which exist in the traction supply. Models are presented which define the sensitivity of single-rail and double-rail track circuits for these conditions. The authors also present an approximate model for determining the low-frequency input impedance of chopper equipment, for use in disturbance calculations.<>