On the common mode to differential mode transformation of conducted disturbance in double track traction lines

The common mode to differential mode transformation of rail currents and voltages normally present in double track railway systems is considered. Differential mode signals are a potential threat for a broad range of signalling circuits based on the track circuit principle. Operators´ and manufacturers´ attention is normally on exceptional losses of symmetry of the traction return circuit under fault or failure condition, but it is shown that a theoretical 9% transfer of the traction return current can occur on the opposite track under normal conditions.