Ensuring inverter drives do not present a signalling safety hazard-the solution

The author describes how the essence of compatibility between any traction power electronic equipment and signalling system which share a conductive path through the running rail is based on two principles: (i) signalling frequency avoidance; and only when this is impossible, (ii) signalling frequency minimisation. In the case of inverter propulsion drives the variable frequency nature of the equipment makes the task of ensuring compatibility more complex than for other forms of drive. Consequently, the author considers AC and DC supplied equipments separately