The railway environment is generally regarded as a ¡°severe¡± electromagnetic environment. For an electrified railway, Megawatts of power are required to be converted into the propulsion of trains in order to transport passengers or freight from one destination to another. The railway presents a complex electromagnetic environment made up of many systems including signaling, traction, telecommunications and radio communications.
Electromagnetic Compatibility (EMC) between electrical and electronic systems is an essential requirement for the reliable and safe operation of the railway. It is all too apparent that interference from traction power equipment may affect the signaling system with potentially dire consequences. The railway industry strives to reduce the risk of such incidents occurring through processes of hazard identification and risk mitigation. Electromagnetic compatibility forms an essential part of these processes.
The key EMC problem for the railway industry is the multi-use of the rail itself. In the 1840s the rails were simply a mechanical guidance system. The advent of electricity prompted the signaling engineer to invent train detection systems within track sections, involving using the rail as an electrical conductor. Today we have the situation where the rail is the guidance system, the return power conductor in ac or dc railway electrification schemes and is also being used as a conductor of low power level coded signals for the signaling system (track circuits). The interference problem is compounded by the introduction in recent years of inverter driven ac traction motor drives that have to be compatible with ¡°legacy¡± equipment.