EMC between Class 390 trains and SSI on West Coast Main Line - Investigations and solutions

Insulated Gate Bipolar Transistor (IGBT) based traction drives were developed and introduced into service in the mid to late 90s; they typically operate in a switching frequency range above 1 kHz. They were used in new rolling stock in the expectation that they would avoid EMI problems with lineside signalling and telecoms equipment which had sometimes been experienced with the lower frequency (c. 400 Hz) gate turn-off thyristor devices used previously. The Class 390 (Pendolino) EMU uses IGBT drives and was introduced onto the West Coast Main Line as part of the route modernisation programme. The paper describes unforeseen EMI between the Class 390 and lineside Solid State Interlocking (SSI) systems and the consequent investigation of the detailed interference mechanisms involved. It then focuses on the identification and development of the necessary mitigation measures and their implementation. Of particular note is the development of an Isolating Surge Protection Unit (ISPU) which was successfully used to inhibit interference on SSI data links. Following the successful deployment of the ISPU and other mitigations, Class 390 trains obtained route acceptance and were successfully brought into fleet operation prior to introduction of the 125 mph timetable in September 2004.