Vacuum circuit breakers for AC traction vehicles

GEC Traction has been involved with the design and manufacture of vehicle mounted vacuum circuit breakers (VCBs) for nearly twenty years. Situated on the roof near to the pantograph, this primary circuit breaker provides the locomotive or multiple-unit with protection against fault currents. It also isolates the vehicle whilst passing through earthed section gaps in the overhead catenary wire. This latter function accounts for the great majority of switching operations, there being, typically, on section gap every twenty kilometres on an inter-city 25 kV system. The author describes aspects of the latest VCB design, together with details of performance tests and the developments of a suitable high-strength polymeric insulator