Protective relays on Pa. locomotives

No current rupturing device is provided between pantograph and main transformer on electric locomotives recently placed in operation on the Pennsylvania Railroad; instead a “pantograph relay” is used which is connected so as to utilize the substation circuit breakers to open high voltage short circuits, grounds, or overloads on the locomotive. A voltage relay is used to change the field strength of the traction motors at a predetermined speed, and slip relays provide protection against wheel slippage.