Stepper motor drive for on load tapchanger in electric locomotive

Indian Railways have a fleet of 2200 electrical locomotives running on 25 kV AC traction. An on-load tap changer is used to select the voltage for the speed control of DC traction motors. A four stroke reciprocating type air motor is presently used to drive the tap changer. A complex gear and camshaft mechanism is used to move the tap changer and to generate various logic signals for safe locomotive operation. The annual failure rate for such tap changers and their drives is of the order of 20%. A microprocessor-controlled stepper motor drive has been designed and constructed to drive the on-load tap changer. A current-controlled chopper is used to drive the motor and control logic has been generated through an optimum hardware and software combination. This assembly has been tested on a prototype tap changer in the laboratory.