Costing energy savings for a dual-mode motor

An analysis is presented of energy savings realised for a fixed speed induction motor by using a dual-mode design. This uses a nonstandard divided stator winding allowing two alternative modes of connection of the winding sections, to be selected according to loading. Control is automatic using microprocessor and thyristor switches but alternatively manual control may be used. Power losses are reduced and soft starting is achieved. The paper presents measured power loss against load characteristics for both a conventional and a dual-mode motor that are identical except for the stator winding. Possible duty cycles are assumed and the resulting energy savings from adopting the dual-mode design in place of a conventional motor are calculated. A present value is attributed to the losses, allowing the cost effectiveness of the dual-mode motor, based on power savings alone, to be determined.