Dynamoelectric Stage

a device consisting of two ormore electric machines that are interconnected mechanicallyand electrically, or only electrically. It is used to provide smoothand economical control of the speed of rotation of an electricmotor (usually an induction motor) in medium- and high-powernonreversible electric drives. The speed is controlled by alteringthe booster electromotive force in the rotor circuit of the induc-tion motor that is developed by one or more DC or AC com-mutator machines. In a constant-power dynamoelectric stage (P = const.) one of the auxiliary machines is connected me-chanically to the shaft of the main motor. In constant-torquestages (T = const.) there is no mechanical connection and, instead of a single auxiliary machine, two are used, one of whichmay be an AC or DC commutator machine or a converter (ro-tary converter, ionic converter, and so on). The latter convertsthe slip energy of the induction motor into DC electric power, which is then converted into mechanical energy by the DC ma-chine and returned to the shaft of the stage.