An induction motor with paralleled rotor and stator

A LITTLE known method of operating induction motors is to parallel the rotor and stator windings. When this is done the pull-out torque as a motor is approximately doubled and the continuous horsepower output may be increased; as an induction generator, the maximum kva. output is increased. The machine may be operated simultaneously as a motor and as a generator. For heavy loads the efficiency is higher than that of the same motor operated with its sliprings short-circuited; and if the motor is to operate over a wide range, maximum efficiency may be secured by using a switching arrangement to short-circuit the rings at light load.