Super synchronous motor

The name “super synchronous” has been given to a certain type of motor, not because the motor operates above synchronous speed but because it has the ability to develop super torque in starting. There has been a demand for a long time for some type of synchronous motor that would develop during the starting cycle a torque as great or greater than that of an induction motor of the wound-rotor, external-resistance type. The first applications of synchronous motors, where considerable starting torque was required, were accomplished by the use of friction clutches. A type of synchronous motor has also been developed, which in its design is quite closely an induction motor but having somewhat larger air gap and a secondary containing a larger amount of copper and wound with reference to the voltage at collector rings required for excitation. Such a motor involves the use of external resistance and changing the connections of the secondary from a polyphase starting net work to a singlephase synchronous field winding. It also inherently has lower efficiency, due to the higher core losses and the greater exciting energy required.