Synchronous and asynchronous torques in squirrel-cage induction motors

Synchronous torques occurring in squirrel-cage induction motors may be due to a variety of causes, one of which is the interaction between pairs of stator and rotor harmonics. The paper includes an analytical treatment of the squirrel-cage rotor and applies this and the analysis of the doubly-fed cascade machine to the calculation of synchronous torques of this particular character. The concepts are extended to take account of the way in which a squirrel-cage rotor may provide coupling between stator harmonics of different orders during normal asynchronous operation of the machine, and an equivalent circuit for this is presented.