Cogging torques in induction machines

Depending on the choice of design parameters, an induction machine can produce a cogging torque sufficiently high to give rise to locking at standstill. It is noted that the commonly used method of analysis of these torques, involving permeance waves, is strictly incorrect, and its use in conjunction with the ‘overlap’ method is inaccurate. The way in which cogging torques arise is discussed in terms of the energy associated with the magnetic field in the machine. A new method is described by which this torque variation can be determined from simple equations. Experiments on machines confirm the results of the analysis.