Analytical Study on the Effect of Rotor Slot Skewing on the Parasitic Torques of the Squirrel Cage Induction Machine

This is the authors' abstract. We don't add key points for this paper.

Skewing of the rotor slot of a squirrel-cage induction machine has been commonly used since the beginning. However, little guidance is given regarding the principle of the working effect of the method, but even in such rare cases, the explanation does not cover the true physical reality. Consequently no formula exists for calculation of the effect. In this study, the principle of the working effect of the rotor’s skewing is derived in accordance with the true physics of the phenomenon, for both the synchronous and the asynchronous parasitic torque. The calculation regarding synchronous parasitic torque is based on comparing the stepped MMF curve of the straight rotor slot and the trapezoidal MMF curve of the skewed slot. New formulas are provided for both type of parasitic torques. Practical cases are investigated in details. Knowing the theory and the formula of slot skewing, the skew can now be applied on a targeted manner and in some cases, can completely eliminate the dangerous torque and noise components. Consequently, a theorem is formulated on when to skew according to the stator and when acc. to the rotor slot pitch; another theorem was found regarding residual synchronous parasitic torque after skewing. The investigation is then extended to include differential leakage attenuation calculations. With this in mind, from the point of view of rotor slot skew, the topic has been reviewed in its entirety.