Harmonics in the Squirrel Cage Induction Motor, Analytic Calculation Part II: Synchronous Parasitic Torques, Radial Magnetic Forces

Abstract

The magnetic field generated in the air gap of the cage asynchronous machine and the harmonics of the magnetomotive forces creating that magnetic field, as well as the synchronous parasitic torques, radial magnetic forces have been discussed in great detail in the literature, but always separately, for a long time. However, systematization of the phenomenon still awaits. Therefore, it is worth summarizing the completeness of the phenomena in a single study – with a new approach at the same time - in order to reveal the relationships between them. The role of rotor slot number is emphasized much more than before. New formulas derived for both synchronous torques and radial magnetic forces are used for further investigation. It will be shown that both phenomena in subject must be treated together. Formulas will be provided to take into account attenuation. Design guide will be provided to avoid dangerous rotor slot numbers. It will be shown that the generation of synchronous torques and radial magnetic forces do not depend – in this new approach - on the slot combination, but on the rotor slot number itself.

Keywords

• squirrel cage induction motor
• synchronous parasitic torques
• radial magnetic forces
• winding harmonics