Controlling the Influence of an Asymmetric Air Gap in a Synchronous Electrical Machine on the Unidirectional Attractive Force

Asymmetry of the air gap in electrical machines impairs the output characteristics of both motors and generators. This asymmetry affects the magnetic induction at the poles and hence the pulsations of the electromotive force, current, and torque. The unidirectional attractive force of the rotor due to the asymmetry results in premature bearing failure and loss of the machine’s reliability. The causes and consequences of the rotor’s unidirectional attractive force are investigated, and analytical formulas are given for the asymmetry of the field and the magnetic attractive force.