Determination of the No-Load Currents and the Associated Winding and Iron-Core Forces of Saturable Induction Machines for Sinusoidal and Nonsinusoidal Terminal Voltages

The most troublesome noise of electromagnetic origin in induction machines, the so-called magnetic noise, can be traced to radial forces and — in a much smaller measure — to tangential forces which occur when the air gap flux contains harmonic fluxes with pole pairs differing by a small integer. Such higher harmonic fluxes in the air gap are practically unavoidable and inherent in the design of induction machines. These fluxes are caused by the finite number of slots and phase belts as well as by saturation and eccentricity resulting in a nonuniform permeance of the air gap. The radial and possibly tangential forces originating in the harmonic fluxes set the iron core into vibration [1] and the noise caused by these force waves is generally in the frequency range of 500 to 3000 Hz, i.e., in the range where the human ear is most sensitive.