Effects of rotor eccentricity on acoustic noise from induction machines

The variations of acoustic-noise power radiated from electric machines, having varying degrees of eccentricity of the rotor in the stator bore, were studied using a specially constructed rig in an anechoic chamber. A series of noise components, which were found in experiments to vary considerably with rotor eccentricity, were identified analytically from the expressions for the mode numbers and frequencies of the magnetic-force waves, taking into account the stator and rotor slotting, eccentricity and iron saturation. A method is presented for calculating the variation of important noise components with eccentricity. The effects on the noise power of different numbers of stator parallel paths and of different ways of connecting them were investigated using specially wound machines. Information is given concerning the choice of parallel paths and connections for noise reduction.