Acoustic noise from small 2-pole single-phase induction machines

The radial magnetic force waves in small 2-pole single-phase induction machines are investigated analytically, taking into account the interaction of the homopolar flux-density waves and conventional flux-density waves. The analysis is verified by noise and vibration measurements. Experimental studies are made on the effects of the unbalance between the main and auxiliary fields on homopolar flux-density waves and on noise emission. The effects of a number of design changes on noise levels are also studied. These include a reduction in m.m.f. harmonics, minimising the dynamic unbalance of the rotor and reducing the magnetic permeance variations in the stator and rotor cores.