EFFECTS OF SLOT COMBINATION ON ACOUSTIC NOISE FROM INDUCTION-MOTORS

The electromagnetic force due to slot combination has a strong influen ce on acoustic noise from induction motors. When both the vibration mo de and natural frequency of the stator correspond to those of the elec tromagnetic force, the stator causes a resonance which results in a lo ud noise. Therefore, it is necessary to estimate accurately the electr omagnetic force before acoustic noise can be reduced. The force is cal culated numerically by a combination of transient magnetic field FEM a nalysis and harmonic analysis by using a Fourier series expansion. The moving of the rotor and eddy currents are also taken into account in the FEM method. The acoustic noise from three types of motors is measu red to verify the developed method. The simulated frequency and space harmonic order of the electromagnetic force are in good agreement with the measured frequency and vibration mode.