Influence of the Pole Number on the Magnetic Noise of Electrical Ac Machines

This paper deals with the influence of the AC machine pole number on vibrations and noise of electromagnetic origin. First, rules of design of AC machines are reminded, pointing out the influence of the pole number. Then, the origin of magnetic vibrations and noise is explained. Analytical mechanical relations are given, allowing to estimate vibrations and noise of a machine. After that, the influence of the pole number is studied: on the machine radius, on the stator deformations, on the mechanical resonance frequencies and on the noise. The conclusions underline that machines with high pole number have stator vibrations of high amplitude. Calculations compare three machines with different pole number and fed at different frequencies. The conclusion is that, at the same speed and working power, machines with high pole number fed at high frequency are noisier than those with low number of poles fed at low frequency. Practical experiments illustrate these theoretical considerations.