Effects of the flux variations over the noise problem of series fractional horse power motors

The flux distributions in the air gap of the series fractional horsepower motors are composed of series space harmonics travelling at different speeds. The magnetic force at each point of the air gap varies with the square of the flux density. Forces of magnetic attraction act simultaneously upon diametrically opposite points of the stator and tend to distort the machine and cause noise. Noise, caused by the positively and negatively travelling waves of the force, can excite the motor mechanics around the resonances and cause the largest displacement of the stator assembly and loudest noise of the motor. The rotor eccentricity can also effect the flux distribution in the air gap and cause an additional noise