Magnetostrictive vibration of electrical steel sheets under a non-sinusoidal magnetizing condition

Magnetostrictive vibration of some electrical steel sheets magnetized with a pulse width modulated inverter has been presented. Magnetostrictive deformation was measured by a semiconductor strain gauge applied to specimens. The content of higher harmonics in the vibration was found tobe more than that included in the magnetic flux. High frequency magnetization superposed on that of low frequency yields a relatively large amount of the deformation in the specimen. In spite of a change of magnetizing frequency of the PWM inverter, some components of the vibration remained at particular frequencies. The cause of these high frequency vibrations was experimentally confirmed to be a shape resonance of the magnetostrictive vibration. Resonance modes were detected in a ring specimen and discussions were made with reference to theoretical mode analyses using finite element method. These results allow us to confirm that the magnetostriction in electrical steel sheets is one of the main causes of high frequency vibrations in electrical machines.