Measurement of magnetostriction using dual laser heterodyne interferometers : experimental challenges and preliminary results

Vibrations and noise of electrical machines and transformers may be caused by Lorentz forces and/or by magnetostriction. Here we only focus on the vibrations and noise due to magnetostriction. Electrical machines and transformers have magnetic cores of ferromagnetic material. Magnetostriction can be seen as a reaction of the ferromagnetic material to the presence of a magnetic field in the material and it leads to unwanted noise. The magnetostriction varies from material to material and is dependent on the magnetic field (or the magnetic induction) and on external stresses applied to the material. For every different material, the magnetostriction properties have to be obtained experimentally, usually by means of magnetostriction strain measurements. In the past a measurement set-up using strain gauges was developed at the Electrical Energy Laboratory (EELAB). In this paper a new magnetostriction measurement set-up using a dual laser heterodyne interferometer is proposed which avoids the drawbacks of the strain gauge set-up. The preliminary measurements already show some promising results. The experimental challenges and future work are explained at the end