Magnetostriction and its relation to the no-load noise of power transformers

In this study, the magnetostrictive properties of grain-oriented electrical steel (GOES) are evaluated and their effect on the model transformers' core noise is presented. One main source of a power transformer's (PT) no-load noise is the magnetostrictive vibration of the magnetic core built with stacked GOES sheets. With an in-house coil measurement system (CMS), the magnetostrictive properties of GOES coils up to six tons were determined. The investigation resulted in the identification of GOES material with very low magnetostriction. Compared to a common low noise material, proved with transformer noise measurements, the newly identified material had an even better magnetostrictive performance. Out of two GOES coils, with different magnetostrictive properties, in total eight model transformers were manufactured. An analysis of the measured magnetostrictive properties of the selected GOES coils is provided with a focus on their relation to the no-load noise of PTs. The correlation between the GOES coils magnetostrictive properties and the model transformers sound pressure levels is evaluated. Performances of the measured magnetostrictive properties of the selected GOES coils are compared and a first relation to the emitted sound pressure levels of the manufactured model transformers is confirmed.