Magnetostriction and the Influence of Higher Harmonics in the Magnetic Field

Knowing the effect of the higher harmonics of the magnetic field on the magnetostrictive behavior of electrical steel is highly beneficial for the noise aspects. In this work, the effect of a third harmonic with a variety of amplitudes and phase delays is extensively studied. Magnetostriction measurements are performed on samples of grain-oriented and nonoriented electrical steel under sinusoidal excitations with a third harmonic component and are compared with those of a purely sinusoidal excitation. The frequency spectrum of the measured data, where the second and the fourth harmonic are the most significant ones are then calculated. The measured data show that only knowing the amplitude of the third harmonic is not sufficient to estimate the variations of the magnetostriction. In fact the phase delay of such third harmonic can significantly alter the results. The measurements are carried out on two grain-oriented and two nonoriented samples under a magnetization with a fundamental of 1.3 T and 50 Hz, from which the following conclusions are drawn. Increasing the phase delay of a 8% third harmonic ratio from 0
$^{\circ}$
to 180
$^{\circ}$
delay, causes a variation up to 55% of the 100 Hz component for the two nonoriented materials. In the case of grain-oriented materials, up to 50% change is obtained. The measured data of the 200 Hz components show an increase, as well. However, since their values are far lower than the 100 Hz component, their effect is considerably smaller on the magnetostrictive behavior. These results are highly important for the noise of electrical machines and transformers, due to the magnetostriction phenomenon.