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For precise evaluations of magnetostriction properties, a new magnetostriction measuring system using a laser vibrometer was developed. Frequency analysis of magnetostriction under non-sinusoidal magnetization revealed a nonlinear relation between harmonics in flux and those in magnetostriction. Transformer core vibration was investigated in order to clarify the relations between magnetostriction and transformer noise and to realize low-noise transformers. Resonance was proved to have an important role for core vibration. Domain-refined, grain-oriented electrical steel, which fulfills low loss and low magnetostriction properties simultaneously, is also explained.

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Noise produced by a transformer core has been reduced by improving material and design of the, core. Further reduction is required for the trend toward amenity. The comprehension of the mechanism producing noise is necessary and one of the measures is detail investigation of core vibration. We developed the vibration measuring system utilizing a laser Doppler vibration meter and we measured the vibration of a 3-phase 3-limb transformer core. The vibration on the front and the back of the core was two or three times higher than the other surfaces. The vibration occurred mainly in the limbs of the core and the vibration direction was perpendicular to the core surface. The vibration waveforms were out of phase between the center limb and the both side limbs. These results reveal that it is resonant vibration of the core. In the upper surface of the yoke the vibration was higher on the both sides and the center. It is supposed that the vibration on the both sides is derived from the magnetostriction of the limb and the vibration in the center is produced by the magnetostriction under the condition of the rotational induction which occurs in the T-joint of the core.T. IEE Japan, Vol. 116-A, No . 8,'96