Masato Mizokami

Vibration analysis of a 3-phase model transformer core

Noise generated by a transformer core has been reduced by improving material and design, but further reduction is still required. To obtain the reduction, the comprehension of noise generating mechanism is important. It is achieved by detailed investigation of core vibration. A vibration measuring system utilizing a laser Doppler vibration meter was developed, and the vibration of a 3-phase 3-limb transformer core was measured. The following results were obtained. The vibration on the front and 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 both of the side limbs. These results reveal that the principal cause of the vibration on the core was resonance. On the upper surface of the yoke, the vibration was higher in the right and left part and the middle. It is likely that the vibration on the right and left parts is derived from the magnetostriction of the side limbs. The vibration in the middle was considered to be generated by the magnetostriction under the rotational magnetization which occurs in the T-joint area of a 3-phase transformer core.

Harmonic analysis of AC magnetostriction measurements under non-sinusoidal excitation

A new system for analyzing ac magnetostriction of electrical steel sheets, has been developed. This system has the following advantages: (a) AC magnetostriction waveforms can be precisely measured up to 4 kHz, and analyzed to harmonic components. (b) Non-sinusoidal flux density can be excited to simulate the distorted waveform in an actual transformer core.