抄録
In order to study the acoustic noise generated by transformer cores, the authors have made many 3-phase model transformers, and have measured the noise levels. A unique behavior was found in one result of the noise measurements. The clamping pressures of 0.15MPa and 0.30MPa were applied on the model transformers. In the case of 0.15MPa, the noise levels at the flux densities of 1.5T and 1.6T were unnaturally high in comparison with 0.30MPa. In addition, the harmonic components in high frequency range were higher in the noise spectra at those flux densities. Concerning about the cause of the noise increase, it was assumed that the irregular overlap made in the core joint by accident formed the gap between the core sheets, so that the impact at the end of the sheet was caused by the vibration generated by magnetic attractive force, consequently, impulse sound was generated. For more detailed study, the model core for the investigation on core joints was built. The irregular overlap was intentionally made in the joint, and the waveform of sound pressure was measured. The impulse sound appeared on the measured waveform.
