変圧器通過故障遮断時の変圧器高周波短絡インダクタンス

Abstract

Currently, the IEC (International Electrotechnical Commission) standard (IEC62271-100) requires that the transformer limited fault (TLF) shall be verified in the test duty T10, the amplitude factor of which is defined as 1.7 for the transient recovery voltage (TRV). But, the TRV measurements for the TLF at various transformers show that the factor is mostly lower than 1.7. The reason for the low values is considered to be that the short-circuit inductance of transformer at the TRV frequency region is lower than that at the power frequency, and consequently the factor is lower than the standard value 1.7. But, the frequency-dependence of the short-circuit inductance of transformer has not been clarified yet. We measured the short-circuit inductances of model transformers with and without iron core. The short-circuit inductance with the iron core becomes small and equals to one without the iron core at the TRV frequency region. We concluded that this is the reason for the phenomena of low amplitude factor. In addition we showed, by taking eddy current within an iron core and Cu windings into consideration, that the frequency-dependence of the short-circuit inductance could be explained.