The research on the surface discharge intensity and its damage to the pressboard in oil-paper insulation under different hydraulic pressures

Abstract Almost all of the inside conducting components of a power transformer are insulated by oil and paper, which have crucial impact on the transformer’s safety. The degradation of oil-paper insulation is caused by discharge to a major extent, which is affected by hydraulic pressure to a large extent. In this work, the surface partial discharge in oil-paper insulation under different hydraulic pressures is carried out in a set of self-designed test device for the first time. Four discharge parameters were recorded with the help of a commercial partial discharge detector. The partial discharge inception voltage (PDIV) and breakdown voltage increased with pressure, but the rising rates decreased with the increasing of pressure. The difference between the breakdown voltage and the PDIV decreased initially and then increased at a tiny rate with the hydraulic pressure. The discharge parameters tended to decrease with the increase of pressure on the whole, and the average partial discharge value and partial discharge power decreased with no exception. The superficial phenomena and microstructure were displayed and compared to demonstrate the structure destruction caused by discharge. The chemical groups and element contents were observed to deduce the underlying principle of the change on the pressboards. These results are conducive to operating and maintaining oil-paper equipment in high-altitude areas. It also lays the foundation to reduce the size and weight of oil-paper insulation equipment by adjusting hydraulic pressure inside power transformers.