Study on DC Flashover Characteristics of Oil-paper Interface under Uniform Electric Field

The flashover characteristics of oil-solid interfaces at a quasi-uniform electric field distribution were studied. The effects of the surface roughness, the material conductivity and the electrode distance were investigated. The increase in interface roughness led to a slight increase of the flashover voltage. The flashover voltages of the samples with different solid materials showed a correlation with the material conductivities. Moreover, comparing with pure oil, the DC flashover field strength at the oil-solid interface showed a minimum value when the electrode distance was around 5 mm, and it tended to be stable at a large electrode gap. This indicated that the charge migration played an important role when the electrode distance was small. Combining with further understanding of the charge transportation and distribution, the flashover field strength over a large electrode gap may be used as the criterion for insulation design of converter transformers.