Breakdown Characteristics of the Oil-Pressboard Insulation under Compound Electric Field

In order to study the breakdown characteristics of oil-paper insulation under compound electric field, the typical oil-pressboard insulation model was adopted according to the insulation structure in converter transformer. The electric field in oil and oil-impregnated pressboard was simulated according to the equivalent circuit for the above model, and the breakdown characteristic test for typical oil-pressboard insulation, oil and oil-impregnated pressboard was carried out separately under compound electric field. To analyze the relationship between the breakdown strength and electric field, the electric field expressions for oil gap and the oil-impregnated pressboard were derived under compound voltage with different AC content. The test result shows that breakdown voltage of oil-pressboard insulation rises first and falls later under compound voltage. According to the characteristics the electric field distribution and breakdown strength of oil gap and oil-impregnated pressboard, it can be found that the breakdown strength of oil-pressboard insulation mainly depends on electric field distribution and breakdown characteristics of oil and oil-impregnated pressboard under compound voltage.