Breakdown characteristics and its mathematical model of oil-pressboard insulation under compound electric field

In order to study the breakdown characteristics of oil-pressboard insulation under compound electric field, the typical oil-pressboard insulating structure was taken as the study object. The breakdown characteristic of typical oil-pressboard insulation was obtained under compound electric field via breakdown tests at first. Then the electric fields in oil and oil-impregnated pressboard were simulated according to the equivalent circuit. The breakdown characteristic tests of oil and oil-impregnated pressboard were carried out separately under compound electric field. On the basis of the electric field mathematical expressions of the oil and oil-impregnated pressboard, the relationship between the electric field E and AC content (was got, and the electric field distribution in oil and oil-impregnated pressboard was compared with their breakdown strengths. And then the breakdown voltage mathematical expressions with AC content were concluded. The results showed that the main reason why the breakdown voltage of oil-pressboard insulating structure rises before and falls later is that the electric fields in the two materials vary with the AC content and there is difference in breakdown characteristics between two materials. © 2013 Chin. Soc. for Elec. Eng.