Comparative experimental study of dielectric strength of oil-cellulose insulation for mineral and vegetable-based oils

In this paper the results of experimental investigation on breakdown strength under AC and BIL voltage of impregnated cellulose elements in combination with oil gaps are presented. Within investigated two models three different types of breakdowns are generated: through bulk oil gap, over oil-pressboard interface (creep breakdown) and puncture breakdowns of paper insulation. In each experiment mineral oil insulation system was compared with vegetable-based oil (VBO) system. It is observed that for used composite models these two oils differ not only in breakdown voltages but also in breakdown types.