Surface discharges within oil insulated apparatus

Liquid insulation, mainly in the form of mineral oil, is a critical component of many different items of plant within electricity transmission and distribution systems-cables, bushings, switchgear, transformers. Usually it is in combination with solid insulation. This may take the form of paper impregnated with oil, such as in cables or bushings, resin impregnated components such as drive rods in tapchangers, or solid pressboard insulation to break up oil gaps, such as the barriers in transformers. Therefore, when one considers the effect of oil breakdown in oil filled equipment, one should consider the interactions which electrical discharges may have with solid surfaces. These are often the weak points of such systems. This paper is mainly concerned with the surfaces of barriers within transformers