Comparative evaluation of dielectric strength of paper-oil insulation under ac, dc, combined, composite ac/dc and impulse voltages

Though paper-oil insulation is extensively used for EHV applications, there are many associated problems relating to the presence of dc component. The insulation is subjected to a dc component in addition to the average ac stresses that exist in the system. Under the combined ac/dc stresses, the behaviour of paper-oil insulation is not well understood. This paper attempts to study the breakdown characteristics of paper-oil insulation under combined and composite ac/dc voltages.