On the thermal breakdown of AC cables and transformer bushings

Often, breakdown of cables and transformer bushings under ac conditions is believed to be due to thermal breakdown of the insulation in these equipment. Recently certain extensions to the theory of thermal breakdown have been proposed elsewhere while dealing with HVDC cables. The dielectric-loss mechanism being different in AC and DC cases, detailed examination of the proposed theory has been felt warranted. In this paper, the proposed theoretical extensions have been examined for their applicability to the case of alternating voltages. Interesting results are presented in the paper. The results have been, qualitatively, compared with relevant, published, results available in the literature and found to match reasonably.