Dielectric Loss Characteristics of Oil Filled Cable Insulation Impregnated by Extremely Bad Tanδ Oil

In spite of being extremely large value of oil tandelta (several ten % of tandelta for example) in some oil filled (OF) cable splice box etc, there has been no such an event as a thermal breakdown due to dielectric loss up to the present. Therefore we examined the tandelta characteristics of OF cable insulation impregnated by extremely bad tandelta oil in detail. As a result, it turned out that the tandelta suppression effect by the following two reasons had acted, and was verified in the real use OF cable splice box insulation flowed by bad tandelta oil. (1) Tandelta decrease in high electrical stress (including operating stress of OF cable) region by so-called Garton effect which is related with the ion mobility of oil. (2) Tandelta decrease due to the absorption of ionic substance in oil to the insulating paper. The two above-mentioned effects are larger in the mineral oil than in the alkyl-benzene oil