Effects of insulation and oil gap thickness on partial discharge characteristics of oil-impregnated paper insulation system for oil-filled cable

The effects of the insulation and oil gap thickness on the partial discharge (PD) characteristics of an oil-impregnated paper insulation system for oil-filled (OF) cables were investigated. The insulation of the test samples was composed of oil-impregnated papers and papers that had a hole. The papers were sandwiched between parallel plane electrodes. We first investigated the PD characteristics under AC electrical stress equivalent to 275 kV OF cables and the insulation thickness from about 1 to 2 mm with an oil gap having its thickness corresponding to 3 oil-impregnated papers. The PD characteristics, such as PD charge magnitude and repetition rate, were not much changed by the insulation thickness when PD occurred stably. In addition, we investigated the PD characteristics under the same AC electrical stress and the insulation with an oil gap having its thickness corresponding 2 to 5 oil-impregnated papers. The average maximum value of PD charge magnitude increased with increasing oil gap thickness.