Deterioration of LPOF cable insulation due to ingress of SF6 gas

Abstract

Contamination of oil in low-pressure, oil-filled, paper-insulated, high-voltage cables connected to the high-pressure chambers of gas-insulated switchgear, due to the leakage of SF6 gas, have often been reported by electric power utilities. As a consequence this contamination can impair not only the dielectric behavior of oil and oil-paper composite but also the dielectric integrity of adjoining termination. This experimental investigation explores the impact of trace amounts of SF6 gas in oil on its dielectric strength under the power frequency and lightning impulses. The results show that minor leakages of SF6 gas improve the power frequency dielectric strength of oil. However, longer contact of gas with oil can significantly reduce it both under the power frequency as well as the lightning impulses of both polarities. Vaporization of liquid is found to cause pre-breakdown discharges which lead to its final breakdown.