Compatibility of tracer gases with oil/paper cable insulation

This paper describes the results of an investigation designed to evaluate the long-term compatibility of tracer gases with HPOF cable insulation in view of selecting one or several gases for the detection of leaks in underground cable networks. Accelerated aging was done on cable models with He, CF4, SF6, c-C4F8 and N2 gases dissolved in the oil. The aging was performed at 120°C with a voltage stress of 15 kv/mm and under a pressure of 238 kPa. The investigation included the observation of the dielectric losses variation with time, the measurement of the corona inception voltage, the ac breakdown of the samples as well as the detailed dissections of the cable models. The tests showed that the tracer gases other than helium performed at least as well as nitrogen, which has a long history of use in the field.