Dependence of the dielectric properties of polyethylene insulation subject to water ingress with and without electrical aging

This paper reports on dielectric loss and dielectric strength measurements obtained on miniature cables soaked in water without voltage (hydrated) and under 5 kV rms voltage (aged). The dielectric losses were measured in polarization and depolarization using a Time Domain Spectroscopy (TDS) diagnostic system developed in-house. The dielectric strength of miniature cables under AC voltage was measured with the cable terminations immersed in a silicone oil bath. The test results showed that the dielectric loss increase solely depends on the water ingress in the insulation for a conditioning time ∼1000 h. Passed this threshold time, the dielectric loss increase is correlated to the maximum bow-tie tree length. The dielectric strength results are presented using a Weibull distribution and no correlation was observed between the breakdown values and the bow-tie tree lengths.