Correlation between AC breakdown strength and low frequency dielectric loss of water tree aged XLPE cables

This paper describes experiments performed on laboratory aged 12kV and service aged 24 kV XLPE cable samples. Results from measurements of residual ac breakdown strength, degree of water treeing and dissipation factors are presented. The dissipation factor at low frequencies was determined by both time and frequency domain measurements. Relation between these methods are discussed, and it is shown that both can be used for assessing the average ageing state of the cable. The results show that water treeing causes reduced residual ac breakdown strength, high and non-linearly increasing low-frequency dielectric loss.