Temporal Transition of Partial Discharge Characteristics in XLPE Cable Joint Model Taking Account of Long-Term Operation and Deterioration

The aging defect in the pre-fabrication type XLPE cable termination still can appear at the interface between the stress-relief cone (SRC) and XLPE insulation, or the interface between SRC and the epoxy resin receptacle, even in a good installation process. It is also reported that the aging defect, i.e., deposits would be due to the deoiling of the silicone grease or oil, exuding chemical additives such as vulcanizing additives from SRC, from dismantlement observation of the decommissioned XLPE terminations. Such defects might easily ignite partial discharge (PD) combined with the formation of the delamination due to the thermal stress under its operation and finally lead to failure. In this paper, PD characteristics are discussed for the XLPE cable termination using void defect model. Then, an epoxy resin mixed with barium titanate is injected to the interface of the SRC and the XLPE cable, and its PD characteristics are investigated. Barium titanate is one of the highest ferroelectric materials and considered to be a suitable material to simulate the aging deposit. The PD characteristics are discussed from viewpoints of the number of pulses, maximum charge and PRPD pattern. From the experiment, it is revealed that barium titanate layer can affect electric field behaviour inside the SRC interface with the relatively stable condition of PD occurrence during observation, especially in the border area of semiconductive and insulation of the SRC.