Methodology of on-site Precise Partial Discharge Measurement for Cable Terminations and Joints

Partial discharge (PD) measurement is a powerful technique for the insulation diagnosis and precise asset management of electric power apparatus. However, PD occurs sometimes not continuously, rather with very low repetition rate in its inception stage. In that case, it is difficult in on-site PD measurement and diagnosis, because the pulses of very low repetition rate are difficult to produce any finger print such as phase resolved PD pattern (PRPD pattern). On the contrary, the continuously generated pulse signals obtained at the on-site PD measurement sometimes do not come from PD generated at the internal electrical insulation layer but outside of the apparatus such as a surface of the bushing, an edge of a metallic part of the apparatus which is installed near the objective apparatus. These signals coming not from the intended apparatus sometimes leads incorrect diagnostic results. Thus, the discrimination methodology of PD signals occurring in the intended apparatus is important for the accurate PD measurement and diagnosis. This paper discusses the discrimination methodology for the PD measurement at cable terminations and joints.