The application of on-line PDM on in-service MV cable terminations

The majority of cable failures on distribution system is caused by the defects in cable terminations and cable joints. Failure mechanisms reported in cable accessories are predominantly involve partial discharge deterioration caused by voids, contaminants and workmanship problems. Therefore, partial discharge measurement (PDM) is an effective diagnostic preventing cable system failure. However, conventional PDM needs outage and time consumption, and it is not practice for routine test in field. Then on-line PDM is an alternative diagnostic. This paper utilizes electromagnetic field coupling mode for on-line PDM on MV cable terminations. Hence, the background noise, usually less than 40 Mhz in authorspsila experience, could be eliminated by means of using ultra-high frequency as mid-band frequency. A performance check of on-line PDM shows good agreement with conventional PDM. Among more then 5,000 cable terminations diagnosed by on-line PDM, there are about 200 cable terminations having PD signals. Disqualified cable terminations are dissected, and the defects and PD patterns have some relationships between them. Therefore, on-line PDM is practicable for cable termination diagnostics on-site.