In-service location of partial discharge sites in polymeric distribution cables using capacitive and inductive probes

The partial discharge (PD) site location capabilities of capacitive and inductive probes were compared, employing 25 kV XLPE insulated distribution cable specimens. The measurements were carried out primarily in a laboratory environment using a model distribution system, which consisted of different spliced cable lengths interconnected via circuit breakers and transformers; limited preliminary tests were also made under high ambient noise conditions in substations where the open-tray installations of cables provided free access to the surface of the cables to permit scanning with the probe sensors. All tests were performed on fully energized cables. The capacitive probes were found to perform adequately well, provided lire probes could be inserted beneath the helically wound concentric neutral of fire cable specimens; they functioned exceptionally well with unshielded splice joints. The inductive probes, which were applied ill the form of a coil over the cable, had the decided advantage in that the detection procedure could be performed directly over the concentric neutral of the cable. However, their discharge site locating capabilities were rendered virtually ineffective in the presence of high ambient interference in substations.