Technical reports-a new cable phenomenon

A hitherto unknown phenomenon was discovered while developing a novel type of medium-voltage cable. In an attempt to increase the operation voltage of plastic-insulated belted-type cables, breakdown tests were performed on cables using sandwich insulation, i.e. a dielectric-air-dielectric composite. It was found that if a nonwoven porous tape was applied to the cores, so that the interstices between the cores were partly filled with fibrous material, the breakdown voltage was significantly raised over the desired level corresponding to 30 years at 10 kV. Several tests, both at full reel lengths, of longer duration are reported that confirm this phenomenon. The phenomenon can be used for designing improved multicore medium-voltage cable and leads to novel conceptions of the behavior of internal discharges, especially in large cavities.<>