A new concept for medium-voltage cables: improved voltage life of belt-type cables

Crosslinked polyethylene (XLPE) insulation has in many cases replaced paper insulation in medium-voltage cables. There is one important exception; in 10- or 11-kV networks in Europe an extremely efficient and simple paper-insulated cable is in use: the unscreened three-phase belt-type cable. This type of cable cannot easily be replaced by XLPE cable, because the required semiconducting screens make the XLPE cable expensive and its jointing more complicated. For this reason, an XLPE cable has recently been developed, designed as a three-phase cable, but without semiconducting screens. In the interstices between the cores of this cable, large discharges occur. However, the authors have discovered that these discharges can be decreased considerably by taping a fibrous material over the cores. In this way the life expectancy of this cable is substantially increased. A description is given of this entirely new phenomenon, and an explanation for the unexpected behavior of these interstice discharges is offered