HV cables at the turn of the century

HV cable technology is characterized by a change over from the conventional lapped paper dielectric impregnated with oil under pressure to extruded synthetic dielectrics. Thermoplastic polyethylene and crosslinked polyethylene (XLPE) are increasingly used at higher and higher voltage levels because of favorable properties (low dielectric losses, simple maintenance, elimination of impregnant etc.). XLPE is used extensively in most countries up to 170 kV. Extensive development work and testing has lead to a breakthrough for this technology at the maximum service voltages for underground cable systems, i.e. 420 kV in France, Denmark and Germany and 525 kV in Japan. A challenging aspect in this connection has been the development of feasible joints and terminations. The technological evolution for submarine power cables has been more conservative than underground cables. The obvious reason for this is that the high cost of eventual subsea maintenance work leads to a preference for well proven technology based upon long time service experience. The trend has consequently been that the voltage level at which extruded dielectrics are used in submarine power cables is lagging in relation to maximum feasible voltage levels for underground cables. For HVDC cables the extruded dielectric is so far not technically feasible for the highest DC voltages, however, it is expected that such cable systems will be introduced in the near future for submarine applications