Development of DC +/- 250 kV coaxially-integrated return conductor extruded insulation cable

摘要

This paper describes the development of +/-250 kV/300MW HVDC insulation-extruded cable with a coaxially-integrated return conductor, what is called a HVDC coaxial extruded cable, for monopolar transmission, where the return conductor is laid coaxially around the main cable core and insulated by an extruded return insulation. The features of the HVDC coaxial extruded cable give us both environmental and economic advantages as follows : (1) no risk of oil leakage, (2) no outer magnetic field theoretically, (3) higher design temperature than those of mass-impregnated (MI) cable and oil-filled (OF) cable, and (4) lower construction cost than that of two separate cables, i.e., the main and return cables. The development of the HVDC coaxial extruded cables is expected to give us a solution for the increasing need of HVDC cables with large power transmission capacity , environmental-friendly features and economic benefits. We have designed and manufactured the +/- 250kV/300MW HVDC coaxial extruded cables, factory joint and outdoor termination, based on the technologies and experiences of the usual type HVDC extruded cable up to 500kV and the HVDC coaxial extruded cables of +/- 120kV/54MW and +/- 250kV/180MW. The increase of the rated voltage and the power transmission capacity makes it difficult to design the return conductor and return insulation rather than the main insulation for the HVDC coaxial extruded cable. We confirmed that there was no significant problem of manufacturing and handling the cable, factory joint and outdoor termination. The results of the electric tests for the estimation of the initial electrical characteristics also show that they satisfied the required performance in both their main and return insulations.