THE ELECTRICAL PROPERTIES ALONG THE RADIAL DISTRIBUTION OF 500kV DC CABLE INSULATION

The electrical properties along the radial distribution of 500kV dc cable insulation play an important role in cable design, especially for the cable and accessory matching. Here we investigate the conductivity space charge density and breakdown strength along the radial distribution. The conductivity for the middle portion is slightly higher compared with that for the middle and outer portion for the un-degassing HVDC cable. The space charge density under low electric field is obviously reduced, but the effect under high electric field is not obvious after 60 days of degassing. Breakdown strength increases and then decreases from the inner to outer portion. In general, the change of conductivity and breakdown strength along the radial distribution is not obvious. In contrast, the HVDC cable after degassing shows different trend. With the increase of degassing time from 0 to 1440 hours, the conductivity of the insulation gradually decreases from the inner to the outer portion along the radial direction. Breakdown field strength shows a trend of gradual increment from the inner portion to the outer portion.