DC Conductivity and Joule Heat Effect in the 320kV XLPE Cables

With the increased demand for long-distance power transmission, the high voltage direct current (HVDC) technology has developed rapidly. And the cross-linked polyethylene (XLPE) extruded cables as the key equipment play an important role in the HVDC transmission. In this paper, the influence of temperature and electrical field on the conductivity of the XLPE insulation was discussed. Besides, the relationship between the conductivity of XLPE and the temperature and electrical field was simulated. The relationship between the conductivity and temperature was described by Arrhenius equation. The conductivity-electrical field relationship was analyzed via the Poole-Frenkel model. The amount of Joule heat and temperature rise of the XLPE insulation used for 320kV voltage level was assessed using the developed conductivity model. The results show that the conductivity of the XLPE insulation increases about three orders for the temperature rising from 293K to 363K under the electric field increasing from 10kV/mm to 60 kV/mm. The temperature rise induced by the Joule heat of 500kV XLPE insulation is calculated to be 10K. The effect of temperature on the characteristics of the cable insulation such as conductivity, voltage withstand capability has to be accounted at type test of the cable system.