On the use of doped polyethylene as an insulating material for HVDC cables

The merits of HVDC power cables with polymeric insulation are well recognized. However, the development of such cables is still hampered due to problems resulting from the complicated dependence of the electrical conductivity of the polymer on the temperature and the DC electric field and the effects of space charge accumulation in this material. Different methods have been suggested to solve these problems yet none of these methods seem to give a conclusive solution. The present report provides a critical review of the previous works reported in the literature concerning the development of HVDC power cables with polymeric insulation. Different aspects of those works are examined and discussed. An account is given on an investigation using low density polyethylene (LDPE) doped with an inorganic additive as a candidate insulating material for HVDC power cables. Preliminary results from measurements of DC breakdown strength and insulation resistivity of both the undoped and the doped materials are presented. It is shown that the incorporation of an inorganic additive into LDPE has improved the performance of the doped material under polarity reversal DC conditions at room temperature. Moreover, the dependency of the insulation resistivity on temperature for the doped material appears to be beneficially modified.