Effect of temperature and voltage application time on space charge decay of HDPE

Polyethylene is a material that is widely used as insulation for power cables. In this paper, the effect of temperature and voltage application time on space charge decay in HDPE is described. Negative charge was found to be retained by the samples when a field of 50kV/mm was applied at temperatures of 25 and 40 degC, with an amount that increased with increasing voltage application time. The same field applied for 4800s at 60degC gave both negative and positive space charge, but only positive charge at 90 degC The decay time of the negative charge increased as the amount of negative space charge retained after voltage removal increased. This indicates that much of the trapped negative charge could not be de-trapped easily. In contrast positive space charge was observed following the application of 180 kV/mm and 300kV/mm. The speed of positive charge decay in these cases was much faster than that of the negative charge accumulated under 50kV/mm. It was also observed that the decay time of positive charge decreased with increases in the cathode field measured just before short-circuiting at 25 and 40degC, but not at 60 and 90degC.