Effect of temperature on space charge behavior in epoxy resin under polarity reversal voltage

At high temperature and high electric field, the accumulation of space charge would take place in epoxy resin which is used in ultra-high voltage direct current (UHVDC) dry bushings. The space charge accumulated would distort electric field distribution in epoxy resin under polarity reversal voltage. The epoxy resin samples were cast in vacuum condition. At different temperatures, the epoxy resin was first applied negative poling field of -10 kV/mm, which was hold for 90 minutes, and then the electric field was reversed to positive poling field of +10 kV/mm within 60 s. The positive poling filed was also hold for 90 minutes. The space charge in the samples during polarity reversal was simultaneously measured per 1 s. Under the same electric field strength, the higher the temperature is, the more the homocharge accumulated in bulk of epoxy resin samples. The homocharge can't dissipate after the reversal, which would lead to redistribution of the electric field. The space charge contributes an image heterocharge on the electrodes, which increase the magnitude of charge peaks on the electrodes after the reversal. At low temperature, the electric field in the epoxy resin sample is always uniform during the reversal. At high temperature, the maximal electric field in the epoxy resin sample appears near the electrodes, which maximum is about 1.25 times the applied Laplacian field.