Effect of Voltage Reversal on Space Charge and Transient Field in LDPE Films under Temperature Gradient

Voltage reversal will strongly affect the stability of cable in service, especially under temperature gradient due to the temperature rise of the cable. In this paper, the results of space charge profiles and field distortions in low density polyethylene (LDPE) films after dc pre-stress of 50 kV/mm for 2 h under temperature gradient and then during different voltage reverse polarities or during different voltage reverse periods were presented. The test results show that the charge accumulation and field distortion are different under different voltage polarities due to the dependence of charge injection on electrode materials. In this work, under the Al / SC (Semiconductive) electrode system with a temperature difference of 40 degrees C, the maximal transient field occurs near the low temperature Al electrode when polarity varies from negative to positive while near the high temperature SC electrode when polarity varies from positive to negative. In addition, the faster the voltage reversal at room temperature the higher the maximal transient field, but the faster the voltage reversal the lower the maximal transient field under temperature gradient. Moreover, the maximal field appears during voltage inversion at room temperature while appears at pre-stress under temperature gradient.