Effect of Temperature and Voltage Application Time on Space Charge Decay of LDPE and HDPE

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Polyethylene is widely used as insulation for power cables. In this paper, the effect of temperature and voltage application time on the decay of space charge in LDPE and HDPE is described. When the applied voltage of 18kV was removed negative space charge was mainly found in the bulk region of the LDPE samples, whereas positive space charge was predominantly observed in HDPE samples. The space charge decay time in LDPE was shorter than that in HDPE suggesting that trapped positive charge was not de-trapped easily in HDPE. The space charge decay time also decreased with increasing magnitude of the anode (LDPE) and cathode (HDPE) field measured just before voltage was removed. The value of the apparent activation energy of space charge decay was estimated from the Arrhenius plot of the relaxation time of the residual space charge was found to be larger in HDPE than in LDPE. It is suggested that the trap level of positive charge in HDPE was deeper than that of negative charge in LDPE.
2010-06-01