Abstract

In high voltage cables, polyethylene is widely used as the insulation. With temperature, the physicochemical properties of polyethylene are gradually changed through thermal ageing mechanisms. In this paper, experiments were carried out to explore the effect of a thermally aged surface of polyethylene blend (HDPE/LDPE) films on the space charge and charge transport dynamics in the bulk associated with positive and negative charge injection. Thermal treatment was used to treat one surface of the specimens, which was exposed to air at a high temperature for various short times. The rate of oxidation on the surface was determined by the ATR-FTIR technique. The pulsed electroacoustic (PEA) technique and DC conductivity were used to investigate space charge and charge transport dynamics respectively. It was found that the oxidized surface resulted in a significant changes in the amount of accumulated space charge and the DC conductivity initially decreased below that of the reference sample. However, a severely oxidized surface resulted in the increases in both space charge accumulation and conductivity compared with the unaged reference. The general trends did not differ greatly when the anode and cathode contacted the oxidized surface, despite the different types of charge injection (i.e. negative and positive injection).

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