Comparison between the electroluminescence and space charge of ultraviolet and thermally aged low density polyethylene

Understanding the long term electrical degradation of polymeric insulation is of great importance in extending the life of high voltage cable insulation. Space charge is thought to play a significant role and the behaviour and energy dissipations of charge carriers within polymeric materials are of continued interest. Electroluminescence (EL) is an alternative method of investigating the charge at the electrode-polymer interface. EL is thought to occur due to the energy release from injection, trapping and recombination of charge carriers at the sample surface, the changes in the material trapping properties due to ageing will have an effect on this. This paper compares changes between 100μm virgin and aged samples of low-density polyethylene (LDPE), ageing taking place in an oven at an elevated temperature of 313K under an ultraviolet fluorescent tube. Changes due to oxidation are shown from Fourier Transform infrared (FTIR) spectroscopy. Space charge results are collected using the pulsed electroacoustic (PEA) method and point on wave EL results using uniform parallel electrodes and detected with a highly sensitive electron multiplying charge coupled device (EMCCD) camera. Results show a change in both intensity and phase angle of point on wave EL measurements with sample ageing. Space charge measurements suggest a reduction in the bulk trapping sites but with an increase near the electrodes.