Electrical ageing effects in polyethylene

It is known that the electric strength of polyethylene decreases with the age of the material. However, it is apparent that the voltage-life curves for polymer insulation are more complex than the traditional Power Law suggests. In practice, a plot of log_eE versus log_et may show marked changes in slope, implying various mechanisms of failure depending on the stress level. Hence, a linear extrapolation from test results at high stress is a poor guide to life at working stress. This paper reports on an on-going investigation into the existence of other possible causes of insulation degradation, i.e. mechanisms which would, under normal high stress test methods, be masked by the more active causes of insulation deterioration. To build up a matrix of information on ageing and possible failure mechanisms of PE, all work to date has used additive free HDPE (Rigidex 006-60). HDPE was chosen because of the relative simplicity of its molecular structure and has been well characterised. The effects of additives may be subsequently examined along with LDPE and XLPE