Electroluminescence measurements in polyethylene insulation

Polymers used as electrical insulation in high voltage underground power cables have excellent short term mechanical and dielectric properties. They can however be susceptible to long term deterioration due to the application of high electrical stress. There is a need to further understand the process of electrical ageing, which implies detecting and characterising the degradation. Detection is however often achieved once ageing is already significant, for example when partial discharge activity is present from a large enough microcavity. A method for early detection of electrical ageing is therefore necessary and electroluminescence (EL) is known to be such a method. This paper places emphasis on the description of a new experimental arrangement used to detect this very low level of light and to determine the spectral and spatial resolution of EL. It presents the characteristics of EL emitted in low density polyethylene (LDPE) and crosslinked polyethylene (XLPE) thin plaques in a uniform field configuration at room temperature under ac stress.