Ageing of High Voltage Cable Insulation

There is great interest in understanding the ageing and degradation of electrical insulation in an effort to improve its lifetime and efficiency. This paper investigates the affect artificial ageing by ultraviolet (UV) irradiation has on the charge movement in 100 mu m low density polyethylene (LDPE) films. Ageing takes place under a 254nm, 36W, fluorescent tube, in 3 and 7 day intervals up to a total of 17 days. Chemical changes are analyzed using Fourier transform infrared (FTIR) spectroscopy to investigate oxidation products. Samples are boiled in xylene to investigate changes in cross linking due to the UV ageing. The electrical properties are analyzed in terms of electrical strength, relative permittivity, dielectric loss and charge movement. Charge movement is investigated through space charge profiles using the pulsed electro-acoustic (PEA) technique. The emission of a faint light, known as electroluminescence (EL) is also investigated to interpret charge movement near the electrode-polymer interface. Results suggest that increases in oxidation products result in the easier conduction and recombination of charge carriers due to the carbonyl and hydroxyl groups, supported by a reduced EL emission. Space charge measurements suggest increased quantity of deep trapping sites due to slow charge decay.