Light and tree inception characteristics of XLPE at elevated temperatures

The authors describe the characteristics of light emission at an XLPE a (cross-linked polyethylene)-semicon interface held above and below the temperature at which the crystallites of the polymer start to melt. The spectra of EL (electroluminescence) and the light inception voltage of degassed, an N₂- and SF₆-impregnated XLPE are reported. It is shown that XLPE subjected to elevated temperature emits luminescence even without voltage application. This light is attributed to TL (thermoluminescence) which depends on the concentration of the crosslinking by-products present in the polymer. The TL spectra are only in the visible range. On the other hand, the XLPE-semicon interface held above room temperature and subjected to high electric stress emits EL, and the spectra of this light are in the visible and the UV ranges. Although the intensity of EL emitted at high temperature is lower than that emitted at room temperature, the UV light can photodegrade the polymeric insulation, which can lead to electrical tree inception