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The spectra of light emitted during electrical-tree initiation in low-density polyethylene used in high-voltage cables were investigated. Light in the visible and in the near-ultraviolet range was detected. Low-density polyethylene subjected to highly divergent fields at voltages below the light-inception level did not develop an electrical tree, and it is suggested that the light-inception voltage is the threshold for insulation degradation. The ultraviolet light emitted at voltages above the light-inception level could cause degradation of the polymer. A model is proposed to explain the mechanism of electroluminescence. Ultraviolet stabilizers added to the polymer prolonged the time to electrical-tree initiation by preventing photodegradation of the polymer.

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The boundary element method is used to calculate the electric field profiles at needle tips commonly used for electrical treeing tests. Field distributions are also obtained for polyethylene containing a space charge, at the needle tip, and are compared with the values previously obtained by the finite difference method.