Threshold voltage of luminescence and electrical tree inception in low-density polyethylene

Abstract
The characteristics of luminescence observed during the initiation of an electrical tree have been studied for polyethylene subjected to high electrical stresses. Use of a light detection system which is at least three orders-of-magnitude more sensitive than conventional partial discharge detectors shows that luminescence occurs during tree initiation and this luminescence is not due to partial discharges. Applying a constant high voltage to the polymer or interrupting the voltage several times does not change the behavior of luminescence. The light starts at about the same voltage and its intensity returns to the same value as before the interruption. This behavior is contrary to that observed for partial discharges. The luminescence inception voltage is the threshold voltage at which the polymer starts to degrade. Thus, it is important that the insulation of electrical equipment be protected from transient overvoltages which exceed the threshold level.

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