Water tree induced breakdown in polyethylene

摘要

A breakdown mechanism based on a local enhancement of the electricnfield due to the dielectric nature of the water tree was investigated.nUsing a laboratory model made of a water needle and a facing metallicnneedle simulating a defect, it was shown that: (i) the presence of anwater tree at the water electrode clearly lowers the dielectricnstrength; (ii) the dielectric strength decreases when the water treenlength increases; and (iii) for a fixed water tree length, thendielectric strength decreases when the absorption of the light in thenwater tree increases. This last result is explained by increasing fieldnenhancement on the metallic needle due to the change in water treenpermittivity induced by the increasing water content