Electrical Treeing in Fluoropolymer Cable Insulation

This paper examines the electrical treeing phenomenon in fluoropolymers under AC voltage. A specialised test setup was designed to evaluate two distinct fluoropolymers, fluorinated ethylene propylene (FEP) and perfluoroalkoxy alkane (PFA), with cross-linked polyethylene (XLPE) serving as the reference material, given its well-documented AC treeing characteristics. Tree growth in both fluoropolymers were found to follow a somewhat classical three-stage pattern, developing bush-like trees with insulating channels. In XLPE at the same growth voltage the trees were bush-branched with a higher propagation rate than in FEP and PFA. The lower propagation rate in fluoropolymers is likely related to the higher bond strength of the carbon-fluorine bonds compared to the carbon-hydrogen bonds in XLPE. Breakdown in the materials produced indications of carbonisation products in the breakdown channel.