Influence of fibrous contaminants on dielectric property of XLPE insulation

The influence of fibrous contaminants on the electrical breakdown strength of crosslinked polyethylene (XLPE) insulated cables and the breakdown mechanism resulting from fibrous contaminants are discussed. It has been found that natural cotton fibers decrease the dielectric strength of the XLPE insulation much more than synthetic fibers, which means that cotton fabrics should not be allowed into the jointing room, especially during the metal mold setting. Microscopic observation showed that the influence was related to the microstructure of the fiber. The microcavity which exists in cotton fiber might play an important role under the electric field. Another approach to studying the breakdown mechanism showed that the breakdown by the fiber was preceded by a partial discharge which corresponded to the treeing from the tip of the fiber