Contamination Detector For Extrudable Dielectrics

The reliability of extruded dielectric cables depends, to a large extent, on the absence of impurities in the insulation. Electrical and electrochemical treeing are, in part, caused by the presence of contaminants. This report describes a new system capable of inspecting and rejecting individual, contaminated polvethvlene pellets prior to their entry into cable insulation extruders. The system consists of an electro-optical sorting device that views a moving stream of pellets and detects small changes in light reflection caused by the darker contaminants. Upon detecting the presence of a contaminant, that section of the pellet stream is removed from production. Laboratory and plant test results are reported. Data concerning: (a) equipment capability, and (b) contaminants removed during production, are discussed. The work reported has been sponsored by the Electrical Power Research Institute (RP7865).