While at a renewable energy generation facility, IMCORP was conducting a Factory Grade® assessment on collector system cables when this pair of defects was uncovered. The defects were located less than 150 feet apart and appeared to be in cable insulation (very rare in new cable).
Following IMCORP’s recommendations, the site owner had just over 200 feet from the mid-span of the cable removed. The section was replaced with new cable and a pair of splices. The new complete cable system was reassessed and passed all pertinent manufacturers’ standards for partial discharge activity.
The defective section was sent to IMCORP for a comprehensive laboratory analysis. This analysis found a modest amount of ambers in the cable insulation. An amber is essentially overheated TRXLPE material that gets embedded in the insulation during the extrusion process (a cross section of an amber can be seen in the image above). Ambers are not usually a significant problem, but in two specific locations on this cable, they had delaminated from the surrounding insulation. The delamination introduced voids, and those voids were the source of the sub-standard partial discharge activity. This was a serious defect in that the void spanned over twenty-five percent of the cable insulation.