Damage to Power Cable from a Neutral Wire Repair


Posted in: Workmanship, Wind


IMCORP's Factory Grade® assessment indicated a PD site in an underground medium voltage power cable at a wind farm in Texas. Initial inspection of the PD site did not show any evidence of an issue. IMCORP's confidence in our assessment prompted a more thorough analysis of the cable. A 60-foot section was sent to the cable's manufacturer to conduct further testing to verify IMCORP's claims. The manufacturer performed a simple DC HiPot to force the cable to failure.  Once the cable failed, the manufacturer removed the jacket and found a compromised section in the semi-con. Upon this discovery, they referenced the relevant manufacturing records for the cable. Neutral wires had broken during the cable's fabrication; to repair this, it had been necessary to cut through the cable's jacket. Inadvertently, the semi-con had also been cut during this process. This was not detected before the cable shipped because the QC partial discharge test was never repeated after the repair; so, the cable shipped defective.

The rectangular section draws attention to the point of the cut in the semi-con; the dashed line draws attention to the cut itself. It should be noted that IMCORP's Factory Grade® assessment detected PD activity before the fault in the semi-con material had occurred, as that was a result of subsequent DC HiPot testing.