Recommendations in HV DC testing of MV cable insulation

Research and field reported data supports the theory that high voltage DC testing can reduce the life of both unaged and aged medium-voltage cross-linked polyethylene (XLPE) cable insulation. This research led an industry movement to eliminate factory DC testing, and reduce the field level and frequency of DC testing. DC factory testing identifies an imperfection in the insulation wall as well as mechanical damage. The test sequence in the factory is to perform the AC voltage withstand and corona tests first, followed by the DC withstand test. The AC withstand and corona test levels today are very demanding and locate the same insulation imperfections. Therefore, it can be inferred that today's level of AC withstand and corona testing positively locates insulation imperfections and the following DC testing is redundant and not required. Statistical analysis of factory testing shows that DC testing after AC withstand and corona tests has no additional benefit. The changes and recommendations made by the Association of Edison Illuminating Companies to DC testing are outlined.