Test procedure and acceptance criteria for PD commissioning testing of transmission class cables

Over the last decade, partial discharge testing has gained acceptance as a valid diagnostic tool for condition assessment of cable insulation. It is well known and understood that the results obtained from a partial discharge test depend not only on the conditions under which the test was performed but also on the test equipment itself including the type of sensor used and its location. The issues related to actual discharge, induced charge and measured apparent charge are also well understood. Yet, for commissioning testing of solid dielectric, test specifications often reference magnitude levels in pC of apparent charge as the only pass/fail acceptance criterion. The practice is based on factory acceptance testing of individual cable components. This paper outlines the difference between PD testing performed on individual components in the factory and PD testing performed on installed systems in the field with respect to magnitude calibration of PD pulses. The paper further proposes a test procedure as well as a framework for acceptance criteria for after-laying PD commissioning testing of transmission class cable and provides test experience gained through 5 years of testing of HV and EHV cable systems.