Critical issues in the PD testing methodology for XLPE-insulated MV cables: an experimental case

This paper describes some critical issues arising during the partial discharge (PD) testing of a 500m delivery length of an XLPE-insulated MV cable. At first, conventional PD measurements were performed on the whole length by using a standard acquisition system; PDs activity was detected, but the system allowed the operator to localize the PDs only on a length of 70 m. A visual inspection of this section highlighted the presence of an excoriation in the outer sheet. Aiming at a more accurate pin-pointing of the defect, more measurements were carried out in the proximity of the outer defect using a portable PD detection system. These measurements showed PDs activity, whose source was located and identified as consisting in internal defects on the inner semicon in proximity of the external excoriation. This proves how PD detection portable instruments are able, in cases like this, to locate the PD source and provide indications for its correct classification.