On-line partial discharges monitoring of high voltage XLPE / fluid-filled transition joints

Partial Discharge (PD) measurement is an effective method to detect degradation processes in medium and high voltage equipment. As an example, after-laying PD test have become mandatory in many countries as a commissioning test for high voltage cable systems. This type of test can assess the presence of defects just after installation, but thermal cycling, electrical and thermal stress as well as contamination can lead to the onset of defects at a later time. To cope with defects arising during operation, the key is PD monitoring (offline tests are often too costly in terms of equipment, personnel and loss of revenues). This paper presents the application a of permanent PD monitoring system based on a Ultra-Wide band (UWB) detector to high voltage transition joints linking old fluid-filled cables with new XLPE cable lines. These cable accessories are highly critical because of the complexity of their insulation system and the fact they are realized on field (uncontrolled environment). The innovative monitoring scheme fully exploits the benefits coming from using a UWB detector, i.e., selective tracking of PD based on PD pulse characteristics. This approach enables to trend various PD sources separately, highlighting those that are associated with degradation phenomena within the insulation system. This approach will be unraveled and demonstrated by monitoring data coming from two cable lines.