FIELD CASE STUDY OF MEDIUM-VOLTAGE CABLE ACCESSORIES WITH PARTIAL DISCHARGES IN THE HYDRO-QUEBEC UNDERGROUND DISTRIBUTION NETWORK

Most of the power failures in Hydro-Quebec’s underground distribution network occur at cable joints. Some are due to partial discharges inside these joints and the corresponding degradation of their electrical insulation. The network consists mainly of XLPE cable with EPDM rubber premolded accessories. Since 2004, Hydro-Quebec has been using its new on-line portable partial-discharge analyzer (PDA) for the detection, location and interpretation of PDs in its distribution network [1]. The analyzer is used both to ensure safety and to perform predictive maintenance by removing defective accessories before they fail. The scope of this study is to establish the relationship between the diagnosis based on PD measurements in the field and the seriousness of defects in cable accessories. To do this, many cable joints plagued with partial discharges and dielectric hotspots were withdrawn from the field for testing and analysis in our laboratory. Correlations with Hydro-Quebec’s infrared diagnosis [1-2] for cable joints will also be made. Finally, we will try to estimate the remaining field life of cable joints with defects.