Partial discharge in medium voltage three-phase cables

Cable distribution networks are inherently complex and inaccessible systems; many of them are coming to the end of their original design life. As assets, they represent a dynamic and challenging issue with regard to the tasks of maintenance and management. Partial discharge (PD) has long been recognized as both a cause and symptom of the degradation of dielectric materials that protect high voltage plant. Utilities use the analysis of PD activity to make pre-fault decisions in areas such as maintenance, supply continuity and asset management. On-line PD monitoring systems are still in their relative infancy. An EDF Energy Networks funded research is investigating and identifying trends in PD activity associated with specific faults that commonly occur in distribution networks. In this paper an experiment to mimic the conditions experienced by on-line cable sections in the field is described. PD measurement has been obtained using conventional techniques covered in IEC 60270 in parallel with a commercially available substation monitor that is employed in distribution networks worldwide. Later work will involve using this experiment to PD test cable samples that contain a range of defects. It is hoped that each defect mechanism will produce an unique trend in PD activity as it degrades towards failure.