On-line partial discharge monitoring system for distribution networks

Partial discharges (PD) occur as a result of dielectric breakdown in electrical insulation under high voltage stress. PD activity, once initiated, causes chemical and physical degradation of insulating material and can lead to catastrophic failure. Early warning of PD activity and localisation is considered essential to ensure the reliable operation over the long term of high voltage equipment including cables, cable accessories and switchgear. PD detection in high voltage cable and cable accessories is usually carried out with test objects offline, requiring potentially significant interruption of service. An online detection system is preferable but difficult to calibrate apparent charge magnitudes due to changes in real distribution network loading and topologies. An online PD detection system with continuous calibration has been developed to determine the apparent charge magnitudes of PD activity and locations in a section of in-service distribution network with high monitoring frequency and no requirement to take cables off line. Results of the on-line PD monitoring system in a typical urban distribution network in Spain are presented. System components including the online calibration pulse injector, capacitive sensors for high frequency PD pulse detection, and data acquisition, processing and communication components at each monitoring site are presented.