On-Line and Off-line PD monitoring: The Experiences in testing MV and HV apparatus from an Industrial Point of View

In recent years, an increasing demand for partial discharge (PD) testing on medium and high voltages apparatus has been observed. This includes cables, switchgear, transformers and rotating machines, both with on-line (inservice) and off-line (out-of-service) testing/monitoring practices to increase reliability and reduce financial losses due to plant downtime, unplanned outages and expensive maintenance regimes. This paper firstly presents an up-to-date overview of the online and off-line PD techniques used in the modern industries and how these techniques can be used to test for PD on the MV and HV assets. In the second part of the paper, several case studies are reported to highlight differences, advantages and disadvantages of the two different PD monitoring approaches (on-line vs offline). Finally, recommendations are made for how more effective condition monitoring (CM) of MV and HV networks can be achieved by focusing on the ‘Worst 5%’ of assets in a network based on the on-line PD testing and monitoring data.