Characteristics of partial discharge under high voltage AC & DC conditions

High voltage AC has been the technology of choice for electricity transmission since the creation of electric grids throughout the world. However due to a wide range of factors, including the availability of new AC-DC and DC-AC converter designs, an increasing requirement for subsea interconnections for off-shore wind and continental super-grids, a greater emphasis on efficient operation for cost and environmental reasons, and a desire for ever-increasing transmission distances, high voltage DC is increasingly seen as an attractive and viable choice. While HVDC technologies have existed for as long as HVAC, their lack of significant use until recently mean that several gaps in knowledge exist, including in the area of condition monitoring of assets. One such condition monitoring technology is partial discharge monitoring, which, while it is a mature technology that is frequently used in AC systems, it has had limited deployment under DC conditions. As such it still lacks the field experience, well-developed standards, technical expertise, and overall knowledge base for DC that exists for AC. This thesis presents research into the characteristics of partial discharge under both AC and DC conditions. A review of relevant literature is presented, followed by the research methodology, including the use of thin film polymer samples, and a 'coring' method for introducing an artificial void into a cable sample. Data and analysis are then presented which compare the presentation of PD in different materials, the impact of multiple void configurations on PD, and statistical analysis of the PD pulses themselves. These analyses demonstrate clear differences between the behaviour of PD, and the characteristics of the PD pulses themselves, under the different voltage types, void configurations, and materials investigated, with potential reasons for these differences discussed, and suggestions made for how knowledge of these differences should affect the detection of PD, and, therefore improve condition monitoring of both AC and DC equipment.High voltage AC has been the technology of choice for electricity transmission since the creation of electric grids throughout the world. However due to a wide range of factors, including the availability of new AC-DC and DC-AC converter designs, an increasing requirement for subsea interconnections for off-shore wind and continental super-grids, a greater emphasis on efficient operation for cost and environmental reasons, and a desire for ever-increasing transmission distances, high voltage DC is increasingly seen as an attractive and viable choice. While HVDC technologies have existed for as long as HVAC, their lack of significant use until recently mean that several gaps in knowledge exist, including in the area of condition monitoring of assets. One such condition monitoring technology is partial discharge monitoring, which, while it is a mature technology that is frequently used in AC systems, it has had limited deployment under DC conditions. As such it still lacks the field experience, well-developed standards, technical expertise, and overall knowledge base for DC that exists for AC. This thesis presents research into the characteristics of partial discharge under both AC and DC conditions. A review of relevant literature is presented, followed by the research methodology, including the use of thin film polymer samples, and a 'coring' method for introducing an artificial void into a cable sample. Data and analysis are then presented which compare the presentation of PD in different materials, the impact of multiple void configurations on PD, and statistical analysis of the PD pulses themselves. These analyses demonstrate clear differences between the behaviour of PD, and the characteristics of the PD pulses themselves, under the different voltage types, void configurations, and materials investigated, with potential reasons for these differences discussed, and suggestions made for how knowledge of these differences should affect the detection of PD, and, therefore improve condition monitoring of both AC and DC equipment