HVDC GIS/GIL - PD Identifcation by NoDi* Pattern

The partial discharge measurement is one of the most meaningful tools for the assessment of all types of high voltage components. For AC voltage the measurement setup, the measurement procedure and especially the representation and interpretation of the results is defined in the standard. These cannot fully adapt for DC voltage. For the reason that the physics of the PD behaviour of some defects are partly different new requirements on PD measurement systems and the methods for interpretation are essential. In this paper the experience about the PD behaviour of some typical defects of GIS and GIL at DC voltage are discussed. Also the physical effects at different voltage levels are summarised. Special test cells with different types of protrusions, a floating electrode and three types of bouncing metallic particles are used for these investigations. A huge number of PD pulse sequences at variable gas pressures and different voltages is recorded and the influence of the geometrical parameters are investigated. In another step the PD behaviour close to the breakdown voltage was determined to assess the criticality of some defects. To visualize the measured PD pulse sequences the NoDi* pattern is used and further developed. The advantage of this pattern is the possibility to characterize the typical defects in HVDC GIS and GIL by a human expert.