Partial discharge measurement at DC voltage — Evaluation and characterization by NoDi∗ pattern

In this paper the requirements on PD measurement systems for DC voltage are summarized and the experience gained about the PD behavior of some typical defects in HVDC GIS and GIL are discussed. Some physical effects at different voltage levels are shown and a method for the representation and characterization of the PD pulse sequences is introduced. Special test cells with different types of defects such as a protrusion, a floating electrode, a free moving particle and a void are used for the investigations. The procedure for PD measurement at DC voltage is improved and PD pulse sequences at different gas pressures and voltage levels were recorded. In a further step the PD behavior up to the breakdown voltage was determined. The NoDi* pattern was developed for the visualization and interpretation of the measured PD pulse sequences. This pattern supports the visualization and the physical interpretation of the pulse sequences and may allow the characterization of the typical defects in HVDC GIS and GIL by a human expert.