In this contribution, the partial discharge behavior of two types of floating electrodes under DC stress in air at atmospheric pressure are investigated. Either a hexagonal-shaped nut or a sphere are positioned at a distance of 0.4 mm to the high voltage electrode. The influence of the geometry of the floating electrodes as well as the level and polarity of the applied DC voltage on the partial discharge activity are investigated. Several PD measurement techniques are used simultaneously, namely electrical measurement, ultra-high frequency (UHF) and both high frequency current transformer (HFCT) and shunt measurements. The obtained data is post-processed and visualized with Pulse Sequence Analysis (PSA) diagrams in order to provide characteristic patterns of the investigated defect. In addition, a corona camera detecting the light emissions generated by the discharges provide a further understanding of the defect mechanisms.@en

Partial Discharges (PD) have long been studied under AC field stress and are widely accepted as a good indicator of component health. However, the advent of HVDC brought new challenges, as the pre-existing knowledge in the area of PD is not applicable to DC. The discharge behavior has been found to be erratic and there is no plausible evidence yet, that correlates discharges with insulation deterioration. The inability to produce stable behavioral patterns in DC-PD has also led to a spark in interest in the application of several non-conventional measuring methods, e.g. the measurement using UHF sensors. Therefore, this paper deals with the measurement of time synchronized PD measurements through conventional electrical and UHF methods for a novel comparison of DC discharge patterns generated by a needle-plate electrode arrangement in air. The different configurations of the defect are studied under both voltage polarities and the observations are discussed in terms of pulse magnitude and repetition rate. In addition, this paper exploits the opportunities of computational power for post-processing to obtain Pulse Sequence Analysis (PSA) diagrams of the discharge data.@en