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Corona behavior of HVDC overhead lines plays a significant role when dimensioning transmission lines. Rain constitutes an important study case since corona effects (e.g. losses, discharge amplitudes) are considerably affected. In this paper, imaging methods are introduced to investigate the impact of rain on corona behavior. Geometrical properties of rain drops on a stranded conductor were extracted. UV-images were used to precisely locate discharges. The methods' capabilities are demonstrated using data from an indoor test line during a simulated rain shower. Optical and electrical data were correlated. These methods aim to support the development of surfaces with favorable corona properties.

It is known that electrified droplets deform and may become unstable when the electric field they are exposed to reaches a certain critical value. These instabilities are accompanied by electric discharges due to the local enhancement of the electric field caused by the deformed droplets.Here we report and highlight an interesting aspect of the behavior of unstable water droplets and discharge generation: by implementing wettability engineering, we can manipulate these discharges. We demonstrate that wettability strongly influences the shape of a droplet that is exposed to an electric field. The difference in shape is directly related to differences in the critical value of the applied electric field at which inception of discharge occurs. Using theoretical models, we can predict and sufficiently support our observations. Thus, by tailoring the wettability of the surface, we can control droplet's behavior from expediting the discharge inception to completely restricting it.

a b s t r a c tCorona behavior of HVDC overhead lines plays a significant role when dimensioning transmission lines. Rain constitutes an important study case since corona effects (e.g. losses, discharge amplitudes) are considerably affected. In this paper, imaging methods are introduced to investigate the impact of rain on corona behavior. Geometrical properties of rain drops on a stranded conductor were extracted. UVimages were used to precisely locate discharges. The methods' capabilities are demonstrated using data from an indoor test line during a simulated rain shower. Optical and electrical data were correlated. These methods aim to support the development of surfaces with favorable corona properties.

This paper presents the results of a series of indoor laboratory experiments carried out on DC energized overhead conductors subjected to simulated rainfall. In a first set of experiments, the impact of rain intensity on the corona onset voltage and total corona losses was investigated. With regard to the onset voltage, no significant impact was observed, whereas a weak positive correlation with total corona losses could be established. In a second set of experiments, the impact of different conductor types on the same two quantities was examined. The most notable result is that the combined use of Z-profiled-strands and sand-blasted surfaces lead to reductions in the total corona current of around 29% and 42%, for positive and negative polarity respectively. The corresponding reduction of ground level ion currents and ion coupling with parallel conductors is expected to be of the same order of magnitude.

This publication presents the results of a series of laboratory investigations on the DC ion current coupling between nearby AC and DC conductors, which is an important consideration in the design of hybrid AC/DC transmission towers. The corona activity depends on the surface condition of the conductor. Whether or not the conductors produced corona was controlled by selectively wetting them. This allowed a distinction of the observed effects into field interactions and space charge interactions. One key result is that the presence of an AC field alone does not have any effect on the DC ion current coupling. Corona activity on the AC conductor, however, may significantly increase DC ion current components in both conductors. Another important finding is that the DC current in the AC conductor for the case of corona activity on both conductors was significantly larger than the sum of the DC currents based on corona activity on either conductor individually. This indicates that the bipolar space charge environment between a coronating AC and DC line plays an important role in the ion current coupling.

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