2 results
Search Results
Now showing 1 - 2 of 2
- ItemPositive streamers: inception and propagation along mineral-oil/solid interfaces(Bristol ; Philadelphia, PA : IOP Publishing Ltd., 2020) Ariza, David; Hollertz, Rebecca; Methling, Ralf; Gortschakow, SergeyThis paper presents an experimental characterization of the prebreakdown phenomena in liquid/solid interfaces. The characterization is devoted to the 2nd mode positive streamers initiated and propagated along interfaces of mineral-oil and solids with different chemical composition and physical properties. Polymers of low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) polyvinylidene fluoride (PVDF) and papers made of kraft paper and a kraft fibril paper (made from cellulosic micro and nano fibrils), lignin-free paper and paper with high lignin content (referred to as k107 kraft paper) are used as the solid to study their influence on the streamer inception and propagation. The streamers are initiated at the interface by applying steps of voltage to a point-plane electrode arrangement with a solid (dielectric barrier) into the gap. The solid is placed diagonal to the oil gap and near to the point electrode. Shadowgraphs, charge and light intensity recordings are obtained during the inception and propagation of the streamers. Thus, estimations of the streamer length, velocity, current and average charge, are also presented. A time delay has been observed before the initiation of the streamer. This delay is probably correlated to the initiation process and formation of the gaseous phase of the streamer near to the interface. The threshold propagation voltage of the 2nd mode streamers at mineral-oil/solid interfaces is shown to be independent of the interface. However, the inception voltage is highly influenced by the interface. Additionally, the observed characteristics of streamers propagation (e.g. current, length, velocity, etc) along the tested interfaces cannot be fully explained by a capacitive coupling effect (permittivity mismatch). This open a discussion for the possibility that properties of the solid such as chemical composition, wettability and surface roughness can influence the streamer propagation.
- ItemFirst‐mode of negative streamers: Inception at liquid/solid interfaces(Hoboken, NJ : Wiley, 2021) Ariza, David; Beroual, Abderrahmane; Methling, Ralf; Gortschakow, Sergey; Chamorro, Harold R.An experimental study of the inception of the first-mode negative streamer at liquid/solid interfaces is presented in this article. The study is performed with a point-plane configuration under square high voltage pulses. The electrode configuration is immersed in mineral oil and the liquid/solid interface is assembled in contact with the point electrode or in its vicinity. Four polymers and two impregnated papers have been tested as solids of the liquid/solid interface. Thus, it is possible to compare the influence of different parameter of the solid and the interface on the streamer inception. For example: Permittivity, solid surface roughness, chemical composition, etc. It has been observed that streamer inception voltages at interfaces with solids of higher permittivity to that of the mineral oil are statistically similar. Additionally, streamer inception voltages of streamer initiated free in the oil (no liquid/solid interface) are similar to that of the inception voltage of cases with solids with high permittivity. In contrast, the inception voltage of streamers initiated at permittivity matched interfaces are shown to be highest of the cases. The streamer inception voltage is also studied for different distances between the liquid/solid interface and the point electrode with a permittivity matched interface. The results show a dependency of the inception voltage and the distance between the point electrode and the interface. Finally, an analysis of the observation is performed to show that the Townsend-Meek criterion cannot predict the obtained results.