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Second Mode Positive Streamers Propagating Along Mineral-oil/solid Interfaces
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.ORCID iD: 0000-0002-4800-9990
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.ORCID iD: 0000-0002-6375-6142
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.ORCID iD: 0000-0002-1924-6954
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0001-8622-0386
(English)Manuscript (preprint) (Other academic)
Abstract [en]

This paper presents an experimental study on second mode positive streamers propagating along mineral-oil/solid interfaces. The inception and propagation of these streamers is investigated with different impregnated solids (low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) polyvinylidene fluoride (PVDF), two papers referred to as kraft paper and a kraft fibril paper, made from cellulosic micro and nano fibrils, a lignin-free paper and a paper with high lignin content referred to as k107 kraft paper). Streamers are initiated in a point-plane configuration under step voltages with 35 ns rise time. The radius of the tip is 2.9 μm and the solid is installed in an inclined position in close contact to the point electrode. Shadowgraphs, charge and light recording of the streamers are reported for each case. Furthermore, estimations of the streamer stopping length, velocity, current and average charge are reported. It is found that the streamer inception is influenced by the solid interface indicating that the inception process is not only conditioned by the field at the tip but also by the interface. A time delay is observed before the initiation of the streamer and probably correlated with the initiation process and formation of the gaseous phase. Additionally, the threshold propagation voltage of the second mode streamers at mineral-oil/solid interfaces is shown to be independent of the interface. It is also shown that the different characteristics of streamers propagating along the tested interfaces cannot be fully explained by the capacitive coupling effect due to permittivity mismatch. Thus, it is suggested that the characteristics of streamers propagating near interfaces is affected by other properties of the solid such as chemical composition, wettability and surface roughness.

National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-213423OAI: oai:DiVA.org:kth-213423DiVA, id: diva2:1137251
Note

QC 20170901

Available from: 2017-08-30 Created: 2017-08-30 Last updated: 2017-09-01Bibliographically approved
In thesis
1. On the inception and propagation of streamers along mineral-oil/solid interfaces
Open this publication in new window or tab >>On the inception and propagation of streamers along mineral-oil/solid interfaces
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents an experimental study of positive and negativestreamers propagating along mineral-oil/solid interfaces under square highvoltage pulses. The thesis includes the design and construction of anexperimental setup to studying the streamers in a point-plane configurationcapable to detect streamer parameters such as velocity, length, propagationtime, emitted light and charge.The first part of this experimental study is devoted to the analysis of thestreamer inception at mineral-oil/solid interfaces under negative polarity. Thestreamer inception voltage and charge recordings are reported for eachmineral-oil/solid interface. It is found that only solids with a permittivitysimilar to that of mineral oil can influence the streamer inception voltage.Solids with matched permittivity such as LDPE and PTFE increase the inceptionvoltage. The cases with solids with higher permittivity than mineral oil havesimilar inception voltage as the streamer incepted in the liquid bulk withoutsolid. The second part is devoted to studying the propagation of first mode negativestreamers along different mineral-oil/solid interfaces. A comparison of theelectrical and physical properties of the streamers (e.g. charge, length,velocity, etc.) is presented. Solid samples with different chemical compositionand different physical properties are used. The solid samples are anoil-impregnated kraft paper and an low-porosity paper referred to as kraftfibril paper made from cellulosic micro and nano fibrils. Polymeric films madeof low density polyethylene (LDPE), polyethylene terephthalate (PET),polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) are also usedas the solid. Streamers propagating along the liquid/solid interface arecompared with streamers developing in mineral oil without solid. Streamerspropagate longer and faster along solids with low surface roughness, lowporosity and higher electrical permittivity than mineral oil showing aquasi-continuous injection of charge in the early stage of propagation.The third part of the experimental study deals with second mode positivestreamers propagating along mineral-oil/solid interfaces. The inception andpropagation of the streamer are investigated using different mineral-oil/solidinterfaces. Measurements of the streamer velocity, charge, stopping length,propagation time, together with light recordings and shadowgraphs are reported.It is found that the interface can influence the streamer inception voltage,branching, stopping length, velocity, charge and current. Properties of thesolid and of the interface (i.e. surface roughness, permittivity, wettability)are parameters that influence the streamer propagation.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. p. 74
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-213426 (URN)978-91-7729-397-2 (ISBN)
Public defence
2017-09-15, V2, Teknikringen 76, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20170901

Available from: 2017-09-01 Created: 2017-08-30 Last updated: 2017-09-04Bibliographically approved

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