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On the inception and propagation of streamers along mineral-oil/solid interfaces
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.ORCID iD: 0000-0002-4800-9990
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: urn:nbn:se:kth:diva-213426ISBN: 978-91-7729-397-2 (print)OAI: oai:DiVA.org:kth-213426DiVA, id: diva2:1137267
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
List of papers
1. Inception of first mode negative streamers at liquid/solid interfaces
Open this publication in new window or tab >>Inception of first mode negative streamers at liquid/solid interfaces
(English)In: Journal of Physics D: Applied PhysicsArticle in journal, Editorial material (Refereed) Submitted
Abstract [en]

This paper presents an experimental study on the inception of first mode negative streamers at different mineral-oil/solid interfaces. This study is performed with a point-plane configuration immersed in mineral oil (point cathode). The mineral-oil/solid interface is done by assembling a solid in an inclined position into the point-plane gap. The solid is in contact (or in the proximity) with the point electrode tip. The tested solids are a kraft paper, a paper made from cellulosic micro and nano fibrils and different polymeric films (low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF)). These solids have different relative permittivity and structural composition. It is found that the streamer inception voltage is statistically similar for the cases with solids with higher permittivity than mineral oil. The streamer inception voltage for the case without any solid barrier is also statistically similar to the cases with solids with higher permittivity than mineral oil. It is also found that the inception voltage is higher for streamers initiated at permittivity-matched interfaces (cases with LDPE and PTFE). Additionally, the influence of the spatial limitation with the solid surface to the volume where the streamer initiation process takes is performed with PTFE by varying the distance between the point electrode and the solid surface. It is shown that the streamer inception voltage depends on the distance between the point electrode and the solid surface. Furthermore, It is observed that the streamer inception voltage is also influenced when the distance between the point electrode and the surface of the PTFE is several micrometers (twenty times longer than the penetration depth of the avalanche responsible of streamer initiation). Additionally, it is also shown that a recently-proposed streamer inception criterion is unsuitable to predict the streamer inception conditions close to permittivity matched and mismatched liquid/solid interfaces.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-213421 (URN)
Note

QC 20170901

Available from: 2017-08-30 Created: 2017-08-30 Last updated: 2017-09-01Bibliographically approved
2. First Mode Negative Streamers along Mineral Oil-solid Interfaces
Open this publication in new window or tab >>First Mode Negative Streamers along Mineral Oil-solid Interfaces
Show others...
2017 (English)In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 24, no 4Article in journal (Refereed) Published
Abstract [en]

This document presents an experimental study on the propagation of first mode negative streamers along mineral oil-solid interfaces. Samples made of an oil impregnated kraft paper and a low-porosity paper made from cellulosic micro and nano fibrils, as well as different polymeric films (low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF)) are used as the solid. A comparison of the length, charge and velocity of streamers for all different mineral oil-solid interfaces is reported. It is shown that streamers propagate longer and faster along mineral oil-solid interfaces with low surface roughness, low porosity and higher electrical permittivity than mineral oil. Those streamers show a quasi-continuous injection of charge in the early stage of their propagation. This quasi-continuous charge injection consists of a sequence of small charge steps separated by few tens of nanoseconds in between. In comparison, the streamers that propagate along surfaces with similar permittivity to the mineral oil have lower injection of charge and higher stopping voltage conditions than streamers propagating free in the liquid without any solid barrier.

Place, publisher, year, edition, pages
IEEE, 2017
National Category
Engineering and Technology
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-213422 (URN)10.1109/TDEI.2017.006545 (DOI)000411003700050 ()2-s2.0-85029818465 (Scopus ID)
Note

QC 20170901

Available from: 2017-08-30 Created: 2017-08-30 Last updated: 2017-10-12Bibliographically approved
3. Second Mode Positive Streamers Propagating Along Mineral-oil/solid Interfaces
Open this publication in new window or tab >>Second Mode Positive Streamers Propagating Along Mineral-oil/solid Interfaces
(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:nbn:se:kth:diva-213423 (URN)
Note

QC 20170901

Available from: 2017-08-30 Created: 2017-08-30 Last updated: 2017-09-01Bibliographically approved
4. Influence of Paper Properties on Streamers Creepingin Mineral Oil
Open this publication in new window or tab >>Influence of Paper Properties on Streamers Creepingin Mineral Oil
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2017 (English)In: Proceedings of IEEE International Conference on Dielectric Liquids, ISSN 2153-3725, E-ISSN 2153-3733Article in journal (Refereed) Published
Abstract [en]

This work presents an experimental study ofsecond mode positive streamers propagating along mineral oilpaperinterfaces. A point-plane arrangement immersed inmineral oil with the paper inclined 60 degrees to the planeelectrode is used to create the liquid-solid interface. Kraft paperand a kraft fibril paper, made from cellulosic micro and nanofibrils, with higher density and lower surface roughness are usedas the solid materials. High speed shadowgraphy and chargerecordings are used to compare the propagation of second modepositive streamers along the mineral oil-kraft paper and mineraloil-kraft fibril paper. Streamers creeping along the mineral oilkraftpaper interface propagate mainly into the liquid, with oneor two main filaments. In comparison, the streamers propagatingalong the kraft fibril paper show a strong reduction of thebranching; these streamers consist of a single filament thatpropagates exactly on the solid surface. Streamers along the kraftfibril paper also have longer propagation time than for the casewith kraft paper. Mutual electrostatic shielding betweenfilaments is observed for the streamers creeping on the kraftpaper. An electrostatic analysis of the influence of permittivity,density and surface roughness of the solid in the electricalproperties of the streamer filaments is also performed.

Place, publisher, year, edition, pages
IEEE, 2017
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-213424 (URN)
Conference
19th International Conference On Dielectric Liquids ICDL 2017
Note

QC 20170901

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

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