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Streamer Inception from Ultra-Sharp Needles in Mineral Oil Based Nanofluids
KTH, School of Electrical Engineering and Computer Science (EECS).ORCID iD: 0000-0002-8173-8765
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.ORCID iD: 0000-0002-6375-6142
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymeric Materials.
2018 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 8, article id 2064Article in journal (Refereed) Published
Abstract [en]

Positive and negative streamer inception voltages from ultra-sharp needle tips (with tip radii below 0.5 m) are measured in TiO2, SiO2, Al2O3, ZnO and C-60 nanofluids. The experiments are performed at several concentrations of nanoparticles dispersed in mineral oil. It is found that nanoparticles influence positive and negative streamers in different ways. TiO2, SiO2 and Al2O3 nanoparticles increase the positive streamer inception voltage only, whilst ZnO and C-60 nanoparticles augment the streamer inception voltages in both polarities. Using these results, the main hypotheses explaining the improvement in the dielectric strength of the host oil due to the presence of nanoparticles are analyzed. It is found that the water adsorption hypothesis of nanoparticles is consistent with the increments in the reported positive streamer inception voltages. It is also shown that the hypothesis of nanoparticles reducing the electron velocity by hopping transport mechanisms fails to explain the results obtained for negative streamers. Finally, the hypothesis of nanoparticles attaching electrons according to their charging characteristics is found to be consistent with the results hereby presented on negative streamers.

Place, publisher, year, edition, pages
MDPI , 2018. Vol. 11, no 8, article id 2064
Keywords [en]
streamer inception, electric discharges, nanofluids, mineral oil
National Category
Other Chemistry Topics
Identifiers
URN: urn:nbn:se:kth:diva-238926DOI: 10.3390/en11082064ISI: 000446604100143Scopus ID: 2-s2.0-85052822998OAI: oai:DiVA.org:kth-238926DiVA, id: diva2:1263051
Note

QC 20181114

Available from: 2018-11-14 Created: 2018-11-14 Last updated: 2019-08-01Bibliographically approved
In thesis
1. Pre-breakdown Phenomena in Mineral Oil Based Nanofluids
Open this publication in new window or tab >>Pre-breakdown Phenomena in Mineral Oil Based Nanofluids
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mineral oil is a dielectric liquid commonly used in high voltage equipment such as power transformers. Interestingly, it has been experimentally observed that the dielectric strength of the mineral oil is improved when nanoparticles are added. However, the mechanisms behind these improvements are not well understood, hindering the further innovation process of these so-called nanofluids. This thesis aims to contribute to the understanding of the mechanisms explaining the dielectric strength improvement of the base oil when nanoparticles are added.For this, several experiments and numerical simulations are performed in this thesis. The initiation voltage of electric discharges infive different kind of nanofluids was measured. The large data set obtained allowed to cast experimental evidence on the existing hypotheses that are used to explain the effect of nanoparticles. It is found that hydrophilic nanoparticles hinder the electric discharge initiation from anode electrodes. On the other hand, electric discharge initiation from cathode electrodes was hindered by nanoparticles with low charge relaxation time.The electric currents in mineral oil and nanofluids were also measured under intense electric fields (up to 2GV/m). It is found that the addition of certain nanoparticles increases the measured currents. The possible physical mechanisms explaining the measured currents inmineral oil with and without nanoparticles were thoroughly discussed based on results of numerical simulations. Preliminary parameters used in this thesis to model these mechanisms led to a good agreement between the measured and simulated electric currents.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. p. 69
Series
TRITA-EECS-AVL ; 2019:58
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-255605 (URN)978-91-7873-241-8 (ISBN)
Public defence
2019-09-06, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20190802

Available from: 2019-08-02 Created: 2019-08-01 Last updated: 2019-08-02Bibliographically approved

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Aljure, MauricioBecerra Garcia, MarleyKarlsson, Mattias E.

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