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On the injection and generation of charge carriers in mineral oil under high electric fields
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. ABB Corp Res, Vasteras, Sweden..ORCID iD: 0000-0002-6375-6142
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
2019 (English)In: JOURNAL OF PHYSICS COMMUNICATIONS, ISSN 2399-6528, Vol. 3, no 3, article id UNSP 035019Article in journal (Refereed) Published
Abstract [en]

Charge injection and generation mechanisms under intense electric fields (up to 10(9)Vm(-1)) in mineral oil are assessed experimentally and numerically. For this, current-voltage characteristics under positive and negative polarities are measured in a needle-plane configuration using sharp needles (with tip radius R-tip <= 1.1 mu m). In addition, a state of the art electro-hydrodynamic (EHD) model is implemented to calculate the contribution of the different mechanisms on the high-field conduction currents in the liquid. In order to evaluate exclusively the contribution of field emission, experiments are also performed in vacuum. It is found that neither field emission nor field ionisation can explain the conduction currents measured in mineral oil. It is proposed that field molecular ionisation, as described by Zener tunnelling model for solids, and electron impact ionisation are the processes dominating the generation of excess electron-ion pairs in mineral oil under positive and negative polarity, respectively. It is also shown that Zener molecular ionisation alone grossly overestimates the measured currents when parameters previously suggested in the literature for mineral oil are used. Preliminary model parameters for these mechanisms that best fit the conduction currents measured in mineral oil are presented and discussed.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD , 2019. Vol. 3, no 3, article id UNSP 035019
Keywords [en]
electrical conduction, electrohydrodynamics, mineral oil, excess carriers, RENZO SE, 1974, PHYSICAL REVIEW A, V9, P2582 ng N. V., 2012, IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION, V19, P1593, NAT A, 1988, IEEE TRANSACTIONS ON ELECTRICAL INSULATION, V23, P545 ang J. George, 2012, IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION, V19, P162 ten P, 1996, IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION, V3, P1 rrow R, 1999, JOURNAL OF PHYSICS D-APPLIED PHYSICS, V32, PL20 nas, 2006, Nytro 10X Safety Data Sheet, P1, VINS JC, 1981, JOURNAL OF APPLIED PHYSICS, V52, P4531 rbes Richard G., 2007, PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, V463, P2907 nat A., 2006, IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION15th IEEE International Conference on Dielectric Liquids, JUN 26-JUL 01, 2005, Coimbra, PORTUGAL, V13, P518 tcher M, 2006, IEEE TRANSACTIONS ON PLASMA SCIENCE, V34, P467
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-249818DOI: 10.1088/2399-6528/ab0d59ISI: 000463117800019OAI: oai:DiVA.org:kth-249818DiVA, id: diva2:1306195
Note

QC 20190423

Available from: 2019-04-23 Created: 2019-04-23 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, Marley

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