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Effect of Composition and Morphology on the Dielectric Response of Cellulose-based Electrical Insulation
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.ORCID iD: 0000-0001-8622-0386
2015 (English)In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 22, no 4, 2339-2348 p.Article in journal (Refereed) Published
Abstract [en]

Different wood-fibre based papers were characterized by dielectric spectroscopy, mechanical testing and microscopy. The data obtained were utilized to investigate the relationship between the chemistry, morphology and density of a paper and its permittivity and dielectric loss. The density strongly influences the dielectric response, but the response is not affected by the way the density has been achieved; by pressing the paper during drying or by mechanical treatment of the fibres before sheet preparation. The chemical composition of the pulp influences the polarization, dielectric loss and charge transport. It was found that paper-vacuum and paper-oil combinations can be represented by series-equivalent circuits. The permittivity of paper made from electrical grade kraft pulp, used in e.g. high voltage transformers, without any porosity is estimated to be 5.3 and tan delta to 0.01-0.02 at 50 Hz and 70 degrees C. The lignin and hemicellulose content of the kraft pulp do not affect the real part of the permittivity significantly, but the dielectric losses increase with increasing lignin and hemicellulose content in both oil and vacuum at 50 Hz and 70 degrees C.

Place, publisher, year, edition, pages
2015. Vol. 22, no 4, 2339-2348 p.
Keyword [en]
Paper insulation, interconnected systems, dielectric materials, permittivity, dielectric losses, dielectric measurements, dielectric polarization, cellulose, hemicellulose, lignin
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-173279DOI: 10.1109/TDEI.2015.005017ISI: 000359591600072Scopus ID: 2-s2.0-84939557888OAI: oai:DiVA.org:kth-173279DiVA: diva2:852638
Note

QC 20150909

Available from: 2015-09-09 Created: 2015-09-09 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Cellulose-based electrical insulation materials: Dielectric and mechanical properties
Open this publication in new window or tab >>Cellulose-based electrical insulation materials: Dielectric and mechanical properties
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The reliability of the generation and distribution of electricity is highly dependent on electrical insulation and is essential for the prosperity of our society and a ubiquitous part of our everyday life. The present study shows how some important material properties affect the electrical properties of cellulose-based electrical insulation systems which are used together with mineral oil in high-voltage transformers. Among other things, the effects of paper density and of the lignin content of the fibres on the dielectric response and charge transport of the papers have been studied.

The underlying mechanisms of the inception and propagation of streamers, responsible for the most costly failures in transformers, at the oil-solid interface have been investigated and the important role of paper morphology on streamer propagation has been demonstrated. It was also shown that for polymers with permittivities close to that of the oil, the inception voltage was higher than with polymers with higher permittivities.

Fibres were also modified prior to paper sheet preparation in attempts to improve the mechanical and dielectric properties. The properties of papers containing cellulosic micro- and nanofibrils and SiO2 and ZnO nanoparticles indicate that these additives can indeed be used to improve both the mechanical and dielectric properties. For example, a three-layered structure with two papers laminated together with a thin layer of microfibrillated cellulose also showed an increased DC breakdown strength by 47 % compared to a single-layer paper with a similar thickness.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. 63 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2017:21
Keyword
cellulose, dielectric materials, electrical insulation, nanocellulose, nanoparticles, streamer
National Category
Polymer Technologies
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-205622 (URN)978-91-7729-327-9 (ISBN)
Public defence
2017-05-12, F3, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20170420

Available from: 2017-04-20 Created: 2017-04-20 Last updated: 2017-04-25Bibliographically approved

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Wågberg, Lars

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