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Cellulose-based electrical insulation materials: Dielectric and mechanical properties
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.ORCID iD: 0000-0002-1924-6954
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. , p. 63
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2017:21
Keywords [en]
cellulose, dielectric materials, electrical insulation, nanocellulose, nanoparticles, streamer
National Category
Polymer Technologies
Research subject
Fibre and Polymer Science
Identifiers
URN: urn:nbn:se:kth:diva-205622ISBN: 978-91-7729-327-9 (print)OAI: oai:DiVA.org:kth-205622DiVA, id: diva2:1089609
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
List of papers
1. Dielectric properties of lignin and glucomannan as determined by spectroscopic ellipsometry and Lifshitz estimates of non-retarded Hamaker constants
Open this publication in new window or tab >>Dielectric properties of lignin and glucomannan as determined by spectroscopic ellipsometry and Lifshitz estimates of non-retarded Hamaker constants
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2013 (English)In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 20, no 4, p. 1639-1648Article in journal (Refereed) Published
Abstract [en]

We present in this study a quantitative estimate of the dispersive interactions between lignin, hemicellulose and cellulose, which are the dominating components in wood and also extensively used to produce paper and packaging materials. The dielectric properties in the UV-visible region of spin-coated films of pure lignin and glucomannan were determined by spectroscopic ellipsometry. The non-retarded Hamaker constants were estimated from the determined spectral parameters using Lifshitz theory for lignin and glucomannan interacting with cellulose, titania and calcium carbonate in vacuum, water and hexane. The Hamaker constants for the different combinations of cellulose, lignin and glucomannan fall within a relatively narrow range of 35-58 and 8-17 zJ, for the values in vacuum (air) and water, respectively. The estimated Hamaker constants for the interactions of the wood components with TiO2 and CaCO3, common additives in paper, in water range from 3 to 19 zJ, thus being similar in magnitude as the interactions between the wood components themselves. In contrast, the Hamaker constant is essentially zero for glucomannan interacting with calcium carbonate in hexane. The Hamaker constants for lignin, hemicellulose and cellulose determined in this study can provide information regarding the surface interactions important for e.g. adhesion, friction, swelling and wetting in paper processing as well as for the resulting behavior of paper products.

Keywords
Glucomannan, Lignin, Cellulose, Spectroscopic ellipsometry, Dispersion forces, Hamaker constant
National Category
Other Chemistry Topics Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-132212 (URN)10.1007/s10570-013-9980-9 (DOI)000322673000009 ()2-s2.0-84881028455 (Scopus ID)
Funder
Swedish Energy AgencySwedish Foundation for Strategic Research
Note

QC 20131024

Available from: 2013-10-24 Created: 2013-10-24 Last updated: 2017-12-06Bibliographically approved
2. Effect of Composition and Morphology on the Dielectric Response of Cellulose-based Electrical Insulation
Open this publication in new window or tab >>Effect of Composition and Morphology on the Dielectric Response of Cellulose-based Electrical Insulation
2015 (English)In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 22, no 4, p. 2339-2348Article 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.

Keywords
Paper insulation, interconnected systems, dielectric materials, permittivity, dielectric losses, dielectric measurements, dielectric polarization, cellulose, hemicellulose, lignin
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-173279 (URN)10.1109/TDEI.2015.005017 (DOI)000359591600072 ()2-s2.0-84939557888 (Scopus ID)
Note

QC 20150909

Available from: 2015-09-09 Created: 2015-09-09 Last updated: 2017-12-04Bibliographically approved
3. First mode negative streamers at mineral oil-solid interfaces
Open this publication in new window or tab >>First mode negative streamers at mineral oil-solid interfaces
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(English)Manuscript (preprint) (Other academic)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-205618 (URN)
Note

QC 20170424

Available from: 2017-04-20 Created: 2017-04-20 Last updated: 2017-04-27Bibliographically approved
4. Inception of first mode negative streamers at mineral oil-solid interfaces
Open this publication in new window or tab >>Inception of first mode negative streamers at mineral oil-solid interfaces
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(English)Manuscript (preprint) (Other academic)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-205619 (URN)
Note

QC 20170424

Available from: 2017-04-20 Created: 2017-04-20 Last updated: 2017-04-27Bibliographically approved
5. Influence of paper properties on streamers creeping in mineral oil
Open this publication in new window or tab >>Influence of paper properties on streamers creeping in mineral oil
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(English)Manuscript (preprint) (Other academic)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-205621 (URN)
Note

QC 20170424

Available from: 2017-04-20 Created: 2017-04-20 Last updated: 2017-04-27Bibliographically approved
6. Chemically modified cellulose micro- and nanofibrils as paper-strength additives
Open this publication in new window or tab >>Chemically modified cellulose micro- and nanofibrils as paper-strength additives
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-205620 (URN)
Note

QC 20170424

Available from: 2017-04-20 Created: 2017-04-20 Last updated: 2017-04-26Bibliographically approved
7. Dielectric Response of Kraft Paper from Fibres Modified by Silica Nanoparticles
Open this publication in new window or tab >>Dielectric Response of Kraft Paper from Fibres Modified by Silica Nanoparticles
2015 (English)In: 2015 IEEE CONFERENCE ON ELECTRICAL INSULATION AND DIELECTRIC PHENOMENA (CEIDP), IEEE conference proceedings, 2015, p. 459-462Conference paper, Published paper (Refereed)
Abstract [en]

Papers have been prepared from fibres that were modified by physical adsorption of silica nanoparticles. Cationic and anionic nanoparticles were adsorbed either directly onto wood fibres or using the layer-by-Iayer (LbL) technique where silica nanoparticles and a polyelectrolyte of opposite charge were adsorbed in consecutive layers. It was shown that it is possible to tailor the dielectric and mechanical properties of kraft paper by utilizing the pH-dependence of the charge density of both the nanoparticles and the polyelectrolyte during the build-up of layers onto wood fibres. With only one layer of cationic silica nanoparticles, 6.0 wt% of nanoparticles were adsorbed at pH 6, leading to almost complete coverage of the wood fibre surface, resulting in a paper with low dielectric losses and improved in-plane tensile properties.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2015
Series
Conference on Electrical Insulation and Dielectric Phenomena Annual Report, ISSN 0084-9162
Keywords
silica nanoparticles, kraft-paper, electrical insulation, dielectric response
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-183709 (URN)10.1109/CEIDP.2015.7351987 (DOI)000370070700094 ()2-s2.0-84959555822 (Scopus ID)978-1-4673-7498-9 (ISBN)
Conference
IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), OCT 18-21, 2015, Ann Arbor, MI
Note

QC 20160318

Available from: 2016-03-18 Created: 2016-03-18 Last updated: 2017-04-20Bibliographically approved
8. Surface Discharge Characteristics of Oil-impregnated Paper with SiO2 and ZnO nanoparticles under AC with Superimposed Impulse
Open this publication in new window or tab >>Surface Discharge Characteristics of Oil-impregnated Paper with SiO2 and ZnO nanoparticles under AC with Superimposed Impulse
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(English)Manuscript (preprint) (Other academic)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-187628 (URN)
Note

QC 20160608

Available from: 2016-05-25 Created: 2016-05-25 Last updated: 2017-04-20Bibliographically approved

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