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Surface Discharge Characteristics of Oil-impregnated Paper with SiO2 and ZnO nanoparticles under AC with Superimposed Impulse
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0002-3310-9964
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.ORCID iD: 0000-0003-0759-4406
Show others and affiliations
(English)Manuscript (preprint) (Other academic)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-187628OAI: oai:DiVA.org:kth-187628DiVA: diva2:930744
Note

QC 20160608

Available from: 2016-05-25 Created: 2016-05-25 Last updated: 2017-04-20Bibliographically approved
In thesis
1. Dielectric Response and Partial Discharge Diagnostics of Insulation Systems by Utilizing High Voltage Impulses
Open this publication in new window or tab >>Dielectric Response and Partial Discharge Diagnostics of Insulation Systems by Utilizing High Voltage Impulses
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, power system transients are considered as an opportunity for development of on-line diagnostics of power components and specifically the insulation systems of power transformers and bushings.

A new technique for on-line dielectric response measurement of power transformer bushings is proposed which utilizes natural transients in the power system, such as lightning and switching surges, as stimuli. Laboratory investigations are done on implementation of the proposed technique. Measurement considerations, data acquisition and processing involved in achievement of reasonable accuracy in the Dielectric Response (DR) are presented. Capability of the technique in tracking of the degradation signatures such as moisture content in the insulation has been evaluated and it has shown a good level of accuracy by being compared to the Frequency Domain Spectroscopy (FDS). 

The proposed technique is tested on the service-aged 150 kV bushings and feasibility of the technique for monitoring of dielectric properties of power transformer bushings has been assessed; the results are promising for the technique to be used in the real application. 

Partial Discharges (PD) behavior under transients has been also studied for different materials in this project. PD behavior of different defects, at different insulation condition, responding to the overvoltage transients in form of superimposed impulses on ac voltages was investigated and it was perceived how their distinctive response and the interpretation of  that, can be useful for their identification.

Besides the conventional materials, surface ac PD properties of modified paper with silica and zinc oxide nanoparticles under the superimposed impulses have been assessed in this project. Proper type and optimum concentration level of nanoparticles in the paper are the factors that lead to the improvement of PD behavior in the modified paper under overvoltage transients.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 79 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2016:080
Keyword
Dielectric Response, Transients, Transformer bushing, Oil-impregnated paper, Moisture content, Partial discharge, Surface PD, Cavity PD, Superimposed impulse, Nanoparticles
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-187632 (URN)978-91-7729-033-9 (ISBN)
Public defence
2016-06-15, sal E3, Osquars backe 14, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20160525

Available from: 2016-05-25 Created: 2016-05-25 Last updated: 2016-06-16Bibliographically approved
2. 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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