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First-order perturbation approach to elliptic winding deformations
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.ORCID iD: 0000-0001-9241-8030
2013 (English)In: 2013 International Symposium on Electromagnetic Theory, EMTS 2013 - Proceedings, IEEE , 2013, 13-16 p.Conference paper, Published paper (Refereed)
Abstract [en]

We apply a novel on-line method to detect elliptic deformations of winding turns in a power transformer. We employ the first-order perturbation theory to a transformer winding surrounded by the transformer tank wall and the magnetic core. The transformer winding is modeled as a structure consisting of thin conducting cylindrical rings (winding segments or turns) situated within a coaxial cylindrical waveguide, where the inner conducting cylinder represents the magnetic core and the outer conducting cylinder represents the wall of the transformer tank. We simulate antennas inside the transformer tank to radiate and measure microwave fields, in order to identify and quantify elliptic deformations of the individual winding segments or individual turns. The propagation problem is solved by conventional waveguide theory, including mode-matching and cascading techniques. We utilize optimization to solve the inverse problem and obtain a good agreement between the reconstructed and true deformations of the winding segments.

Place, publisher, year, edition, pages
IEEE , 2013. 13-16 p.
Series
URSI International Symposium on Electromagnetic Theory, ISSN 2163-405X
Keyword [en]
Cascading technique, Conducting cylinder, First-order perturbation theory, Microwave field, Perturbation approach, Transformer tanks, Waveguide theory, Winding deformations
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-129763ISI: 000327180500005Scopus ID: 2-s2.0-84883220077ISBN: 978-1-4673-4939-0 (print)OAI: oai:DiVA.org:kth-129763DiVA: diva2:653591
Conference
2013 21st International Symposium on Electromagnetic Theory, EMTS 2013; Hiroshima; Japan; 20 May 2013 through 24 May 2013
Note

QC 20131004

Available from: 2013-10-04 Created: 2013-10-04 Last updated: 2013-12-20Bibliographically approved
In thesis
1. Online power transformer diagnostics using multiple modes of microwave radiation
Open this publication in new window or tab >>Online power transformer diagnostics using multiple modes of microwave radiation
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In the present thesis, we propose and investigate a new approach to diagnose the effects of the various degradation mechanisms, including thermal degradation at hot spots, winding deformations due to the mechanical forces from short circuit currents, partial discharges due to local electric field surges, and increased moisture levels in the cellulose insulation due to decomposition, that affect electric power transformers during their normal operation in an electric power grid.

Although the proposed diagnostics method can in principle be used to detect various degradation mechanisms mentioned above, we focus in the present thesis on mechanical deformations of transformer winding structures. Such mechanical deformations are most often caused by mechanical forces from short circuit currents, but they may also be caused by initial manufacturing errors and inconsistencies not detected by the power transformers’ suppliers quality assurance processes.

We model a transformer winding surrounded by the transformer-tank wall and the magnetic core as a two-dimensional parallel plate waveguide or as a three-dimensional coaxial waveguide, where one metallic boundary (plate or cylinder) represents the wall of the transformer tank and the other metallic boundary (plate or cylinder) represents the iron core that conducts the magnetic flux. In between there is a set of parallel or coaxial conductors representing the winding segments.

The new principle proposed in the present thesis is to insert a number of antennas into a transformer tank to radiate and measure microwave fields interacting with metallic structures and insulation. The responses from the emitted microwave radiation are expected to be sensitive to material properties that reflect the changes caused by any harmful deterioration processes mentioned above. Specifically, we investigate the mechanical deformations of transformer winding structures by determining the locations of the individual winding segments or turns, using measurements of the scattered fields at both ends of the winding structure. We solve the propagation problem using conventional waveguide theory, including mode-matching and cascading techniques.

The inverse problem is solved using modified steepest-descent optimization methods. The optimization model is tested by comparing our calculated scattering data with synthetic measurement data generated by the commercial program HFSS.

A good agreement is obtained between the calculated and measured positions of winding segments for a number of studied cases, which indicates that the diagnostics method proposed in the present thesis couldbe potentially useful as a basis for the design of a future commercial on-line winding monitoring device. However, further development of the theoretical analysis of a number of typical winding deformations, improvements of the optimization algorithms and a practical study with measurements on an actual power transformer structure are all needed to make an attempt to design a commercial winding monitoring device feasible.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. x, 93 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2013:033
Keyword
inverse problem; multiple modes; power transformers
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-129766 (URN)978-91-7501-832-4 (ISBN)
Presentation
2013-10-25, H1, Teknikringen 33, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20131007

Available from: 2013-10-07 Created: 2013-10-04 Last updated: 2016-02-24Bibliographically approved

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Norgren, Martin

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