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Axial Magnetic Fields at the Ends of a Synchronous Generator at Different Points of Operation
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2015 (English)In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 51, no 2, 8100208Article in journal (Refereed) Published
Abstract [en]

Axial magnetic fields leaking out at the ends of a conventional rotating synchronous machine cause losses. Therefore, it is important to be able to predict the axial magnetic fields. A linear steady-state model for the axial magnetic flux density phasor in the end regions of non-salient synchronous generators has previously been verified experimentally. This paper describes an extension of the model to salient pole synchronous generators and a method for calculating the coefficients. Experiments and 3-D finite element simulations justify a distinction between axial flux density contributions from the d and q components of the stator current. How the coefficients and the axial magnetic fields in the ends of a small synchronous generator change with steady-state operation conditions is here shown with measurements and to some extent with 3-D finite element simulations.

Place, publisher, year, edition, pages
2015. Vol. 51, no 2, 8100208
Keyword [en]
Axial magnetic flux, hydropower generator, operation conditions
National Category
Physical Sciences Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-255312DOI: 10.1109/TMAG.2014.2347269ISI: 000353595800015OAI: oai:DiVA.org:uu-255312DiVA: diva2:822414
Available from: 2015-06-16 Created: 2015-06-15 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Magnetic Leakage Fields and End Region Eddy Current Power Losses in Synchronous Generators
Open this publication in new window or tab >>Magnetic Leakage Fields and End Region Eddy Current Power Losses in Synchronous Generators
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The conversion of mechanical energy to electrical energy is done mainly with synchronous generators. They are used in hydropower generators and nuclear plants that presently account for about 80% of the electric energy production in Sweden. Because of the dominating role of the synchronous generators, it is important to minimize the power losses for efficient use of natural resources and for the economies of the electric power companies and their customers. For a synchronous machine, power loss means undesired heat production. In electric machines, there are power losses due to windage, friction in bearings, resistance in windings, remagnetization of ferromagnetic materials, and induced voltages in windings, shields and parts that are conductive but ideally should be non-conductive.

The subject of this thesis is prediction of end region magnetic leakage fields in synchronous generators and the eddy current power losses they cause. The leakage fields also increase the hysteresis losses in the end regions. Magnetic flux that takes paths such that eddy current power losses increase in end regions of synchronous generators is considered to be leakage flux. Although only a small fraction of the total magnetic flux is end region leakage flux, it can cause hot spots, discoloration and reduce the service life of the insulation on the core laminations. If unattended, damaged insulation could lead to electric contact and eddy currents induced by the main flux between the outermost laminations. That gives further heating and deterioration of the insulation of laminations deeper into the core. In a severe case, the core can melt locally, cause a cavity, buckling and a short circuit of the main conductors. The whole stator may have to be replaced. However, the end region leakage flux primarily causes heating close to the main stator conductors which makes the damage possible to discover by visual inspection before it has become irrepairable.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 76 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1575
Keyword
magnetic leakage fields, leakage flux, eddy currents, losses, synchronous generator
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Mathematical Analysis
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-331182 (URN)978-91-513-0103-7 (ISBN)
Public defence
2017-11-30, Room 2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2017-11-07 Created: 2017-10-11 Last updated: 2017-11-24

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Marcusson, BirgerLundin, Urban

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