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A Loss Model and Finite Element Analyses of the Influence of Load Angle Oscillation on Stator Eddy Current Losses in a Synchronous Generator
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Hydro Power at the Division for Electricity)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Hydro Power at the Division for Electricity)
2017 (English)In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069Article in journal (Refereed) Submitted
Abstract [en]

The load angle of a synchronous generator connected to a power grid has an eigenfrequency that depends on the operating conditions. The existence of an eigenfrequency can make the generator sensitive to electrical and mechanical disturbances and motivates the use of damper windings and power stabilizing systems. The eddy current losses in the stator core and clamping structure increase as a consequence of the load angle oscillations. This is shown both with transient finite element analyses and analytically via a loss model derived from a steady state phasor model of the eddy current loss density. The model is also applicable to the quasi-steady states occurring during load angle oscillations.

Place, publisher, year, edition, pages
2017.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-331176OAI: oai:DiVA.org:uu-331176DiVA: diva2:1148632
Available from: 2017-10-11 Created: 2017-10-11 Last updated: 2017-10-17
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: 2017-11-07

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