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Reduction of unbalanced magnetic pull in synchronous machines due to parallel circuits
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.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2011 (English)In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 47, no 12, 4827-4833 p.Article in journal (Refereed) Published
Abstract [en]

This paper describes an analysis of the damping of unbalanced magnetic pull (UMP) in salient pole synchronous machines due to parallel stator circuits. Measurements of the UMP and currents in the parallel circuits have been performed on a 12-pole generator with the stator displaced relative to the rotor, creating a static eccentricity, and the stator winding connected as one circuit or two parallel circuits. Experiments were done at no-load conditions. Two numerical studies of the force reduction are also presented, one using a finite-element code and one using a permeance model. A good correspondence between measured and simulated forces is obtained. Results indicate that the reduction of UMP is strongly dependent on the direction of unbalance relative to the line of separation of the stator circuits. Eddy currents induced in the rotor during operation were found to reduce the standstill UMP with more than 20%.

Place, publisher, year, edition, pages
2011. Vol. 47, no 12, 4827-4833 p.
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-146615DOI: 10.1109/TMAG.2011.2160727ISI: 000297337400021OAI: oai:DiVA.org:uu-146615DiVA: diva2:398555
Available from: 2011-02-18 Created: 2011-02-18 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Electromagnetic Analysis of Hydroelectric Generators
Open this publication in new window or tab >>Electromagnetic Analysis of Hydroelectric Generators
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Elektromagnetisk analys av vattenkraftgeneratorer
Abstract [en]

Hydropower maintains its position as the most important source of renewable electric energy in the world. The efficiency of large hydropower plants is unsurpassed, and after more than hundred years of development, the technology is mature and highly reliable. While new hydro resources are currently being developed in Asia and South America, most European countries go through a phase of intense refurbishment and upgrading of existing plants. Challenges faced by the hydropower industry include a knowledge transfer to new generations and the adaptation of unit designs to meet new operational requirements.

As with all branches of engineering, the use of computerized design tools has revolutionized the art of hydropower plant design and the analysis of its performance. In the present work, modern tools like coupled field-circuit models and semi-analytic permeance models are used to address different aspects of electromagnetic analysis of generators in large hydropower plants.

The results include the presentation of a mathematical model that uses concepts from rotating field theory to determine the air-gap flux density waveform in a hydroelectric generator. The model was succesfully used to evaluate armature voltage harmonics and damper bar currents at no-load and load conditions.

A second study is concerned with the importance of losses due to rotational fields in core loss calculations. It is found that dynamic and rotational effects typically increase the total core loss estimates with about 28% in large hydroelectric generators.

In a third study, linear models for the calculation of salient pole shoe form factors at an arbitrary level of magnetic loading are presented. The effect of the damper winding configuration on the damping capability of salient-pole generators is then evaluated in a separate study. The predicted impact of the coupling between damper cages on adjacent poles on the damping torque production is verified in a set of experiments.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 118 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 810
Keyword
Contra-rotating rotors, damping torque, damper winding, finite element method, hydroelectric generators, permeance model, pole shoe shape, rotational losses, single machine infinite bus, slot ripple, synchronizing torque, synchronous machines, voltage waveform.
National Category
Other Engineering and Technologies
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-146629 (URN)978-91-554-8027-1 (ISBN)
Public defence
2011-05-06, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2011-04-07 Created: 2011-02-18 Last updated: 2012-10-05Bibliographically approved
2. Measurement and modelling of unbalanced magnetic pull in hydropower generators
Open this publication in new window or tab >>Measurement and modelling of unbalanced magnetic pull in hydropower generators
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hydropower research is often perceived to be an old and exhausted field of study but with ageing equipment and the need for more intermittent operation caused by an increased share of other renewable energy sources new challenges lie ahead.

The main focus of this dissertation are the electromagnetic forces resulting from nonuniform air gap flux, whether it be caused by rotor eccentricity or a faulty field winding. Results are predominantly obtained from measurements on an experimental generator and numerical simulations.

With the computational capacity available today it is possible to numerically analyse physical phenomena that previously could only be studied with analytical tools. Numerical models can also be expanded to encompass more than one aspect of generator operation in coupled field-circuit models without model complexity surpassing computer capability.

Three studies of unbalanced magnetic pull, UMP, in synchronous salient pole generators constitute the main part of this thesis.

The first is a study of how parallel stator circuits affect the unbalanced magnetic pull caused by rotor eccentricity. Depending on the relationship between the geometry of the separate circuits and the direction of the eccentricity it was found that parallel circuits could reduce the UMP substantially.

Secondly, an investigation of the effect of damper winding configuration on UMP was performed. The results showed that damper winding resistivity and the distance between the damper bars in a pole determine the effectiveness of the damper winding in reducing the UMP. Simulations of a production machine indicate that the reduction can be substantial from damper windings with low resistivity.

The third study analyses the consequences of field winding interturn short circuits. Apart from a resulting rotating unbalanced magnetic pull it is found that the unaffected poles with the same polarity as the affected pole experience an increase in flux density.

In a fourth article a new stand still frequency response, SSFR, test method including measurements of damper winding voltage and current is presented. It is found that the identified models are capable of predicting the stator to damper transfer function both with and without the damper winding measurements included.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 51 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1029
Keyword
Damper winding, eddy currents, field winding short circuit, finite element method, hydropower generator, parallel circuits, rotor eccentricity, salient poles, synchronous generators, synchronous machines, UMP, unbalanced magnetic pull.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-196490 (URN)978-91-554-8619-8 (ISBN)
Public defence
2013-04-26, Polhemssalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2013-04-05 Created: 2013-03-10 Last updated: 2013-08-30Bibliographically approved

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Wallin, MattiasRanlöf, MartinLundin, Urban

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