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Measurement and modelling of unbalanced magnetic pull in hydropower generators
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Hydropower)
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 [en]
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: urn:nbn:se:uu:diva-196490ISBN: 978-91-554-8619-8 (print)OAI: oai:DiVA.org:uu-196490DiVA: diva2:610339
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
List of papers
1. Design and construction of a synchronous generator test setup
Open this publication in new window or tab >>Design and construction of a synchronous generator test setup
2010 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Rome, Italy: , 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-142512 (URN)10.1109/ICELMACH.2010.5608103 (DOI)
Conference
XIX International Conference on Electrical Machines (ICEM)
Available from: 2011-01-14 Created: 2011-01-14 Last updated: 2016-04-18Bibliographically approved
2. Reduction of unbalanced magnetic pull in synchronous machines due to parallel circuits
Open this publication in new window or tab >>Reduction of unbalanced magnetic pull in synchronous machines due to parallel circuits
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%.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-146615 (URN)10.1109/TMAG.2011.2160727 (DOI)000297337400021 ()
Available from: 2011-02-18 Created: 2011-02-18 Last updated: 2017-12-11Bibliographically approved
3. Damper winding influence on unbalanced magnetic pull in salient pole generators with rotor eccentricity
Open this publication in new window or tab >>Damper winding influence on unbalanced magnetic pull in salient pole generators with rotor eccentricity
2013 (English)In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 49, no 9, 5158-5165 p.Article in journal (Refereed) Published
Abstract [en]

The influence of three different damper winding configurations on unbalancedmagnetic pull (UMP) in salient pole synchronous machines with rotor eccentricity has been investigated. Continuous and noncontinuous damper windings resulted in different damperwinding currents, but their effect on the UMP was found to be very similar. Measurements of the UMP, damper bar currents, and air gap flux density were performed on a 12-pole generator witha static eccentricity under no-load conditions. Finite-element simulations of the different configurations detailing the damper winding induced flux changes are also presented.

Keyword
Damper winding, eddy currents, hydropower generator, rotor eccentricity, synchronous generator, synchronous machine, unbalanced magnetic pull (UMP)
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-196488 (URN)10.1109/TMAG.2013.2259633 (DOI)000323644700028 ()
Available from: 2013-03-10 Created: 2013-03-10 Last updated: 2017-12-06Bibliographically approved
4. Dynamic unbalanced pull from field windingturn short circuits in hydropower generators
Open this publication in new window or tab >>Dynamic unbalanced pull from field windingturn short circuits in hydropower generators
(English)In: Electric power components and systems, ISSN 1532-5008, E-ISSN 1532-5016Article in journal (Refereed) Submitted
Keyword
Hydropower generators, synchronous machines, fault detection, finite element analysis, field winding
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-196489 (URN)
Available from: 2013-03-10 Created: 2013-03-10 Last updated: 2017-12-06Bibliographically approved
5. Standstill Frequency Response Test on a Synchronous Machine Extended With Damper Bar Measurements
Open this publication in new window or tab >>Standstill Frequency Response Test on a Synchronous Machine Extended With Damper Bar Measurements
2016 (English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 31, no 1, 46-56 p.Article in journal (Refereed) Published
Abstract [en]

Standstill Frequency Response (SSFR) test data from a salient-pole synchronous machine with reconfigurable damper winding is presented. In addition to the regular measurements, the damper bar currents are measured and used to obtain the stator-to-damper transfer functions. The test is performed three times with physically different damper winding configurations. An extension to the standard SSFR test analysis scheme is suggested where the stator-to-damper transfer functions are included. The validity of the identified models is substantiated by comparison of the simulated and measured machine response to a drive torque step disturbance. It is found that the damper winding measurements can be incorporated in the analysis scheme to isolate the effect of the damper circuits. However, for a machine of the type studied, also the standard SSFR test produce yields models that are accurate enough for power system studies.

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-182155 (URN)10.1109/TEC.2015.2450994 (DOI)000372024100005 ()
External cooperation:
Available from: 2012-10-04 Created: 2012-10-04 Last updated: 2017-12-07Bibliographically approved

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