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Electromagnetic Analysis of Hydroelectric Generators
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Elektromagnetisk analys av vattenkraftgeneratorer (Swedish)
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 [en]
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: urn:nbn:se:uu:diva-146629ISBN: 978-91-554-8027-1OAI: oai:DiVA.org:uu-146629DiVA: diva2:398596
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
List of papers
1. On Permeance Modeling of Large Hydrogenerators With Application to Voltage Harmonics Prediction
Open this publication in new window or tab >>On Permeance Modeling of Large Hydrogenerators With Application to Voltage Harmonics Prediction
2010 (English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 25, no 4, 1179-1186 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, a permeance model that can be employed to estimate the no-load damper current loss and voltage waveform harmonics in large hydrogenerators is presented. The importance of modeling the damper magnetomotive force and inductances correctly is emphasized, and detailed descriptions are presented. The computed harmonics are compared with values obtained from time-stepped finite-element calculations and measured data. The results are in good agreement. The influence of pole-to-pole damper bar connections, and of the number of damper bars on the voltage waveform, is explained.

Keyword
Damper winding, hydroelectric generators, permeance model, slot ripple, voltage waveform
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-139403 (URN)10.1109/TEC.2010.2040740 (DOI)000284415900029 ()
Available from: 2010-12-27 Created: 2010-12-23 Last updated: 2016-04-19Bibliographically approved
2. The Rotating Field Method Applied to Damper Loss Calculation in Large Hydrogenerators
Open this publication in new window or tab >>The Rotating Field Method Applied to Damper Loss Calculation in Large Hydrogenerators
2010 (English)Conference paper (Refereed)
Abstract [en]

In this paper, we discuss key aspects of analytical rotating field models that can be used to estimate the damper losses in large hydrogenerators during steady load conditions. Model features of particular importance, like the saturation permeance and the structure of the damper circuit are described in greater detail. Damper currents extracted from the analytic model are found to be in good agreement with currents obtained from coupled field-circuit 2-D finite element calculations. The applicability of the model for damper current prediction during steady unbalanced load conditions is also demonstrated.

Place, publisher, year, edition, pages
Rome, Italy: , 2010
Keyword
Damper winding, hydroelectric generators, losses, permeance model, rotating field method.
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-142511 (URN)10.1109/ICELMACH.2010.5607695 (DOI)
Conference
XIX International Conference on Electrical Machines (ICEM)
Available from: 2011-01-14 Created: 2011-01-14 Last updated: 2016-04-18Bibliographically approved
3. 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: 2016-04-20Bibliographically approved
4. Core Loss Prediction in Large Hydropower Generators: Influence of Rotational Fields
Open this publication in new window or tab >>Core Loss Prediction in Large Hydropower Generators: Influence of Rotational Fields
2009 (English)In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 45, no 8, 3200-3206 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, we discuss the accuracy of several core loss models as compared to experimental data obtained from measurements on commercial hydropower generators. Our aim in this paper is twofold. First, we emphasize the problem of total core loss prediction by comparing the core loss figures obtained by different loss prediction schemes with measured no-load losses. Second, we examine the predicted net effect of bidirectional flux, i.e., the rotational loss. We show that the average degree of rotation in the stator core, and hence the rotational loss, is closely related to the stator slot geometry.

Place, publisher, year, edition, pages
USA: IEEE, 2009
Keyword
Hydropower generators, iron losses, loss separation, rotational losses, synchronous machines
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113155 (URN)10.1109/TMAG.2009.2019115 (DOI)000268282500019 ()0018-9464 (ISBN)
Note

10792786 hydropower generators core loss prediction rotational fields predicted net effect bidirectional flux rotational loss stator core stator slot geometry

Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2016-04-14Bibliographically approved
5. Form Factors and Harmonic Imprint of Salient Pole Shoes in Large Synchronous Machines
Open this publication in new window or tab >>Form Factors and Harmonic Imprint of Salient Pole Shoes in Large Synchronous Machines
2011 (English)In: Electric power components and systems, ISSN 1532-5008, E-ISSN 1532-5016, Vol. 39, no 9, 900-916 p.Article in journal (Refereed) Published
Abstract [en]

This article presents a review of the connection between salient pole shoe shapes and form factors that model saliency affects in synchronous machine design programs. Additionally, the impact of the pole shape on the harmonic contents of the air-gap flux density waveform is examined. The properties of different pole shoes are assessed with 2-D finite element analysis in the working environment of a large hydro-electric generator topology. The influence of magnetic saturation is particularly emphasized. Linear models for the calculation of form factors are established. It is concluded that the choice of pole shoe design typically must be a compromise between a high field and direct axis form factor and a low total harmonic distortion.

Keyword
Finite element method, pole shoe shape, salient poles, saturation, synchronous machines.
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-146606 (URN)10.1080/15325008.2010.549545 (DOI)000299937600005 ()
Available from: 2011-02-18 Created: 2011-02-18 Last updated: 2012-04-02Bibliographically approved
6. Finite Element Analysis of a Permanent Magnet Machine with Two Contra-rotating Rotors
Open this publication in new window or tab >>Finite Element Analysis of a Permanent Magnet Machine with Two Contra-rotating Rotors
2009 (English)In: Electric power components and systems, ISSN 1532-5008, E-ISSN 1532-5016, Vol. 37, no 12, 1334-1347 p.Article in journal (Refereed) Published
Abstract [en]

Electrical machines with contra-rotating rotors find applications in direct-drive energy conversion systems and in ship propulsion systems that employ hydraulic machinery with two contra-rotating stages. In this article, the operating characteristics of permanent magnet machines with two contra-rotating rotors moving on opposite sides of a common stator core are studied via two-dimensional finite element analysis. Particular attention is devoted to the special flux distortion patterns that arise in contra-rotating machine topologies. The study suggests that the introduction of a screening iron core between the rotors provides for negligible flux distortion levels during contra-rotating synchronous operation of the two rotors.

Place, publisher, year, edition, pages
Taylor & Francis, 2009
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113156 (URN)10.1080/15325000903055271 (DOI)000273716300004 ()1532-5008 (ISBN)
Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2016-04-14Bibliographically approved
7. Use of a finite element model for the determination of damping and synchronizing torques of hydroelectric generators
Open this publication in new window or tab >>Use of a finite element model for the determination of damping and synchronizing torques of hydroelectric generators
2013 (English)In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 44, no 1, 844-851 p.Article in journal (Refereed) Published
Abstract [en]

Damping and synchronizing torque coefficients are calculated from time-stepped finite element simulations of a hydroelectric generator connected to an infinite busbar. The calculated torque coefficients are compared to those obtained from two-axis equivalent circuit simulations as well as classical analytical expressions. The influence of the damper winding type, and the size and nature of the system disturbance on the damping and synchronizing torques is explored. It is found that a finite element model of a hydroelectric generator typically exhibits both higher damping and synchronizing properties compared to a two-axis circuit equivalent of the same unit. In particular, the damping and synchronizing contributions from a continuous damper winding are substantially higher in the finite element model than in the equivalent circuit model. Moreover, explicit consideration of dynamic iron losses is found to not affect the damping and synchronizing torques predicted by the finite element model.

Keyword
Damping torque, finite element method, single-machine infinite bus system, synchronizing torque, synchronous machines
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-182158 (URN)10.1016/j.ijepes.2012.08.027 (DOI)000311864800094 ()
Available from: 2012-10-04 Created: 2012-10-04 Last updated: 2016-04-21Bibliographically approved
8. Experimental Study of the Effect of Damper Windings on Synchronous Generator Hunting
Open this publication in new window or tab >>Experimental Study of the Effect of Damper Windings on Synchronous Generator Hunting
(English)In: Electric power components and systems, ISSN 1532-5008, E-ISSN 1532-5016Article in journal (Refereed) Submitted
Abstract [en]

The performance of different damper winding designs with respect to the suppression of hunting is studied. The effect of an inter-pole connection between the pole damper cages on the damping capability of a 75 kVA salient-pole synchronous generator is determined experimentally. Results from tests are further compared with transient electromechanical responses obtained in simulations of the test system. The accuracy of the system model as regards electromechanical transient modeling is assessed and specific modeling challenges are highlighted. It is concluded that a high natural damping capability typically is assured if there exists a low-impedance path between the pole damper cages.

Keyword
Damper winding, damping torque, single-machine infinite bus system, synchronous generator
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-146608 (URN)
Available from: 2011-02-18 Created: 2011-02-18 Last updated: 2011-05-05
9. Comparison of field and circuit generator models in single machine infinite bus system simulations
Open this publication in new window or tab >>Comparison of field and circuit generator models in single machine infinite bus system simulations
2010 (English)In: Electrical Machines (ICEM), 2010 XIX International Conference on, 2010Conference paper (Refereed)
Abstract [en]

This paper compares the transient response of a finite element salient pole synchronous generator model connected to an infinite network bus to that of a system model based on an equivalent circuit representation of the machine. The characteristics and operating conditions of the two models are made equal as far as possible by thoroughgoing initiation and by using the finite element model for estimation of the circuit model parameters. It is found that the circuit model underestimates the stiffness and damping properties of the machine in comparison with the electromagnetic model, which largely is believed to be attributable to inadequate representation of the rotor circuits. The results raise questions regarding some common applications of equivalent circuit models.

Keyword
damping, equivalent circuits, finite element analysis, rotors, synchronous generators, transient response, circuit generator model, circuit model parameter estimation, electromagnetic model, equivalent circuit representation, field generator model, finite element salient pole synchronous generator model, infinite network bus, machine damping property, machine stiffness property, rotor circuit, single machine infinite bus system simulations
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-140377 (URN)10.1109/ICELMACH.2010.5608259 (DOI)
Conference
XIX International Conference on Electrical Machines (ICEM)
Available from: 2011-01-05 Created: 2011-01-05 Last updated: 2016-04-18
10. 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 (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

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