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  • ROEBEL WINDINGS FOR HYDRO GENERATORS

    Thesis for the Master of Science (MSc) degree Poopak Roshanfekr Fard

    Division of Electric Power Engineering Department of Energy & Environment CHALMERS UNIVERSITY OF TECHNOLOGY Gteborg, Sweden 2007

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    ROEBEL WINDINGS FOR HYDRO GENERATORS

    Poopak Roshanfekr Fard

    Division of Electric Power Engineering Department of Energy & Environment

    CHALMERS UNIVERSITY OF TECHNOLOGY Gteborg, Sweden, 2007

    Department of Energy & Environment Chalmers University of Technology Gteborg, Sweden, 2007 Proposed & Sponsored by: ABB Performed at: Chalmers University of Technology Gteborg, Sweden Supervisor & Examiner: Dr. Sonja Tidblad Lundmark Division of Electric Power Engineering Department of Energy & Environment Chalmers University of Technology

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    ACKNOWLEDGEMENTS This thesis work has been carried out at the Division of Electric Power Engineering, Chalmers University of Technology. I would like to express my special thanks to my supervisor, Dr. Sonja Tidblad Lundmark who has not only enlightened me with her courses at Chalmers University of Technology but also actively participated to complete this thesis work. Her technical insight, advice and patient guidance are gratefully appreciated. The financial support granted by ABB AB Corporate Research is gratefully acknowledged. I am also indebted to Mr. Bengt Rothman and Dr. Waqas Arshad at ABB for their help. Many thanks go to all the members of the Division of Electric Power Engineering at Chalmers University of Technology who shared their knowledge with me. Last but not the least, I wish to thank my family, in particular my dear brother Siamak for his special support during the period of study at Chalmers University of Technology. For all your help I need to say:

    Thank You.

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    ABSTRACT Large-scale generators tend to have high power. Normally, the armature winding of these generators consist of multiple strands insulated separately and transposed (using Roebel transposition) in order to suppress losses caused by eddy currents and circulating currents. As the generator reaches high power density, circulating currents in the armature winding are large, and hence the loss must be estimated accurately in generator design. Calculation of such losses requires the distribution of circulating currents, which differs from strand to strand. The Roebel bar optimum structure allows increasing machine efficiency, and consequently energy savings. In this thesis, the circulating currents in a Roebel transposed diamond coil have been studied. The Roebel transposition in the active part of the generator have been 180 and 360. Moreover the circulating currents for a traditional Roebel bar (no transposition at the end region) and for a Roebel bar with transposition at the end region has been carried out. Finally the values of circulating currents and the losses due to these currents for these Roebel bars have been compared. The study has been carried out using models of the winding developed in a FEM-program package. A 2D model of the active part has been drawn in MagNet. From the flux linkages that are taken from the program the circulating currents has been calculated analytically. A 3D model of the end region of the winding has been drawn in MagNet and the fields of this region has been studied. The circulating currents in half a coil has been investigated from the results obtained from the 2D and 3D simulations. The conclusions of the study are that using 360 transposition in the active part reduces the circulating currents almost to zero. 180 transposition reduces the circulating current. The study further concludes that using transposition in the end region reduces the circulating currents in the bar. Finally the study concludes that the minimum circulating current loss is achieved in case of 360 transposition in the active part (slot region) and transposition in the end region. It is also shown a cost-effective well chosen manufacturing process. Key Words: Roebel bar, Circulating currents, 360 transposition, 180 transposition, active part (slot region), end region, 2D finite element method (FEM), 3D finite element method (FEM)

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    Table of Contents ACKNOWLEDGEMENTS............................................................................................... iii ABSTRACT.......................................................................................................................... v Table of Contents............................................................................................................... vi 1. INTRODUCTION .......................................................................................................... 1

    1.1. Objective of the Thesis ............................................................................................ 1 1.2. Outline of the Thesis Report .................................................................................... 1

    2. THEORETICAL BACKGROUND................................................................................ 3 2.1. Armture Winding Configuration.............................................................................. 3 2.2. Roebel Bars.............................................................................................................. 3

    2.2.1. Transposition in the slot region......................................................................... 4 2.2.2. Transposition in the end region......................................................................... 5

    2.3. Analysis of strand currents in slot region ................................................................ 5 2.3.1. Analysis of strand currents in slot region at 360 transposition ....................... 6 2.3.2. Analysis of strand currents in slot region at 180 transposition ....................... 9

    2.4. Strand circuit .......................................................................................................... 10 2.5. Circuit equations .................................................................................................... 10

    2.5.1. Unknown being strand current........................................................................ 11 2.5.2. Unknown being the circulating current........................................................... 12 2.5.3. Selection of unknowns in circuit equations .................................................... 13

    2.6. Magnetic Flux Linkage in the strands.................................................................... 15 2.7. Analysis of strand currents in half coils................................................................. 15 2.8. Resistance .............................................................................................................. 16 2.9. Inductance .............................................................................................................. 16

    3. SIMULATION OF SLOT REGION ............................................................................ 17 3.1. Simulated model .................................................................................................... 17

    3.1.1. Boundary conditions ....................................................................................... 18 3.2. Inductance calculation ........................................................................................... 18

    3.2.1. Phase current ................................................................................................... 18 3.3. Resistance .............................................................................................................. 19 3.4. External flux........................................................................................................... 19

    3.4.1. Radial flux....................................................................................................... 19 3.4.2. Transversal flux .............................................................................................. 20 3.4.3. Circulating current due to radial and transversal flux before transposition.... 20 3.4.4. Circulating current after transposition ............................................................ 22

    3.5. Internal flux............................................................................................................ 24 3.6. External & Internal flux ......................................................................................... 25

    3.6.1. Circulating current due to internal and external flux after applying transposition.............................................................................................................. 25

    4. SIMULATION OF END REGION .............................................................................. 27 4.1. End winding without transposition ........................................................................ 27

    4.1.1. Boundary conditions ....................................................................................... 28 4.1.2. Inductance calculation .................................................................................... 28 4.1.3. Resistance ....................................................................................................... 28 4.1.4. External flux.................................................................................................... 29

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    4.1.5. Circumferential external flux.......................................................................... 29 4.1.6. Internal flux...................................................................................

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