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SMALL WTND—POWERED ELECTRIC GENERATORS and SYSTEMS Vassilis Clitou Nicodemou, M.Sc. (Eng.) July 1979 a Thesis Submitted

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SMALL WTND—POWERED ELECTRIC GENERATORS and SYSTEMS Vassilis Clitou Nicodemou, M.Sc. (Eng.) July 1979 a Thesis Submitted SMALL WTND—POWERED ELECTRIC GENERATORS AND SYSTEMS by Vassilis Clitou Nicodemou, M.Sc. (Eng.) July 1979 A thesis submitted for the degree of Doctor of Philosophy of the University of London and for the Diploma of Membership of the Imperial College of Science and Technology Department of Electrical Engineering Imperial College of Science and Technology London SW7 2AZ 2. ABSTRACT This thesis examines some electrical aspects of small wind power systems. The first part of the thesis deals briefly with the historical background and with a number of basic technical factors.. associated with wind power exploitation. The second part deals with generators for small wind plants and with aspects of the associated power and control circuits. In the final part, an energy yield estimation method is presented and used to compare a number of different schemes. Most of the second part concerns the design, manufacture_ and test of several specially built P.M. generators, but sections also deal with the operation and performance of generating systems based on wound field and capacitor-excited induction machines. Control and power matching aspects are considered. The four special P.M. machines comprise two low speed designs intended for direct coupling to windmill rotors and two ferrite-field machines designed primarily for operation with step-up transmissions. The disadvantages and advantages of a number of design features including choice of rated speed, P.M. material and layout are detailed. Preliminary results in part three of the thesis seem to show that the use of a P.M. generator increases energy yield by only 5-15% compared with that produced by a carefully-chosen wound field machine and that windmill design, windmill operating mode, site, etc. are likely to be more crucial factors in maximising energy yield per total capital cost. 3, 'ATLcpwµavo 6'6o0c ' yovctt µov xat oXouc oaouc ayacw zdao itoXŪ. Dedicated to my parents and all whom I love 4. "Gt;)cc t.~ ;.c ' Ē)cbe tpa ca)cbv f3o6~ ev0a ūĒ j ux'L%CJ V &Vtl1WV Ya-cgowe )cEXcu&a. xeivov ynp tatitnv rvēµwv 7cotnae Itpovtwv, Bjµ:v ;tr..utilEvat, 1jb' ōpvūµCV, Ov )c ' Ē,9gAtJat v." oi jpoY xep. I: (20). "be (Aeolus) gave it willingly and presented me with a leather bag, made from the flayed skin of a full-grown ox, in which he had imprisoned the boisterous energies of all the Winds. For you must know that Zeus has made him Warden of the Gales, with power to lay or rouse them each at will." Homer, Odysseia, X 5. ACKNOWLEDGEMENTS This work has been carried out under the supervision of Dr. H.R. Bolton. For the invaluable help, inspiration, as well as keen interest, valuable guidance and constant encouragement during the course of the work described in this thesis, the author expresses his sincere gratitude to Dr. Bolton. The author also gratefully acknowledges the valuable and stimulating discussions, useful suggestions and the keen interest maintained during the progress of this work by Dr. L.L. Freris. Thanks are also due to Dr. E.M,Freeman for his continuous encouragement and the active interest he maintained in the project. The author wishes to extend appreciation to all his colleagues in the Electrical Machines and Power Systems Section who kindly revised the typescript of this thesis, and especially to Dr. C. Papageorgiou, Dr. R.A. Ashen and Mr. I.K. Buehring, for their useful discussions and assistance. He would also like to acknowledge the help of Miss. E. Boden throughout the course of this work. The author greatly acknowledges the manufacturing work on the Mark I, Mark II and several test rigs carried out by Mr. R. Moore under the supervision of Mr. C. Jones in the Electrical Engineering Workshop at Imperial College. Thanks are also due to Messrs. R.B. Owen and C. Johnson for their practical assistance and advice during the work. The author wishes to thank'. the British Council and the S.R.C. for financial support of the project and a large number of individuals at Imperial College, Rutherford Laboratory, and elsewhere,, for their help, suggestions and opportunities for discussion. 6. Thanks for financial support are also due to a number of individuals, and in particular my parents. Finally, the author thanks Mr. R. Puddy for drawing the figures and Mrs. S. Murdock for typing the manuscript. 7. LIST OF CONTENTS Page Abstract 2 Acknowledgements 5 List of Contents 7 List of Principal Symbols 13 CHAPTER 1: INTRODUCTION 18 1.1 Brief Historical Review on the Future of Energy, 18 and Wind Power in Particular 1.2 Introduction to the Work described in the Thesis 22 CHAPTER 2: ENERGY RESOURCES AND REQUIREMENTS FOR 23 DOMESTIC APPLICATIONS 2.1 Introduction 23 2.2 Energy Resources and Energy Consumption for 23 Domestic Applications 2.3 Other Applications of Wind-powered Systems 30 CHAPTER 3: MACHINES AND SYSTEMS FOR TRANSFORMATION 36 OF WIND ENERGY INTO ELECTRICAL ENERGY 3.1 Introduction 36 3.2 Wind Power and Windmills 36 3.2.1 Available power in the wind 36 3.2.2 Windmill operation and characteristics 38 3.2.3 Types of windmills 44 3.2.4 Windmills for generation of electricity 49 3.3 Electrical Generators and Systems for Small-Scale 53 Wind Power Application 3.3.1 Effect of operating speed on generator 56 design 3.3.2 Use of special electric generators for 63 small-scale wind-powered systems 3.3.3 Control systems of wind-powered electric 71 generators for maximum extraction of power from the wind 3.4 Capacitor-excited Induction Generator 83 3.4.1 Wind-powered Induction Generator for 88 Maximum Extraction of Wind Power with Variable Capacitor Excitation 3.5 Concluding Remarks 94 8. Page CHAPTER 4: SMALL WIND-POWERED WOUND FIELD GENERATORS 95 4.1 Introduction 95 4.2 Rewinding the Armature of the Lorry Alternator 96 4.2.1 Details of the machine 97 4.2.2 Test rig 98 4.3 Tests on the Lorry Alternator 100 4.4 Results and Comments 102 4.4.1 No-load voltage (e.m.f.) Ef, versus field 102 current at constant rotational speed. (Magnetization curve.) 4.4.2 Iron, windage and friction losses (no-load 102 losses) versus field current at 1500 rev.min1 4.4.3 Armature winding temperature rise 104 4.4.4 Constant speed load characteristics of the 106 machine connected to a.c. and•d.c. resistive loads at 1500 rev.min-1 4.4.5 Load characteristics of the machine connected 111 to a d.c. load through a three-phase, half- controlled rectifier bridge 4.4.6 Effect of field current variation on the load 113 characteristics with and without diode bridge rectification 4.5 Operation with a Self-Excited Shunt-Connected Generator 115 4.5.1 Operation with generator 117 4.5.2 Effect of generator imperfections 121 4.5.3 Ideal performance curves 126 4.5.4 Generation using a self-excited generator 128 4.5.5 Determination of coefficient k 128 4.5.6 Experimental measurements 130 4.6 Field Tests on the Lorry Alternator 137 4.7 Concluding Remarks 139 CHAPTER 5: PERMANENT MAGNET ALTERNATORS: LOW SPEED TYPE WITH 140 CIRCUMFERENTIALLY-ORIENTATED PERMANENT MAGNETS ON THE ROTOR 5.1 Introduction 140 5.2 Review of Literature relating to Permanent Magnet Machines 140 5.3 Choice of Principal Features of the First Experimental 145 Generator for Wind Power Application 9. Page 5.4 Construction of the Mark I Circumferential Rotor 151 Permanent Magnet (P.M.) Alternator 5.4.1 Stator 151 5.4.2 Rotor 153 5.5 Theory 159 5.5.1 Geometry of the alternator 160 5.5.2 The equivalent circuit and phasor diagram of 162 the CRPMA connected to a resistive load 5.5.3 Calculation of the current I and voltage V 166 of the alternator from its phasor diagram 5.5.4 Synchronous reactances of the machine 169 5.5.5 Calculation of the direct-axis magnetizing 172 reactance X ad 5.5.6 Calculation of the quadrature-axis magnetizing 175 reactance X aq 5.5.7 Inductive leakage reactance of the alternator Xe 175 5.5.8 The resistance of the winding of the alternator 176 5.5.9 Equivalent magnetic circuit of the circumferential 177 rotor p.m. alternator at no-load 5.5.10, Magnetic circuit of the alternator and the 183 calculation of the resultant flux in the airgap for-on-load conditions 5.5.11 The e.m.f. of the armature winding of the 185 alternator 5.5.12 No-load e.m.f. of the alternator 186 5.5.13 Definition of the direct-axis demagnetizing 188 m.m.f. of a three-phase winding 5.5.14 The resultant e.m.f. in the airgap of the 189 alternator 5.6 Calculation of the Regulation, Output Power Curves, Load 191 Angle EL and Efficiency Characteristics of the Machine 5.7 Theoretical and Experimental .Results and their Correlation 192 5.8 Saturation of the Stator Teeth of the Alternator and its 197 Influence on the Performance 5.8.1 Calculation of the performance of the alternator 203 with lower line of return of the magnet 5.9 Tests on the Mark I P.M. Alternator 208 5.9.1 Test rig 209 5.9.2 Test procedures 211 5.10 Results and Discussion of Actual Performances of the Mark I 215 P.M. Alternator 5.10.1 Section A results (unskewed machine with 20 turns 215 per coil and an airgap of 0.41 mm) 10. Page 5.10.2 Section B results (unskewed machine with 20 turns 218 per coil and a new airgap of 0.483 mm) 5.10.3 Section C results (skewed machine with 21 turns 221 per coil and the airgap of 0.483 mm) 5.11 Design and Construction of the "Rutherford" Low Speed, 230 Permanent Magnet Alternator 5.11.1 Double—layer fractional—slot windings 236 5.11.2 Design of the double—layer fractional—slot 238 winding of the "Rutherford" p.m.
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