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CONTENTS

CONTENTS 

PREFACE 

1. INDUCTION MACHINES: AN INTRODUCTION.................................................................. 1 

1.1. Electric energy and induction motors................................................................................... 1 

1.2. A historical touch ................................................................................................................. 2 

1.3. Induction machines in applications ...................................................................................... 3 

1.4. Conclusion ......................................................................................................................... 13 

1.5. References.......................................................................................................................... 13 

2. CONSTRUCTION ASPECTS AND OPERATION PRINCIPLES ......................................... 15 

2.1. Construction aspects of rotary IMs .................................................................................... 16 

2.1.1. The magnetic cores .................................................................................................. 16 

2.1.2. Slot geometry ........................................................................................................... 17 2.1.3. IM windings ............................................................................................................. 19 

2.1.4. Cage rotor windings ................................................................................................. 23 

2.2. Construction aspects of linear induction motors ................................................................ 25 

2.3. Operation principles of IMs ............................................................................................... 27 

2.4. Summary ............................................................................................................................ 31 

2.5. References.......................................................................................................................... 32 

3. MAGNETIC, ELECTRIC, AND INSULATION MATERIALS FOR IM .............................. 33 

3.1. Introduction........................................................................................................................ 33 

3.2. Soft magnetic materials...................................................................................................... 33 

3.3. Core (magnetic) losses ....................................................................................................... 37 

3.4. Electrical conductors.......................................................................................................... 41 

3.5. Insulation materials ............................................................................................................ 43 

3.5.1. Random-wound IM insulation ................................................................................. 44 

3.5.2. Form-wound windings ............................................................................................. 45 

3.6. Summary ............................................................................................................................ 45 

3.7. References.......................................................................................................................... 46 

4. INDUCTION MACHINE WINDINGS AND THEIR MMFs.................................................. 49 

4.1. Introduction........................................................................................................................ 49 

4.2. The ideal traveling mmf of a.c. windings........................................................................... 49 

4.3. A primitive single-layer winding ....................................................................................... 52 

4.4. A primitive two-layer chorded winding ............................................................................. 53 

4.5. The mmf harmonics for integer q....................................................................................... 54 

4.6. Rules for designing practical a.c. windings........................................................................ 58 

4.7. Basic fractional q three-phase a.c. windings ...................................................................... 65 

4.8. Basic pole-changing three-phase a.c. windings ................................................................. 67 

4.9. Two-phase a.c. windings.................................................................................................... 70 

4.10. Pole-changing with single-phase supply induction motors .............................................. 75 

4.11. Special topics on a.c. windings ........................................................................................ 76 

4.12. The mmf of rotor windings .............................................................................................. 82 

4.13. The “skewing” mmf concept ............................................................................................ 83 4.14. Summary .......................................................................................................................... 84 

4.15. References........................................................................................................................ 86 

© 2010 by Taylor and Francis Group, LLC

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5. THE MAGNETIZATION CURVE AND INDUCTANCE...................................................... 87 

5.1. Introduction........................................................................................................................ 87 

5.2. Equivalent airgap to account for slotting ........................................................................... 88 

5.3. Effective stack length......................................................................................................... 90 

5.4. The basic magnetization curve ........................................................................................... 91 

5.4.1. The magnetization curve via the basic magnetic circuit .......................................... 92 5.4.2. Teeth defluxing by slots ........................................................................................... 97 

5.4.3. Third harmonic flux modulation due to saturation................................................... 97 

5.4.4. The analytical iterative model (AIM)....................................................................... 98 

5.5. The emf in an a.c. winding............................................................................................... 109 

5.6. The magnetization inductance.......................................................................................... 112 

5.7. Summary .......................................................................................................................... 116 

5.8. References........................................................................................................................ 117 

6. LEAKAGE INDUCTANCES AND RESISTANCES............................................................ 119 

6.1. Leakage fields .................................................................................................................. 119 

6.2. Differential leakage inductances ...................................................................................... 119 

6.3. Rectangular slot leakage inductance/single layer............................................................. 123 

6.4. Rectangular slot leakage inductance/two layers ............................................................... 125 

6.5. Rounded shape slot leakage inductance/two layers ......................................................... 126 

6.6. Zig-zag airgap leakage inductances ................................................................................. 129 

6.7. End-connection leakage inductance ................................................................................. 131 

6.8. Skewing leakage inductance ............................................................................................ 132 

6.9. Rotor bar and end ring equivalent leakage inductance..................................................... 132 

6.10. Basic phase resistance .................................................................................................... 133 

6.11. The cage rotor resistance................................................................................................ 134 

6.12. Simplified leakage saturation corrections ...................................................................... 135 6.13. Reducing the rotor to stator............................................................................................ 137 

6.14. Summary ........................................................................................................................ 139 

6.15. References...................................................................................................................... 140 

7. STEADY-STATE EQUIVALENT CIRCUIT AND PERFORMANCE................................ 143 

7.1. Basic steady-state equivalent circuit ................................................................................ 143 

7.2. Classification of operation modes .................................................................................... 145 

7.3. Ideal no-load operation .................................................................................................... 146 

7.4. Short-circuit (zero speed) operation................................................................................. 149 

7.5. No-load motor operation .................................................................................................. 153 

7.6. The motor mode of operation........................................................................................... 155 7.7. Generating to power grid ................................................................................................. 156 

7.8. Autonomous induction generator mode ........................................................................... 159 

7.9. The electromagnetic torque.............................................................................................. 161 

7.10. Efficiency and power factor ........................................................................................... 166 

7.11. Phasor diagrams: Standard and new............................................................................... 168 

7.12. Alternative equivalent circuits ....................................................................................... 172 

7.13. Unbalanced supply voltages........................................................................................... 174 

7.14. One stator phase is open................................................................................................. 177 

7.15. Unbalanced rotor windings ............................................................................................ 181 

7.16. One rotor phase is open.................................................................................................. 182 7.17. When voltage varies around rated value ........................................................................ 183 

7.18. When stator voltage have time harmonics ..................................................................... 184 

© 2010 by Taylor and Francis Group, LLC