Mechanical Design and Manufacturing of Electric Motors

986 Pages·2022·45.265 MB·English

by  Wei Tong

Mechanical Design and
Manufacturing of Electric
Motors
Mechanical Design and
Manufacturing of Electric
Motors
Second Edition
Wei Tong
Second edition published 2022
by CRC Press
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© 2022 Wei Tong
First edition published by CRC Press 2014
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ISBN: 9780367564285 (hbk)
ISBN: 9780367564308 (pbk)
ISBN: 9781003097716 (ebk)
DOI: 10.1201/9781003097716
Typeset in Times
by codeMantra
To my wife, Zhangqing Zhuo, and daughter, Winnie Tong,
for their love, support, and patience.

Contents
Preface (2nd Edition) .......................................................................................................................xxv
Preface (1st Edition) .......................................................................................................................xxix
Author ........................................................................................................................................xxxiii
List of Abbreviations....................................................................................................................xxxv
Chapter 1 Introduction to Electric Motors ....................................................................................1
1.1 H istory of Electric Machines ............................................................................2
1.2 Motor Design Characteristics ............................................................................3
1.2.1 M otor Torque ........................................................................................3
1.2.1.1 Static and Dynamic Torque ..................................................3
1.2.1.2 M otor Torque in Motor-Load System ...................................4
1.2.1.3 C ontinuous Torque ................................................................6
1.2.1.4 P eak Torque ..........................................................................7
1.2.1.5 R MS Torque ..........................................................................7
1.2.1.6 S tall Torque ...........................................................................8
1.2.1.7 Cogging Torque and Reduction Methods .............................8
1.2.1.8 T orque Ripple......................................................................13
1.2.2 M otor Speed .......................................................................................14
1.2.2.1 C ontinuous Speed ...............................................................15
1.2.2.2 P eak Speed ..........................................................................15
1.2.2.3 S peed Ripple .......................................................................15
1.2.3 T orque Density ...................................................................................16
1.2.4 Motor Power and Power Factor ..........................................................16
1.2.5 Torque–Speed Characteristics ............................................................17
1.2.6 M echanical Resonance and Resonant Frequency ..............................20
1.2.7 Load-to-Motor Inertia Ratio...............................................................24
1.2.8 D uty Cycle ..........................................................................................25
1.2.9 M otor Efficiency .................................................................................26
1.2.9.1 Definition of Motor Efficiency ...........................................27
1.2.9.2 IEC Standards on Efficiency Classes of AC
Electric Motors ...................................................................29
1.2.10 Motor Insulation .................................................................................30
1.2.11 Motor Operation Reliability ...............................................................32
1.3 Classifications of Electric Motors ...................................................................32
1.3.1 DC and AC Motors .............................................................................34
1.3.2 Single-Phase and Three-Phase Motors ..............................................37
1.3.3 I nduction and PM Motors ..................................................................37
1.3.4 S ynchronous and Asynchronous Motors ...........................................42
1.3.5 Servo and Stepper Motors ..................................................................44
1.3.6 Gear Drive and Direct Drive Motors .................................................47
1.3.7 Brush and Brushless Motors ..............................................................52
1.3.8 R eluctance Motors ..............................................................................52
1.3.9 Radial Flux and Axial Flux Motors ...................................................53
1.3.10 Rotary and Linear Motors ..................................................................54
1.3.11 Open and Enclosed Motors ................................................................55
1.3.12 Housed and Frameless Motors ...........................................................55
vii
viii Contents
1.3.13 Internal Rotor Motor and External Rotor Motor ................................56
1.3.14 Specialty Electric Motors ...................................................................56
1.3.14.1 Explosion Proof Motor and Flame Proof Motor .................57
1.3.14.2 S ubmersible Motor ..............................................................57
1.3.14.3 U ltrahigh-Speed Motor .......................................................58
1.3.14.4 Motor Operating under Vacuum Environment ...................60
1.3.14.5 Motor Operating under Nuclear Radiation Environment ...60
1.3.14.6 P iezoelectric Motor .............................................................61
1.3.15 Motor Classification According to Power Rating...............................63
1.4 Motor Design and Operation Parameters ........................................................65
1.4.1 Back EMF Constant, K .....................................................................65
e
1.4.2 T orque Constant, K ............................................................................65
t
1.4.3 V elocity Constant, K ..........................................................................66
v
1.4.4 M otor Constant, K ............................................................................67
m
1.4.5 Mechanical Time Constant, τ ...........................................................68
m
1.4.6 Electrical Time Constant, τ ...............................................................70
e
1.4.7 Thermal Time Constant, τ ................................................................70
th
1.4.8 V iscous Damping, K ........................................................................71
vd
1.5 Sizing Equations ..............................................................................................72
1.6 Motor Design Process and Considerations ......................................................73
1.6.1 Design Process ...................................................................................74
1.6.2 D esign Integration ..............................................................................81
1.6.3 M echatronics ......................................................................................82
1.6.4 Temperature Effect on Motor Performance .......................................83
1.7 M otor Failure Modes .......................................................................................85
1.8 I P Code ............................................................................................................86
References ..................................................................................................................88
Chapter 2 Rotor Design ...............................................................................................................95
2.1 Rotor in Induction Motor .................................................................................95
2.1.1 W ound Rotor ......................................................................................95
2.1.2 Squirrel Cage Rotor ............................................................................97
2.1.2.1 Factors Affecting Resistance of Squirrel Cage Rotor ........97
2.1.2.2 Double-Cage Rotor .............................................................98
2.1.2.3 Casting Squirrel Cage Rotor .............................................100
2.1.2.4 Skin Effect ........................................................................101
2.1.3 Induction Motor Design Types and Their Performing
Characteristics ..................................................................................102
2.2 P ermanent Magnet Rotor ...............................................................................103
2.2.1 Discovery of Phenomenon of Magnetism ........................................103
2.2.2 P ermanent Magnet Characteristics ..................................................103
2.2.3 Permanent Magnet Materials ...........................................................106
2.2.3.1 F errite Permanent Magnets ..............................................107
2.2.3.2 Rare Earth Permanent Magnets ........................................107
2.2.3.3 New Developments of Alternative PMs and
Reductions of Reliance on Rare Earths ............................109
2.2.4 M agnetization ...................................................................................112
2.2.5 Factors Causing Demagnetization ....................................................114
2.2.6 Maximum Operating Temperature ..................................................117
2.2.7 Permanent Magnet Mounting and Retention Methods ....................117
Contents ix
2.2.8 R ing Magnets ...................................................................................126
2.2.9 C orrosion Protection of Permanent Magnets ...................................129
2.3 R otor Manufacturing Process ........................................................................130
2.3.1 Lamination Materials .......................................................................130
2.3.2 Lamination Cutting ..........................................................................133
2.3.3 Lamination Surface Insulation .........................................................133
2.3.4 Lamination Annealing .....................................................................134
2.3.5 Lamination Stacking ........................................................................135
2.3.6 Rotor Casting for Squirrel Cage Motor ............................................135
2.3.7 Heat Treatment of Casted Rotor .......................................................136
2.3.8 R otor Assembly ................................................................................136
2.3.9 Rotor Machining and Runout Measurement ....................................136
2.3.10 R otor Balancing ................................................................................138
2.3.10.1 T ype of Unbalance ............................................................139
2.3.10.2 R otor Balancing Machine .................................................141
2.3.10.3 B alancing Operation .........................................................141
2.4 Interference Fit ..............................................................................................143
2.4.1 P ress Fit ............................................................................................144
2.4.2 Shrink Fit ..........................................................................................148
2.4.3 S erration Fit ......................................................................................151
2.4.4 F it with Knurling ..............................................................................151
2.4.5 Fit with Adjustable Ringfeder® Locking Devices ............................153
2.4.6 Fit with Tolerance Rings ..................................................................154
2.5 Stress Analysis of Rotor ................................................................................155
2.6 Rotordynamic Analysis .................................................................................157
2.6.1 R otor Inertia .....................................................................................159
2.6.2 Motor Critical Speed and Resonance ...............................................160
2.7 Rotor Burst Containment Analysis ................................................................164
2.7.1 Rotor Burst Speed ............................................................................164
2.7.2 Energy in Rotating Rotor .................................................................166
2.7.2.1 K inetic Energy in Rotor ....................................................166
2.7.2.2 Elastic Potential Energy in Rotor .....................................166
2.7.2.3 Ratio of Potential Energy to Kinetic Energy of Rotor ......167
2.7.3 Rotor Burst Containment Design .....................................................167
References ................................................................................................................169
Chapter 3 Shaft Design .............................................................................................................175
3.1 Shaft Materials ..............................................................................................175
3.2 S haft Loads ....................................................................................................178
3.3 Solid and Hollow Shafts ................................................................................180
3.4 Shaft Design Methods ...................................................................................180
3.4.1 M acaulay’s Method ..........................................................................180
3.4.2 Area–Moment Method .....................................................................181
3.4.3 C astigliano’s Method ........................................................................182
3.4.4 G raphical Method ............................................................................183
3.5 E ngineering Calculations ..............................................................................183
3.5.1 Normal Stress for Shaft Subjected to Axial Force ...........................183
3.5.2 Bending Stress for Shaft Subjected to Bending Moment .................185
3.5.3 Torsional Shear Stress and Torsional Deflection ..............................187
3.5.4 Lateral Deflection of Shaft ...............................................................192
x Contents
3.5.4.1 Lateral Deflection due to Bending Moment .....................192
3.5.4.2 Lateral Deflection due to Transverse Force ......................193
3.5.4.3 Lateral Deflection due to Shear Force ..............................195
3.6 Shaft Design Issues........................................................................................195
3.6.1 Shaft Design Considerations ............................................................195
3.6.2 Shaft Rigidity ...................................................................................197
3.6.3 Critical Shaft Speed .........................................................................197
3.6.3.1 Shaft with Uniform Diameter ...........................................198
3.6.3.2 Stepped Shaft ....................................................................198
3.6.4 Dimensional Tolerance .....................................................................198
3.6.5 Shaft Runout .....................................................................................198
3.6.6 Shaft Eccentricity .............................................................................200
3.6.7 Heat Treatment and Shaft Hardness .................................................200
3.6.8 Shaft Surface Finishing ....................................................................201
3.6.9 Shaft Lead ........................................................................................203
3.6.10 Shaft Seal .........................................................................................204
3.6.10.1 O-Ring Seal ......................................................................205
3.6.10.2 Universal Lip Seal ............................................................207
3.6.10.3 V-Shaped Spring Seal .......................................................207
3.6.10.4 Brush Seal .........................................................................208
3.6.10.5 PTFE Seal .........................................................................209
3.6.10.6 Spring-Energized Seal ......................................................210
3.6.10.7 Noncontact Seal ................................................................212
3.6.11 Diametrical Fit Types .......................................................................213
3.7 Stress Concentration ......................................................................................213
3.8 Torque Transmission through Mechanical Joints ..........................................214
3.8.1 Keyed Shafts.....................................................................................214
3.8.1.1 Selection of Key Material .................................................214
3.8.1.2 Stress Analysis of Key and Keyseat .................................214
3.8.1.3 Key Fit ..............................................................................218
3.8.1.4 Stress Concentration Factors of Keyed Shafts ..................218
3.8.2 Spline Shafts .....................................................................................220
3.8.2.1 Advantages of Spline Shafts .............................................221
3.8.2.2 Type of Spline ...................................................................221
3.8.2.3 Stress Concentration Factors of Spline Shafts ..................222
3.8.3 Tapered Shafts ..................................................................................222
3.9 Fatigue Failure under Alternative Loading ...................................................224
3.10 Shaft Manufacturing Methods ......................................................................224
3.10.1 Machined Shaft ................................................................................225
3.10.2 Forged Shaft .....................................................................................225
3.10.3 Welded Hollow Shaft .......................................................................226
3.10.4 Shaft Measurement ...........................................................................228
3.11 Shaft Misalignment between Motor and Driven Machine ............................228
3.11.1 Type of Misalignment ......................................................................229
3.11.2 Correction of Shaft Misalignment ...................................................230
3.12 Shaft Coupling ...............................................................................................231
3.12.1 Rigid and Semirigid Couplings ........................................................231
3.12.2 Flexible Couplings ............................................................................232
3.12.3 Non-Contact Couplings ....................................................................234
3.12.4 Oil Shear Couplings .........................................................................238
References ................................................................................................................239