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Electric Motor Repair Handbook

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Electric Motor Repair and Use Handbook

John E. Traister

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Open: Electric Motor Repair and Use Handbook

Everyone associated in any capacity with the electrical industry will deal to some degree with electric motors and generators, as the electric motor is the principal means of changing electrical energy into mechanical energy to power all types of appliances and machines.

Most publications of the past have dealt quite heavily on theory and underlying principles, while brushing very lightly over the essential applications of electric motors. This publication does not slight the importance of certain principles that make possible the operation of rotary machinery, but more emphasis is placed on practical application of electric motors-the selection, use, and repair of them.

This book is not designed to be a “crash course” on electrical motor repair. Rather, it is meant to cover the entire field of motor applications, from the various available motor types to their use and repair. It cannot take the place of experience, but it can give the reader a very sound foundation upon which to build. The book should also prove useful to the experienced electrician or engineer as a review of motor applications.

Industrial electric shops will want to keep a copy of this book handy at all times for daily reference, and design and engineering departments will find constant use for the book in selecting motors for various applications, including machine design

Over the past decade or so, many motor users have stopped doing their own repairs and have all work done by a qualified motor-repair shop. However, many of these same plants are now reconsidering the organization of their own in-house motor-repair shops to ensure prompt repair of motors that operate critical machines. This book should be extremely important to plants and personnel in this category.

A deep and grateful bow must be made in the direction of all manufacturers and others in the electrical industry who supplied helpful reference material and photos. This book could not have been completed without them. Credit lines appear throughout the book in their appropriate places, and names and addresses also appear in the appendix should the reader wish to contact them directly for further information on their products.

I am also indebted to Ros Herion of Prentice-Hall, who did the production work on this book. Her gentle (and sometimes hard) prodding kept the book moving along so that it could be published on time . . . and my wounds have just about healed by now. (Editor's note: Although a minimum of tongue-lashing was necessary, no whiplashing was required or employed.)

PREFACE xi

1 INTRODUCTION TO ELECTRIC MOTORS 1
Magnetism 2
Electromagnetic Induction 3
Power and Energy 6
Basic Electric Motor Principles 7
Basic Motor Terms and Nameplate Information 8
Bearings Terms 11
Mounting Terms 11

2 SPLIT-PHASE MOTORS 12
Centrifugal Switch 13
Squirrel-Cage Rotor 14
Split-Phase Motor Troubles 15

3 CAPACITOR MOTORS 19
Capacitors 21
4 REPULSION-TYPE MOTORS 23
Repulsion-Start, Induction-Run Motors 23
Repulsion Motors 24
Repulsion-Start-Induction Motors 25
Motor Drives 2

5 POLYPHASE MOTORS 27
Operating Principles of Two-Phase Motors 29
Operating Principles of Three-Phase Motors 32
Polyphase Motor Enclosures 34
Motor Type 36
Synchronous Motors 37

6 ALTERNATING-CURRENT MOTOR CONTROL 38
Manual Starter 39
Magnetic Motor Controllers 40
Overload Protection 43
Protective Enclosures 51
National Electrical Code Requirements 53
Control Circuits 53
Other Controlling Equipment 59
Electronic Controls 60
Energy Management Systems 61
Programmable Controllers 62

7 DIRECT-CURRENT ARMATURE WINDINGS 63
Lap Windings and Wave Windings 63
Armature Equalizer Connections 69
Winding Small Armatures 71

8 DIRECT-CURRENT MOTORS 74
dc Motor Construction 75
Brushless dc Motors 81
Motor Braking 82
Dynamic Braking 83

9 DIRECT-CURRENT MOTOR CONTROL 84
dc Controllers 84 Variable-Voltage Control 92
Overload Relays 93

10 UNIVERSAL, SHADED POLE, AND FAN MOTORS 95
Universal Motors 95
Shaded Pole Motor 96
Distributed-Field Compensated Motor 97
Reversing Shaded Pole Motors 98

11 GENERATORS 99
Direct-Current Generators 99
Cycles and Alternations 103
Frequency 104
Alternators 104
Single-Phase Systems 105
Two-Phase Systems 106
Three-Phase Systems 107

12 SELECTION OF ELECTRIC MOTORS FOR THE JOB 110
Types of Drives 110
Selecting the Motor for the Job 112
Power Supply 113
Load Factor 113
Types of Mounting and Enclosures 114
High-Speed Belting 115
Duty Cycle 116
Inertia 118
Shock Load 119
Radiation 120
Temperature 121
Corrosion 121
Acknowledgments 123

13 MOTOR INSTALLATION 124
Uncrating 124
Safety 125
Thermal Protector Information 125
Location 126
Motor Drives 127
Electrical Connections 128
Changing Rotation 129
Part Winding Starting 129
Operation 129

14 MAINTENANCE OF ELECTRIC MOTORS 132
Cleanliness 132
Lubrication 132
Practical Maintenance Techniques 133

15 TROUBLESHOOTING AC MOTORS Grounded Coils 142
Shorted Coil 143
Open Coils 144
Reversed Connections 145
Reversed Phase 146
Troubleshooting Split-Phase Motors 149

16 TROUBLESHOOTING DC MOTORS Ground Test 152
Test for Opens 152
Armature Testing 154
Reversed Coil 159
Grounded Coils 159
Shorts Between Coils 159
Reversed Loops 159
Shorted Commutator Segments 160
Grounded Commutator Segments 160
Galvanometer Tests on Armatures 160
Removing Faulty Coils 162
Constructing Growlers 163

17 TESTING AND MEASURING INSTRUMENTS
Volt-Ohm-Ammeter 165
Megger® Tester Applications 169
Growler for Testing Armatures 171
Special Testers 172
Insulation Breakdown Tester UHZ 173
Testing of Step Motors 174
Tachometer 181

18 TOOLS FOR MOTOR REPAIR THUMM
Machines 184
Abisofix Isolex 191
Metal Turning Lathe 192
Motor Repair Materials 193
19 MOTOR REPAIR Collecting Data 195
Lead Connections 199
Recording Data 200
Data Cards 201

20 MOTOR REPAIR TECHNIQUES 203
Commutators 204
Removing Insulation 205
Coil and Slot Insulation 206

21 AC MOTOR WINDINGS 210
Spiral-Type, Lap, and Wave Windings 210
Coil Polarity 212
Types of Coils 213
Winding Faults 214 22

MOTOR WINDING 215
Motor Winding 216
Form-Wound Armatures 219
Winding Stators 221

23 REWINDING AND RECONNECTING 224
Change of Phases and Frequency 226
Changing Number of Poles and Speed 226
Completing the Winding Job 227
Soldering Leads 230
Baking and Varnishing 230

APPENDIX: TRADE SOURCES 233
Motors and Motor Controls 233
Testing and Measuring Devices (Instruments) 234
INDEX 25