industrial electricity controls

Industrial Electricity

&

Motor Controls

REX MILLER Professor Emeritus

State University College at Buffalo

MARK R. MILLER Professor

University of Texas at Tyler

Mc Graw Hill

New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan

Seoul Singapore Sydney Toronto

Contents с

Preface xiii

Introduction Performance Objectives 2 What Is Electricity? 2 Elements and Atoms 2

Free Electrons 3 Current Flow 3 Energy 3

Electrical Materials 3 Conductors 3 Insulators 3 Semiconductors 3

Generating Electricity 3 Voltage and Current 6

Resistance 8 Wire Size 9 Copper versus Aluminum Wire Circuits 9

Ohm's Law 12 Using Ohm's Law 12

Power 13 Kilowatts 13

Measuring Electricity 13 Meters 13 Other Types of Meters 19

Controlling Electricity 20 Switches 20 Solenoids 23 Relays 25 Diodes 25

Resistors 25 Resistor Color Code 27

Review Questions 27

1 Tools and Equipment Performance Objectives Hand Tools 30

Screwdrivers 30

30

Pliers 31 Hammers 32 Hacksaws 33 Wrenches 33 Nut Drivers 35 Tools for Bearings and

Bushings 35 Solder-Less Connector Crimper 36

Soldering Iron 36 Soldering Gun 36

Wire Gages 36 Fuse Puller 36 Tachometer 37 Knockout Punch 37 Fish Tape 37 Cable Stripper 37 Cable Cutter 38 Electrician's Knives 38 Other Tools 38

Electrical Tools 38 Portable Ammeter and Voltmeter Megohmmeter 39 Voltage Tester 39 Volt-Ohm-Milliammeter (VOM) Digital Logic Probe 40 Continuity Tester 40 Polarized Plug Tester 40 Recorder 42 Oscilloscope 42 Phase Sequence Adapter 43 Balance Analyzer 43

Special Tools for Specific Jobs 43 Printed Circuit Board Puller 43 Wire Wrap/Unwrap Tool 44 Conduit Benders 44 PVC Cutters 44 Cable Benders 45 Conduit Reamer 45

Review Questions 45 Review Problems 45

2 Safety in the Workplace Performance Objectives 48 Electrical Shock 48 Electrical Safety Measures 48

Using Ground-Fault Circuit Interrupters 48 Safety Devices 49 Circuit Protection 49 Over currents 49 Overloads 49 Short Circuits 50 Fuses 50

Electrical Codes 51 National Electrical Codes 51 Underwriters Laboratories 51 Canadian Standards Association 52 Standards in Other Countries 52

OSHA 53 Equipment Standards 53 OSHA Color Code 53

Fire Extinguishers 53 Safe Working Practices 53 Tool Safety 53

Using Hammers Properly 56 Working Clothes 56 Disconnects 56 Using Motors and Generators Safely 57 Grounding 58


3 Symbols Performance Objectives 62 Electrical Symbols 62

Common Switch (Button) Symbols 62 Standard Wiring Diagram Symbols 62

Electronic Symbols 62 Resistor Color Code 62 Electronic Symbols Compared 62

Relay Contact Symbols 62 Line Diagrams, Wiring Diagrams, and Ladder

Diagrams 62 Review Questions 66 Review Problems 70

4 Control Circuits and Diagrams Performance Objectives 72 Wiring Diagrams 72

Start Circuits 72 Line Diagram or Ladder Diagram 74 Undervoltage Release 74 Two-Wire Control Circuits 74 Thermostat Control 75 Undervoltage Protection 76

Three-Wire Control Circuits 76 Overcurrent Protection for Control

Circuits 78 Transformers in Control Circuits 79 Review Questions 81 Review Problems 81

S Switches Performance Objectives 84 Controlling Electricity 84 Drum Switch 84

Easy Conversion 85 Three-Phase Switching 85 DC Switching 86

Float Switches 86 Flow Switches 86 Foot Switches 89 Joystick 90 Interlock Switches 90

Mechanical Interlocking 90 Pushbutton Interlocking 91 Auxiliary Contact Interlocking 92

Limit Switches 93 Types of Limit Switches 93 Limit Switch Circuits 96

Pressure Switches 96 Pushbutton Switches 97 Safety Switches 98 Selector Switches 99 Single-Pole Switches 100 Start-Stop Switches 100 Temperature Switches 100 Toggle Switches 100 Transistor Switching 100 Vacuum Switches 102 Review Questions 102 Review Problems 102

A Magnetism and Solenoids Performance Objectives 106 Solenoids 106

Solenoid Valves 107 Automatic Gas Furnace Solenoid 108

Construction of Solenoids 108 Eddy Currents in the Armature

and Core 108 Air Gap and the Armature 108

Shading Coils 109 Solenoid Coils 109

Sealed Current Rating 110 Coil Voltage 110 Effects of Voltage Variation 110

Alternating Current Hum 111 Review Questions 111 Review Problems 112

vi Contents

7 Relays

117

Performance Objectives 114 Relays 114

Relay Solenoids 114 Uses for Relays 114 Relay Armature 114 Relay Contacts 115

Solid-State Relays 115 Transistor 115 Surge Protection 116 Triacs 116 Silicon-Controlled Rectifiers

Phase-Failure Relays 119 Solid-State Monitoring Relays 121

Voltage Relay 121 Current Relay 121 Over/Under Relay 122

Types of Solid-State Relay Switching 122

Switching Relay Loads 122 Thermistor Relay 123 Contact Amplifier Relay 123 Load Detector and Load Converter

Relays 123 Typical Applications 124

Thermal Overload Relays 125 Types of Thermal Overload Relays 125 Hand-Reset Melting Alloy

(NEMA Style) 126 Bimetallic Overloads (NEMA Style) 126 Temperature Compensation 126

Electromagnetic Relays and Motors 128 Motor Winding Relays 129

Electromechanical Relays 130 Relay Operating Characteristics 131

Contact Life 131 Contact Construction 131 Relay Coils 132 Shock and Vibration 132 Relays and Altitude 132


8 Electric Motors Performance Objectives 136 Motor Classifications 136 DC Motors 136

Operating Principles 136 Counter Electromotive Force Loads 137 Types of DC Motors 138 Series DC Motors 138 Shunt DC Motors 138 Compound DC Motors 139 Types of Armatures 139

137

Direction of Rotation 139 Motor Speed 139 Armature Reaction 140 Compensating Windings and Interpoles 140 DC Motor Starting Resistance 141 DC Motor Characteristics and Applications 141

Troubleshooting DC Motors 141 AC Motors 142

Types of AC Motors 142 Series AC Motor 142 Magnetic Fields in AC Motors 142 Rotating Magnetic Field: Two-Phase 143 Two-Phase Waveforms 143 Rotating Magnetic Field: Three-Phase 144 Synchronous Motors 144 Squirrel-Cage Motor 145 Starting the Synchronous Motor 145 Induction Motors 146 Stator Construction 146 Slip 147 Single-Phase Induction Motors 148 Split-Phase Induction Types 148 Shaded-Pole Induction Motors 149 Speed and Slip in Squirrel-Cage Motors 150 Rotation 150 Torque and Horsepower 151 Locked-Rotor Torque 151 Breakdown Torque 151 Locked-Rotor kVA/hp 152 Starting Squirrel-Cage Motors 152


Q Timers and Sensors Performance Objectives 156 Time and Timers 156 Dashpot or Pneumatic Time-Delay

Timers 156 Synchronous Clock Timers 156 Solid-State Timers 156 Time-Delay Relays 157 General Purpose Timing Relays 158 Control of Programmable Timers 158 Digital Solid-State Timer/Counter 159

Single-Stage Version 159 Time/Count Modes 159 Dual-Stage Version 159 Thumbwheel Switches 160

DIP Switches 161 Pneumatic Timing Relays 161 Motor-Driven Timers 163 Sequence Control 164 Programmable Timers 165 Sensors 165

Contents vii

Solid State Level Controls 165 Capacitance-Туре Sensor 166 Temperature Sensing 166 Thermocouple 167 Thermistor 167 Resistance Temperature Devices 167 Semiconductor Temperature Sensor 169 Pressure Sensors 169 Strain Gage Transducers 169 Piezo-resistive Transducers 169


JO Sensors and Sensing Performance Objectives 172 Classes of Sensors 172

Contact Sensors 172 Noncontact Sensors 172

Presence Sensing 172 Limit Switches 172 Speed Switches 174

Operation of the Speed Switch 175 Pressure Controls 176 Temperature Controls 177

Wells and Packing Glands 177 Float Switches 179 Encoders 179

Optical Programmable Controller Encoders 179

Multiplexing 182 Proximity Switches 182

Operation 182 Solid-State Switches 182 Inductive Cylindrical Switch 182 Extended-Sensing-Range Inductive

Proximity Switch 183 Compact Inductive Proximity

Switch 183 Self-Contained Low Profile Proximity

Switch 183 Photoelectric Switches 183

Operation 184 Features 184 Photoelectric Light Sources 185 Mark Sensors 185 Clear Material Detection 186

Switch Applications 186 Automatic Identification 186 Radio-Frequency Identification

Systems 187 The Antenna 188 The RF Tag 188

Bar Code Readers and Decoders 188 Hand-Held Scanners 189 Moving-Beam Scanners 189

Multiplexing 189 Vision System 189 Review Questions 190

1 J Solenoids and Valves Performance Objectives 192 Solenoids 192 Industrial Solenoids 192

Tubular Solenoids 192 Frame Solenoids 192

Applications 195 Solenoids as Electromagnets 195 Solenoid Coils 195 Servicing Coils 196

Solenoid Valves in Circuits 196 Refrigeration Valve 197

Review Questions 198

\2 Motor Starting Methods Performance Objectives 200 Electric Motors 200 Starting the Motor 200

Reversibility 201 Uses 201

Repulsion-Induction Motor 201 Uses 202

Capacitor-Start Motor 202 Reversibility 202

Uses 203 Permanent Split-Capacitor Motor 204 Shaded-Pole Motor 204

Reversibility 205 Uses 205

Split-Phase Motor 205 Polyphase Motor Starters 206 Reduced-Voltage Starting Methods 206 Primary Resistor Starting 208

Operation 209 Autotransformer Starting 209

Operation 210 Part-Winding Starting 211

Operation 212 Advantages and Disadvantages 212

Wye-Delta or Star-Delta Starters 212 Operation 213 Advantages and Disadvantages 213 Star-Delta (Wye-Delta) Connections 213

Multispeed Starters 214 Low-Speed Compelling Relay 214 Automatic Sequence Accelerating

Relay 214 Automatic Sequence Decelerating Relay 214

viii Contents

Consequent-Pole Motor Controller 215 Full-Voltage Controllers 217 Starting Sequence 217 Protection against Low Voltage 218 Time-Delay Protection 218 Review Questions 221

1 3 Solid-State Reduced-Voltage Starters Performance Objectives 224 Electromechanical Devices 224 Reduced-Voltage Starting 224 Silicon-Controlled Rectifiers 224 Solid-State Stepless Acceleration 226 Logic Rack 226

B-2 Module 226 B-3 Module 226 B-4 Module 227 B-5 Module 228 B-6 Module 228 B-7 Voltage Monitor Module 228 B-8 Energy-Saving Module 228

Shorted SCR Switch 228 Elementary Wiring Diagrams for

Solid State 228 Diac 229 Triac 230 Light-Emitting Diodes 231 Using Solid-State Control and Electromagnetic Devices 231

Surge Suppressors 231 Lightning Protection 232 Review Questions 232

| 4 Speed Control and Monitoring Performance Objectives 234 Motor Speed Control 234 Squirrel-Cage Motors 234 Synchronous Motors 234

Excitation 235 Speed 235 Starting 236 Starting Methods 236 Uses for Synchronous Motors 238

Wound-Rotor Motors 238 Speed Regulation by Resistance 238 Types of Speed Control 239 Multiswitch Starters 239 Dram Controllers 240 Magnetic Starters 240 Resistors 240 Solid-State Adjustable-Speed Controllers 241

Frequency Speed Control 241

15

Multispeed Starters 242 Speed Monitoring 242 Review Questions 243

Motor Control and Protection Performance Objectives 246 Motor Control 246 Manual Starters 246 Solid-State Motor Controller 248 Sequence Control 249 When Starting any One Requires

Another 250 Automatic Sequence Control 250

Jogging 252 Forward or Reverse Jogging 253

Plugging 254 Plugging a Motor to Stop from Either Direction 254

Antiplugging 254 Braking 255

Electronic Motor Brake 255 Mechanical Braking 257 Thraster Brakes 258 Magnetic Brakes 258 Hydraulic Brakes 259

Motor Protection 259 Surge Protection and Backspin 259 Overload Protection 260 Automatic Reset Overload Relay 260 Inverse Time Current Relay 261 Solid-State, Line-Voltage and Line-Current Monitor Relays 261

Programmable Motor Protection 262 Protective Module 262 Remote Temperature Detector Module 262


| £ Three-Phase Controllers Performance Objectives 266 The Three-Phase Motor 266 Starters 266

Simplest Type 266 Full-Voltage Reversing Starter 267 Forward-Reverse-Stop 267 Start-Stop Jog 267 Reversing Starter 268 Two-Speed Starter 268

Duplex Motor Controllers 269 Medium-Voltage Controllers 269 Solid-State Motor Controller 274

Modules 275 Solid-State Advantages 275

Motor Control Centers 275 Review Questions 276

Contents lx

2 7 Drives Performance Objectives 278 Fans, Blowers, and Pumps 278 Adjustable-Speed Drives 278 Adjustable-Frequency AC Drives 278 CSI Inverters 279 Variable-Voltage Inverters 279 Pulse-Width-Modulated Inverters 280 Variable-Pitch Drives 281 Wound-Rotor AC Motor Drives 282 DC Drives 282 Regulated Speed Drives 282 Open-Loop Controls (Traditional Approach) 282

Closed-Loop Controls 284 DC Drives: Advantages and Disadvantages 284

DC Drives and Systems 284 Solid-State Digital AC Drives 285 Review Questions 286

2 g Transformers Performance Objectives 288 Transformers 288 Iron-Core Transformer 288

Turns Ratio 288 Autotransformers 289

Turns Ratio 289 Transformer Losses 289

Eddy Current Losses 289 Hysteresis Losses 290 Copper Losses 290

Core Construction 290 Transformer Oil 291

EPA Highlights 292 Autotransformers: Three- and Single-Phase 292

Impedances 293 Third Harmonics 293 Grounding 294

Buck and Boost Transformers 294 Calculating the Load 294 Calculating Single-Phase

Kilovolt-Amperes 295 Three-Phase Buck and Boost

Transformers 296 Calculating Three-Phase

Kilovolt-Amperes 296 Dry-Type Transformers 296

Cooling 297 Insulation and Temperature

Rise 297 Taps 297

Special Transformers 297

Liquid-Filled Transformers 299 Safety Notice 299

Submersible Transformer 299 Maintenance 299

Transformer Applications 301 Distributing Power at High

Voltages 301 Double-Wiring Elimination 301 Operating 120/240-V Equipment from Power Circuits 301

Isolating Circuits 302 Changing from a Four-Wire to Three-Wire

Circuit 302 Stepping-Up or Stepping-Down Voltage 302

Motor Transformers 302 Review Questions 306 Review Problems 306

J 9 Power Generation, Performance Objectives 308 Basic Principle 308

Sine Wave 309 Components of the Alternator 309

Rotors 309 Stators 309 Exciters 310

Types of Alternators 311 Single-Phase 311 Two-Phase 311 Three-Phase 312

Wye and Delta Configurations 312 Wye Connection 312 Delta Connection 312 Power in a Balanced Wye 313 Power in a Balanced Delta 313

Frequency 313 Load Changes 314

Armature Resistance 314 Armature Reactance 314 Armature Reaction 314

Voltage Regulation 314 Standby or Emergency Power Sources 314

Transfer Switch 314 Types of Standby Generators 315 Automatic Transfer Switches 316 Electronic Loads 317 Uninterruptible Power Systems 317 Multiple-Engine Generator Sets 317 Systems for Paralleling Multiple Power Sources 318

Selective Load Transfer Systems 318 Prime Mover Systems 319

Two-Source Systems 319 Multiple-Source Systems 319

X Contents

Power Management Systems 320 Peak Load-Sharing Systems 320 Utility-Isolated Peaking Transfer

System 320 Utility-Paralleled Peaking

Systems 321 Review Questions 321 Review Problems 322

2 0 Power Distribution Systems Performance Objectives 324 Sources of Commercial AC 324

Falling-Water Generators 324 Switchyard 325 Nuclear Power Generators 325 Fossil-Fuel Power Generators 325

Distribution 328 Types of Distribution Systems 328

Systems Analysis 333 Short-Circuit Currents 334 Fault Currents 334 Three-Phase Power 334

Measurement of Power 335 Transformers 336

Transformer Construction 336 Three-Phase Transformer

Connections 337 Switching 341

Automatic Emergency Power Switching 342

Switchboards 344 Panel Boards 345 Raceways 345 Aluminum Lay-In Wall Duct and

Floor Trench Duct 346 Cable Tray 346


2 J Programmable Controllers Performance Objectives 352

NEMA PLC Definition 352 Solid-State Electronics 352

Standard Electronic Features in Controls 352

The Programmable Controller 353 Input-Output 353 Interfacing 353 ASCII Code 353 Parallel Ports 354 Serial Ports 354

The Environment Affects Performance 354

Electrical Noise 354 Installation Practices 355 Grounding 355

Solid-State Reliability 355 Backup Operations 355

Controllers 356 System Hardware and Programming Equipment 356

Processors 356 Input-Output Modules 358 Intelligent I/O Modules 358 Display Systems 359 Cell Controllers 360 Micro-Cell Controller 360 Local Area Network 361 Future of PLCs 361


Troubleshooting and Maintenance Performance Objectives 366 Troubleshooting and the Electrician 366 Preventive Maintenance 366

Damp and Wet Areas 366 Prevention of Accidental Shock 367 Ground-Fault Receptacles 367 Wiring Devices 367

Maintenance of Small Electric Motors 370 Adequate Wiring 370 Check Internal Switches 370 Check Load Condition 370 Extra Care in Lubrication 370 Keep Commutators Clean 370 Motors Must Have Proper Service

Rating 370 Replace Worn Brushes 370

Motor Problems 370 Ball Bearing Motors 370 Sleeve Bearing Motors 371

Common Motor Problems and Their Causes 371

Problem Diagnosis 372 Centrifugal Switches 372 Commutator-Type Motors 372

Troubleshooting Aids 372 Connection Diagrams 372 Small Three-Phase Motor Rating Data 372

Power Supply Disturbances 375 Voltage Fluctuations 376 Transients 376 Power Outages 377 Looking for Shorts 377

Motors with Squirrel-Cage Rotors 377 Testing the Centrifugal Switch in a

Single-Phase Motor 377

Contents xi

Testing for Short Circuits between Run and Start Windings 378

Capacitor Testing 378 Measuring Capacity of a Capacitor 378

Using Meters to Check for Problems 379 Using a Volt-Ammeter for Troubleshooting

Electric Motors 379 Clamp-On Volt-Ammeter 379 Looking for Grounds 380 Looking for Opens 380

Troubleshooting Guide 380 Motor Life 384

Ventilation 384 Ambient Temperature 384

Performance Characteristics 385 Voltage Unbalance 385

Motor Protection 386 DC Motor Problems 386 Solid-State Equipment

Troubleshooting 391 Review Questions 391

2 3 Careers in Electricity Performance Objectives 394

Industrial Electrician 394 Industries That Employ Electricians 394 Careers in Electricity 394

Electrical Engineer 395 Construction Electrician 395 Maintenance Electrician 396 Limited Energy Electrician 396

General Information 396 Information Sources 397

Starting Your Own Business 397 The Development of Leadership 398

Employment of Electricians 398 Earnings 398 Related Occupations 398 Sources of Additional Information 399

Glossary

Appendices I. DC Motor Trouble Chart 405

II. Wound-Rotor Motor Trouble Chart 407

III. Fractional-Horsepower Motor Trouble Chart 409

IV. Selection of Dual-Element Fuses for Motor-Running Overload Protection 415

V. Tables and Formulas 417 VI. Full-Load Currents of AC and

DC Motors 423 VII. Power Factor Correcting

Capacitors 425 VIII. Switch Symbols 429

IX. Wiring Diagram Symbols 431 X. Unit Prefixes 433

XL Conversion Factors 435 XII. Decibel Table 437

Index 439

industrial electricity controls

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