Contents
1 Rotating Machine Insulation Systems 1
1.1 Types of Rotating Machines 1
1.1.1 AC Motors 2
1.1.2 Synchronous Generators 4
1.1.3 Classification by Cooling 6
1.2 Purpose of Windings 7
1.2.1 Stator Winding 7
1.2.2 Insulated Rotor Windings 9
1.2.3 Squirrel Cage Induction Motor Rotor Windings 9
1.3 Types of Stator Winding Construction 9
1.3.1 Random-Wound Stators 10
1.3.2 Form-Wound Stators—Coil Type 10
1.3.3 Form-Wound Stators—Roebel Bar Type 12
1.4 Stator Winding Insulation System Features 12
1.4.1 Strand Insulation 12
1.4.2 Turn Insulation 17
1.4.3 Groundwall Insulation 18
1.4.4 Groundwall Partial Discharge Suppression 20
1.4.5 Groundwall Stress Relief Coatings 24
1.4.6 Mechanical Support in the Slot 27
1.4.7 Mechanical Support in the End-Winding 29
1.4.8 Transposition Insulation 31
1.5 Rotor Winding Insulation System Components 34
1.5.1 Salient Pole Rotor 35
1.5.2 Round Rotors 36
1.5.3 Induction Motor Wound Rotors 38
References 40
2 Evaluating Insulation Materials and Systems 43
2.1 Aging Stresses 44
2.1.1 Thermal Stress 45
2.1.2 Electric Stress 46
2.1.3 Ambient Stress (Factors) 47
2.1.4 Mechanical Stress 48
2.1.5 Multiple Stresses 49
2.2 Principles of Accelerated Aging Tests 49
2.2.1 Candidate and Reference Materials/Systems 50
2.2.2 Statistical Variation 50
2.2.3 Failure Indicators 55
2.3 Thermal Endurance Tests 56
2.3.1 Basic Principles 56
2.3.2 Thermal Identification and Classification 57
2.3.3 Insulating Material Thermal Aging Tests 58
2.3.4 Insulation Systems Thermal Aging Tests 58
2.3.5 Future Trends 60
2.4 Electrical Endurance Tests 60
2.4.1 Proprietary Tests for Form-Wound Coils 61
2.4.2 Standardized Test Methods for Form-Wound Coils 62
2.5 Thermal Cycling Tests 63
2.5.1 IEEE Thermal Cycling Test 63
2.5.2 IEC Thermal Cycling Test 64
2.6 Multifactor Stress Testing 65
2.7 Nuclear Environmental Qualification Tests 65
2.7.1 Environmental Qualification (EQ) by Testing 66
2.7.2 Environmental Qualification by Analysis 66
2.7.3 Environmental Qualification by a Combination 67
of Testing and Analysis
2.8 Material Property Tests 67
References 69
3 Historical Development of Insulation Materials and Systems 73
3.1 Natural Materials 74
3.2 Early Synthetics 76
3.3 Plastic Films and Nonwovens 78
3.4 Liquid Synthetic Resins 79
3.4.1 Polyesters 79
3.4.2 Epoxides (Epoxy Resins) 81
3.5 Mica 83
3.5.1 Mica Splittings 83
3.5.2 Mica Paper 84
3.6 Glass Fibers 86
3.7 Laminates 87
3.8 Evolution of Wire and Strand Insulation 88
3.9 Manufacture of Random-Wound Stator Coils 89
3.10 Manufacture of Form-Wound Coils and Bars 89
3.10.1 Early Systems 89
3.10.2 Asphaltic Mica Systems 90
3.10.3 Individual Coil and Bar Thermoset Systems 90
3.10.4 Global VPI Systems 91
3.11 Wire Transposition Insulation 92
3.12 Insulating Liners, Separators and Sleeving 93
3.12.1 Random-Wound Stators 93
3.12.2 Rotors 93
References 94
4 Stator Winding Insulation Systems in Current Use 95
4.1 Methods of Applying Form-Wound Stator Coil Insulation 97
4.2 Description of Major Trademarked Form-Wound Stator 99
4.2.1 Westinghouse Electric Co.:ThermalasticTM 99
4.2.2 General Electric Co.: Micapals I and IITM 100
4.2.3 Alsthom, GEC Alsthom, Alstom Power: Isotenax,TM 101
4.2.4 Siemens AG, KWU: MicalasticTM 102
4.2.5 ABB Industrie AG: MicadurTM, Micadur Compact,TM 102
4.2.6 Toshiba Corporation: Tosrich,TM Tostight ITM 103
4.2.7 Mitsubishi Electric Corporation 104
4.2.8 Hitachi Ltd.: HiResin,TM Hi-Mold,TM Super Hi-ResinTM 104
4.2.9 Summary of Present-Day Insulation Systems 104
4.3 Recent Developments for Form-Wound Insulation Systems 105
4.4 Random-Wound Stator Insulation Systems 107
4.4.1 Magnet Wire Insulation 107
4.4.2 Phase and Ground Insulation 108
4.4.3 Varnish Treatment and Impregnation 108
4.5 Revolutionary Stator Winding Insulation Systems 108
4.5.1 Superconducting Windings 108
4.5.2 PowerFormer™ 109
References 110
5 Rotor Winding Insulation Systems 113
5.1 Rotor Slot and Turn Insulation 114
5.2 Collector Insulation 115
5.3 End-Winding Insulation and Blocking 116
5.4 Retaining Ring Insulation 116
5.5 Direct-Cooled Rotor Insulation 117
6 Core Laminations and Their Insulation 119
6.1 Electromagnetic Materials 119
6.1.1 Magnetic Fields 119
6.1.2 Ferromagnetism 119
6.1.3 Magnetization Saturation Curve 120
6.1.4 Ferromagnetic Materials 120
6.1.5 Permeability 121
6.1.6 Hysteresis Loop 121
6.1.7 Eddy Current Loss 122
6.1.8 Other Factors Affecting Core Loss 122
6.1.9 Effect of Direction of the Grain 124
6.1.10 Effect of Temperature 124
6.1.11 Effect of Heat Treatment 124
6.1.12 Effect of Impurities and Alloying Elements 124
6.1.13 Silicon/Aluminum Steels 125
6.2 Mill-Applied Insulation 125
6.3 Lamination Punching and Laser Cutting 125
6.4 Annealing and Burr Removal 126
6.5 Enameling or Film Coatings 127
References 127
7 General Principles of Winding Failure, Repair and Rewinding 129
7.1 Failure Processes 129
7.1.1 Relative Failure Rates of Components 131
7.1.2 Factors Affecting Failure Mechanism Predominance 132
7.2 Factors Affecting Repair Decisions 133
7.3 Cutting Out Stator Coils After Failure 134
7.4 Rewinding 134
References 135
8 Stator Failure Mechanisms and Repair 137
8.1 Thermal Deterioration 137
8.1.1 General Process 137
8.1.2 Root Causes 139
8.1.3 Symptoms 140
8.1.4 Remedies 141
8.2 Thermal Cycling 141
8.2.1 General Process 142
8.2.2 Root Causes 144
8.2.3 Symptoms 145
8.2.4 Remedies 145
8.3 Inadequate Impregnation or Dipping 146
8.3.1 General Process 146
8.3.2 Root Causes 146
8.3.3 Symptoms 148
8.3.4 Remedies 148
8.4 Loose Coils in the Slot 148
8.4.1 General Process 148
8.4.2 Root Causes 149
8.4.3 Symptoms 151
8.4.4 Remedies 152
8.5 Semiconductive Coating Failure 152
8.5.1 General Process 152
8.5.2 Root Causes 153
8.5.3 Symptoms 153
8.5.4 Remedies 154
8.6 Semiconductive/Grading Coating Overlap Failure 155
8.6.1 General Process 155
8.6.2 Root Causes 156
8.6.3 Symptoms 156
8.6.4 Remedies 156
8.7 Repetitive Voltage Surges 157
8.7.1 General Process 158
8.7.2 Root Cause 159
8.7.3 Symptoms 160
8.7.4 Remedies 160
8.8 Contamination (Electrical Tracking) 161
8.8.1 General Process 161
8.8.2 Root Causes 164
8.8.3 Symptoms 164
8.8.4 Remedies 164
8.9 Abrasive Particles 165
8.9.1 General Process 165
8.9.2 Root Causes 165
8.9.3 Symptoms and Remedies 166
8.10 Chemical Attack 166
8.10.1 General Process 166
8.10.2 Root Causes 167
8.10.3 Symptoms 167
8.10.4 Remedies 167
8.11 Inadequate End-Winding Spacing 168
8.11.1 General Process 168
8.11.2 Root Causes 170
8.11.3 Symptoms 170
8.11.4 Remedies 171
8.12 End-Winding Vibration 172
8.12.1 General Process 172
8.12.2 Root Causes 173
8.12.3 Symptoms 174
8.12.4 Remedies 174
8.13 Stator Coolant Water Leaks 175
8.13.1 General Process 175
8.13.2 Root Causes 176
8.13.3 Symptoms 177
8.13.4 Remedies 177
8.14 Poor Electrical Connections 177
8.14.1 General Process 178
8.14.2 Root Causes 178
8.14.3 Symptoms 178
8.14.4 Remedies 179
References 179
9 Rotor Winding Failure Mechanisms and Repair 181
9.1 Round Rotor Windings 181
9.1.1 Thermal Deterioration 181
9.1.2 Thermal Cycling 183
9.1.3 Abrasion Due To Imbalance or Turning Gear Operation 186
9.1.4 Pollution (Tracking) 187
9.1.5 Repetitive Voltage Surges 188
9.1.6 Centrifugal Force 189
9.1.7 Remedies 191
9.2 Salient Pole Rotor Windings 192
9.2.1 Thermal Aging 192
9.2.2 Thermal Cycling 193
9.2.3 Pollution (Tracking and Moisture Absorption) 194
9.2.4 Abrasive Particles 195
9.2.5 Centrifugal Force 195
9.2.6 Repetitive Voltage Surges 196
9.2.7 Remedies 196
9.3 Wound Induction Rotor Windings 198
9.3.1 Transient Overvoltages 198
9.3.2 Unbalanced Stator Voltages 199
9.3.3 High-Resistance Connections—Bar Lap 199
9.3.4 End-Winding Banding Failures 200
9.3.5 Slip Ring Insulation Shorting and Grounding 200
9.3.6 Remedies 201
9.4 Squirrel Cage Induction Rotor Windings 202
9.4.1 Thermal 202
9.4.2 Cyclic Mechanical Stressing 203
9.4.3 Poor Design/Manufacture 206
9.4.4 Repairs 208
References 209
10 Core Lamination Insulation Failure and Repair 211
10.1 Thermal Deterioration 211
10.1.1 General Process 212
10.1.2 Root Causes 212
10.1.3 Common Symptoms 213
10.2 Electrical Degradation 214
10.2.1 General Process 214
10.2.2 Root Causes 214
10.2.3 Common Symptoms 217
10.3 Mechanical Degradation 218
10.3.1 General Process 218
10.3.2 Root Causes 218
10.3.3 Symptoms 221
10.4 Failures Due To Manufacturing Defects 221
10.4.1 General Process 221
10.4.2 Root Causes 222
10.4.3 Symptoms 222
10.5 Core Repairs 222
10.5.1 Loose Cores 223
10.5.2 Core Insulation Shorting 223
10.5.3 Core Damage Due to Winding Electrical Faults 224
10.5.4 False Tooth 225
10.5.5 Cracked Through-Bolt Insulation 225
References 225
11 General Principles of Testing and Monitoring 227
11.1 Purpose of Testing and Monitoring 227
11.1.1 Assessing Winding Condition and Remaining 227
11.1.2 Prioritizing Maintenance 228
11.1.3 Commissioning and Warranty Testing 228
11.1.4 Determining Root Cause of Failure 228
11.2 Off-Line Testing Versus On-Line Monitoring 229
11.3 Role of Visual Inspections 230
11.4 Expert Systems to Convert Data into Information 230
11.4.1 Off-Line Expert Systems 231
11.4.2 On-Line Expert Systems 231
References 233
12 Off-Line Rotor and Stator Winding Tests 235
12.1 Insulation Resistance and Polarization Index 235
12.1.1 Purpose and Theory 238
12.1.2 Test Method 240
12.1.3 Interpretation 241
12.2 DC Hipot 243
12.2.1 Purpose and Theory 243
12.2.2 Test Method 243
12.2.3 Interpretation 245
12.3 DC Conductivity Test 246
12.3.1 Purpose and Theory 246
12.3.2 Test Method 246
12.3.3 Interpretation 247
12.4 AC Hipot Test 247
12.4.1 Purpose and Theory 248
12.4.2 Test Method 249
12.4.3 Interpretation 249
12.5 Capacitance Test 249
12.5.1 Purpose and Theory 250
12.5.2 Test Method 250
12.5.3 Interpretation 251
12.6 Capacitance Tip-Up Test 252
12.6.1 Purpose and Theory 252
12.6.2 Test Method 253
12.6.3 Interpretation 253
12.7 Capacitive Impedance For Motor Stators 254
12.8 Dissipation (or Power) Factor Test 254
12.8.1 Purpose and Theory 255
12.8.2 Test Method 255
12.8.3 Interpretation 257
12.9 Power (Dissipation) Factor Tip-Up Test 257
12.9.1 Purpose and Theory 257
12.9.2 Test Method 258
12.9.3 Interpretation 259
12.10 Off-Line Partial Discharge Test 259
12.10.1 Purpose and Theory 259
12.10.2 Test Method 261
12.10.3 Interpretation 262
12.11 Partial Discharge Probe Tests 263
12.11.1 Purpose and Theory 263
12.11.2 Test Method 264
12.11.3 Interpretation 264
12.12 Stator Surge Comparison Test 265
12.12.1 Purpose and Theory 265
12.12.2 Test Method 267
12.12.3 Interpretation 267
12.13 Inductive Impedance Test 268
12.14 Semiconductive Coating Contact Resistance Test 269
12.14.1 Purpose and Theory 269
12.14.2 Test Method 269
12.14.3 Interpretation 270
12.15 Conductor Coolant Tube Resistance 270
12.15.1 Purpose and Test Method 270
12.16 Stator Wedge Tap Test 270
12.16.1 Purpose and Theory 271
12.16.2 Test Method 271
12.16.3 Interpretation 271
12.17 Slot Side Clearance Test 272
12.17.1 Purpose and Theory 272
12.17.2 Test Method 272
12.17.3 Interpretation 272
12.18 Stator Slot Radial Clearance Test 273
12.18.1 Purpose and Theory 273
12.18.2 Test Method 273
12.18.3 Interpretation 273
12.19 Stator End-Winding Resonance Test 273
12.19.1 Purpose and Theory 274
12.19.2 Test Method 274
12.19.3 Interpretation 274
12.20 Rotor Voltage Drop Test 274
12.20.1 Purpose and Theory 275
12.20.2 Test Method 275
12.20.3 Interpretation 275
12.21 Rotor RSO and Surge Test 275
12.21.1 Purpose and Theory 275
12.21.2 Test Method 276
12.21.3 Interpretation 276
12.22 Rotor Growler Test 277
12.22.1 Purpose and Theory 277
12.22.2 Test Method 277
12.22.3 Interpretation 278
12.23 Rotor Fluorescent Dye Penetrant 278
12.23.1 Purpose and Theory 278
12.23.2 Test Method and Interpretation 278
12.24 Rotor Rated Flux Test 278
12.24.1 Purpose and Theory 278
12.24.2 Test Method 278
12.24.3 Interpretation 279
12.25 Rotor Single-Phase Rotation Test 279
12.25.1 Purpose and Theory 279
12.25.2 Test Method 279
12.25.3 Interpretation 279
12.26 Stator Blackout Test 279
12.26.1 Purpose and Theory 280
12.26.2 Test Method 280
12.26.3 Interpretation 280
12.27 Stator Pressure and Vacuum Decay Test 281
12.27.1 Purpose and Theory 281
12.27.2 Test Methods and Interpretation 281
References 282
13 In-Service Monitoring of Stator and Rotor Windings 285
13.1 Thermal Monitoring 286
13.1.1 Stator Winding Point Sensors 286
13.1.2 Rotor Winding Sensors 288
13.1.3 Data Acquisition and Interpretation 288
13.1.4 Thermography 289
13.2 Condition Monitors and Tagging Compounds 290
13.2.1 Monitoring Principles 291
13.2.2 Interpretation 292
13.3 Ozone 293
13.3.1 Monitoring Principles 293
13.3.2 Interpretation 294
13.4 On-Line Partial Discharge Monitor 295
13.4.1 Monitoring Principles 295
13.4.2 Interpretation 302
13.5 End-Winding Vibration Monitor 307
13.5.1 Monitoring Principles 307
13.5.2 Data Acquisition and Interpretation 308
13.6 Synchronous Rotor Flux Monitor 308
13.6.1 Monitoring Principles 308
13.6.2 Data Acquisition and Interpretation 310
13.7 Current Signature Analysis 311
13.7.1 Monitoring Principles 311
13.7.2 Data Acquisition 313
13.7.3 Interpretation 314
13.8 Air Gap Monitoring for Salient Pole Machines 315
13.8.1 Monitoring Principles 315
13.9 Voltage Surge Monitor 316
13.9.1 Monitoring Principles 316
13.9.2 Interpretation 316
13.10 Bearing Vibration Monitor 317
13.10.1 Induction Motor Monitoring 317
13.10.2 Synchronous Machine Monitoring 318
References 319
14 Core Testing 321
14.1 Knife Test 321
14.1.1 Purpose and Theory 321
14.1.2 Test Method 322
14.1.3 Interpretation 322
14.2 Rated Flux Test 323
14.2.1 Purpose and Theory 323
14.2.2 Test Method 324
14.2.3 Interpretation 328
14.3 Core Loss Test 328
14.3.1 Purpose and Theory 328
14.3.2 Test Method 328
14.3.3 Interpretation 328
14.4 Low Core Flux Test (EL-CID) 329
14.4.1 Purpose and Theory 329
14.4.2 Test Method 330
14.4.3 Interpretation 331
References 332
15 Acceptance and Site Testing of New Windings 333
15.1 Stator Windings Insulation System Prequalification Tests 333
15.1.1 Power Factor Tip-Up Test 333
15.1.2 Partial Discharge Test 334
15.1.3 Impulse (Surge) Test 335
15.1.4 Voltage Endurance Test 335
15.1.5 Thermal Cycling Test 337
15.1.6 Thermal Classification Tests 338
15.2 Stator Winding Insulation System Factory and On-Site Tests 339
15.2.1 Insulation Resistance and Polarization Index Tests 339
15.2.2 AC and DC Hipot Tests 340
15.2.3 Impulse (Surge) Tests 341
15.2.4 Strand-to-Strand Test 342
15.2.5 Power Factor Tip-Up Test 342
15.2.6 Partial Discharge Test 343
15.2.7 Capacitance Test 343
15.2.8 Semiconductive Coating Test 344
15.2.9 Wedge Tap 344
15.3 Factory and On-Site Tests for Rotor Windings 345
15.3.1 Tests Applicable to All Insulated Windings 345
15.3.2 Round-Rotor Synchronous Machine Windings 346
15.3.3 Salient Pole Synchronous Machine Windings 347
15.3.4 Wound Induction Rotor Windings 347
15.3.5 Squirrel Cage Rotor Windings 347
15.4 Core Insulation Factory and On-Site Tests 348
15.4.1 Core Tightness Test 348
15.4.2 Rated Flux Test 348
15.4.3 EL-CID Test 349
References 350
16 Maintenance Strategies 351
16.1 Maintenance and Inspection Options 351
16.1.1 Breakdown or Corrective Maintenance 352
16.1.2 Time-Based or Preventative Maintenance 352
16.1.3 Condition-Based or Predictive Maintenance 354
16.1.4 Inspections 355
16.2 Maintenance Strategies for Various Machine Types and 357
16.2.1 Turbogenerators 357
16.2.2 Salient Pole Generators and Motors 359
16.2.3 Squirrel Cage and Wound-Rotor Induction Motors 361
Index 365
About the Authors 371
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