Provides coverage of Motor Current Signature Analysis (MCSA) for cage induction motors
This book is primarily for industrial engineers. It has 13 chapters and contains a unique data base of 50 industrial case histories on the application of MCSA to diagnose broken rotor bars or unacceptable levels of airgap eccentricity in cage induction motors with ratings from 127 kW (170 H.P.) up to 10,160 kW (13,620 H.P.). There are also unsuccessful case histories, which is another unique feature of the book. The case studies also illustrate the effects of mechanical load dynamics downstream of the motor on the interpretation of current signatures. A number of cases are presented where abnormal operation of the driven load was diagnosed. Chapter 13 presents a critical appraisal of MCSA including successes, failures and lessons learned via industrial case histories.
* The case histories are presented in a step by step format, with predictions and outcomes supported by current spectra and photographic evidence to confirm a correct or incorrect diagnosis
* The case histories are presented in detail so readers fully understand the diagnosis
* The authors have 108 years of combined experience in the installation, maintenance, repair, design, manufacture, operation and condition monitoring of SCIMs
* There are 10 questions at the end of chapters 1 to 12 and answers can be obtained via the publisher
Current Signature Analysis for Condition Monitoring of Cage Induction Motors serves as a reference for professional engineers, head electricians and technicians working with induction motors. To obtain the solutions manual for this book, please send an email to pressbooks@ieee.org.
William T. Thomson is Director and Consultant with EM Diagnostics Ltd, in Scotland. Prof. Thomson received a BSc (Hons) in Electrical Engineering in 1973 and an MSc in 1977 from the University of Strathclyde. He has published 72 papers on condition monitoring of induction motors in a variety of engineering journals such as IEEE Transactions (USA), IEE Proceedings (UK), and also at numerous International IEEE and IEE conferences. He is a senior member of the IEEE, a fellow of the IEE (IET) in the UK and a Chartered Professional Engineer registered in the UK.
Ian Culbert was a Rotating Machines Specialist at Iris Power Qualitrol since April 2002 until his very untimely death on 8th September, 2015. At this company he provided consulting services to customers, assisted in product development, trained sales and field service staff and reviewed stator winding partial discharge reports. He has co-authored two books on electrical machine insulation design, evaluation, aging, testing and repair and was principal author of a number of Electric Power Research Institute reports on motor repair. Ian was a Registered Professional Engineer in the Province of Ontario, Canada and a Senior Member of IEEE.

WILLIAM T. THOMSON is Director and Consultant with EM Diagnostics Ltd, in Scotland. Prof. Thomson received a BSc (Hons) in Electrical Engineering in 1973 and an MSc in 1977 from the University of Strathclyde. He has published 72 papers on condition monitoring of induction motors in a variety of engineering journals such as IEEE Transactions (USA), IEE Proceedings (UK), and also at numerous International IEEE and IEE conferences. He is a senior member of the IEEE, a fellow of the IEE (IET) in the UK and a Chartered Professional Engineer registered in the UK.

IAN CULBERT was a Rotating Machines Specialist at Iris Power Qualitrol since April 2002 until his very untimely death on 8th September, 2015. At this company he provided consulting services to customers, assisted in product development, trained sales and field service staff and reviewed stator winding partial discharge reports. He has co-authored two books on electrical machine insulation design, evaluation, aging, testing and repair and was principal author of a number of Electric Power Research Institute reports on motor repair. Ian was a Registered Professional Engineer in the Province of Ontario, Canada and a Senior Member of IEEE.

ABOUT THE AUTHORS xiii

OBITUARY TO IAN CULBERT xv

ACKNOWLEDGMENTS xvii

FOREWORD xix

PREFACE xxiii

NOMENCLATURE xxvii

ACRONYMS AND ABBREVIATIONS xxxiii

RELEVANT UNITS OF EQUIVALENCE USEFUL FOR THIS BOOK xxxv

CHAPTER 1 MOTOR CURRENT SIGNATURE ANALYSIS FOR INDUCTION MOTORS 1

1.0 Introduction 1

1.1 Historical Development of MCSA and Goals of This Book 4

1.2 Basic Theory of Operation of the 3-Phase Induction Motor 6

1.3 Starting and Run-Up Characteristics of SCIMs 20

1.4 Illustrations of Construction of a Large HV SCIM 29

1.5 Questions 33

References 34

CHAPTER 2 DESIGN, CONSTRUCTION, AND MANUFACTURE OF SQUIRREL CAGE ROTORS 39

2.0 Introduction 39

2.1 Aluminum and Copper Die-Cast Windings 40

2.2 Fabricated Squirrel Cage Windings 43

2.3 Design and Manufacturing Features of Squirrel Cage Rotor Windings to Minimize Failures 52

2.4 Questions 53

References 54

CHAPTER 3 CAUSES OF BREAKS IN SQUIRREL CAGE WINDINGS DURING DIRECT-ON-LINE STARTS AND STEADY-STATE OPERATION 55

3.0 Introduction 55

3.1 Mechanical Stresses and Consequential Forces on Rotor Bars and End Rings 56

3.2 Thermal Stresses in the Rotor Bars and End Rings 57

3.3 Broken Bars and End Rings Due to Combined Mechanical and Thermal Stresses When Starting High Inertia Loads 59

3.4 Rotor Bar Stresses Resulting from a Loose Slot Fit 60

3.5 Strengths and Weaknesses of Certain Bar and End Ring Shapes and Types of Joints 62

3.6 Pulsating Loads Due to Crushers and Compressors 62

3.7 Direct-On-Line Starting of Large Induction Motors Driving High Inertia Fans 63

3.8 Direct-On-Line Starting of Large Induction Motors Driving Centrifugal Pumps 66

3.9 Limitations on Repetitive Motor Starts 68

3.10 Criteria for Design of Squirrel Cage Rotor Windings 69

3.11 Samples of Breaks in Squirrel Cage Rotor Windings 72

3.12 Questions 77

References 77

Further Reading 78

CHAPTER 4 MOTOR CURRENT SIGNATURE ANALYSIS (MCSA) TO DETECT CAGE WINDING DEFECTS 79

4.0 Summary 79

4.1 Introduction 79

4.2 Derivation of Current Component at f (1 ¿ 2s) 82

4.3 Reasons for Current Component at f (1 + 2s) 83

4.4 Spectrum Analysis of Current 85

4.5 Severity Indicators for Assessing Condition of Cage Windings at Full-Load 93

4.6 The dB Broken Bar Severity Chart 110

4.7 Influence of Number of Rotor Bars and Pole Number on the Equivalent Broken Bar Factor with Measured dB Difference Values 111

4.8 Questions 116

References 118

CHAPTER 5 MCSA INDUSTRIAL CASE HISTORIES-DIAGNOSIS OF CAGE WINDING DEFECTS IN SCIMs DRIVING STEADY LOADS 119

5.0 Introduction and Summary of Case Histories 119

5.1 Case History (2000-2014)-Summary and Key Features 120

5.2 Case History (1983)-Summary and Key Features 122

5.3 Case History (1982)-Summary and Key Features 125

5.4 Case History (2002)-Summary and Key Features 128

5.5 Case History (1985-1987)-Summary and Key Features 133

5.6 Case History (2006)-Summary and Key Features 136

5.7 MCSA Case History (2004)-Summary and Key Features 139

5.8 MCSA Case History (2004)-Summary and Key Features 141

5.9 Questions 143

References 144

CHAPTER 6 MCSA CASE HISTORIES-DIAGNOSIS OF CAGE WINDING DEFECTS IN SCIMs FITTED WITH END RING RETAINING RINGS 147

6.0 Introduction and Summary of Case Histories 147

6.1 Case History (2006)-Summary 148

6.2 Concluding Remarks on this Challenging Case History 160

6.3 Case History (1990)-Summary and Key Features 161

6.4 Summary and Lessons Learned from Industrial Case Histories in Chapters 5 and 6 166

6.5 Questions 170

References 172

CHAPTER 7 MCSA CASE HISTORIES-CYCLIC LOADS CAN CAUSE FALSE POSITIVES OF CAGE WINDING BREAKS 173

7.1 Introduction and Summary of Case Histories 173

7.2 Case History (2006)-Effect of Gas Recycling in a Centrifugal Gas Compressor and the Detection of Broken Rotor Bars 179

7.3 Case History: False Positive of Broken Rotor Bars Due to Recycling of Gas in a Centrifugal Compressor 180

7.4 Two Case Histories (2002 and 2013)-Broken Rotor Bars in the Same SCIM without and with Gas Recycling in a Gas Compressor 185

7.5 Case History 1986-Fluid Coupling Dynamics Caused a False Positive of a Cage Winding Break 193

7.6 Questions 198

References 200

CHAPTER 8 MCSA CASE HISTORIES-SCIM DRIVES WITH SLOW SPEED GEARBOXES AND FLUCTUATING LOADS CAN GIVE FALSE POSITIVES OF BROKEN ROTOR BARS 201

8.1 Introduction and Summary of Case Histories 201

8.2 Case History (1989)-Slow Speed Coal Conveyor, Load Fluctuations, and Gearbox in the Drive Train 213

8.3 MCSA Case History (1990)-Possible False Positive of Broken Rotor Bars in a SCIM Driving a Coal Conveyor Via a Slow Speed Gearbox 216

8.4 Case History (1992)-Impossible to Analyze MCSA Data Due to Severe Random Current Fluctuations from The Mechanical Load Dynamics from the Coal Crusher 217

8.5 Case History (1995)-Successful Assessment of Cage Windings When the Load Current Fluctuations are Normal from a SCIM Driving Coal Crusher 221

8.6 Two Case Histories (2015)-False Positive of Broken Bars in One of the SCIMs Driving Thrusters on an FPSO If Influence of Drive Dynamics is Discounted 227

8.7 Questions 237

References 238

CHAPTER 9 MISCELLANEOUS MCSA CASE HISTORIES 241

9.0 Introduction and Summary of Case Histories 241

9.1 Possible False Positives of Cage Winding Breaks in Two 1850 kW SCIMs, Due to Number of Poles (2p) Equal to Number of Spider Support Arms (Sp) on Shaft (1991) 242

9.2 Case History (2007)-SCIM with Number of Poles Equal to Number of Kidney Shaped Axial Ducts in the Rotor-False Positive of Broken Bars Prevented by Load Changes 251

9.3 Two Case Histories (2005-2008)-Normal and Abnormal Pumping Dynamics in Two SCIM Seawater Lift Pump Drive Trains 253

9.4 MCSA Case History (2006-2007)-Slack and Worn Belt Drives in Two SCIM Cooling Fan Drives in a Cement Factory 259

9.5 Application of MCSA to Inverter-FED LV and HV SCIMs 263

9.6 Case History (1990)-Assessment of the Mechanical Operational Condition of an Electrical Submersible Pump (ESP) Driven by a SCIM Used in Artificial Oil Lift 267

9.7 Questions 270

References 271

CHAPTER 10 MCSA TO ESTIMATE THE OPERATIONAL AIRGAP ECCENTRICITY IN SQUIRREL CAGE INDUCTION MOTORS 273

10.0 Summary and Introduction 273

10.1 Definition of Airgap Eccentricity 274

10.2 Causes and Associated Types of Airgap Eccentricity 276

10.3 Unbalanced Magnetic Pull (UMP) and Rotor Pull-Over 281

10.4 Current Signature Pattern due to Airgap Eccentricity 284

10.5 Questions 294

References 295

CHAPTER 11 CASE HISTORIES-SUCCESSFUL AND UNSUCCESSFUL APPLICATION OF MCSA TO ESTIMATE OPERATIONAL AIRGAP ECCENTRICITY IN SCIMS 299

11.0 Summary and List of Case Histories 299

11.1 Flow Chart of MCSA Procedure to Estimate Operational Airgap Eccentricity 300

11.2 Case History (1989)-Low Level of Airgap Eccentricity in a SCIM Driving a Centrifugal Air Compressor 302

11.3 Two Case Histories (2004)-Operational Airgap Eccentricity in Nominally Identical SCIMs Driving Pumps in a CCGT Power Station 307

11.4 Four Case Histories (2005)-Abnormal Level of Airgap Eccentricity in a Large, Low Speed, HV Motor Driving a Cooling Water Pump in a Power Station 310

11.5 Case History (1988)-High Level of Airgap Eccentricity in an HV SCIM Driving a Pump in a Large Oil Storage Tank Facility 318

11.6 Case History (2001)-High Airgap Eccentricity in a Cooling Water Pump Motor that Caused Severe Mechanical Damage to HV Stator Coils 324

11.7 Case History (2008)-Unsuccessful Application of MCSA Applied to a Large (6300 kW), Inverter-FED, 6600 V SCIM During a No-Load Run to Assess Its Operational Airgap Eccentricity 332

11.8 Case History (2008)-Successful Application of MCSA Applied to a Large (4500 kW), Inverter-Fed, 3300 V SCIM to Assess its Operational Airgap Eccentricity 335

11.9 Case History (2007)-Advanced MCSA Interpretation of Current Spectra Was Required to Verify High Airgap Eccentricity in an HV SCIM Driving a Primary Air (PA) Fan in a Power Station 339

11.10 Case History (1990)-Unsuccessful MCSA Case History to Assess Operational Airgap Eccentricity in an HV SCIM Driving a Slow Speed Reciprocating Compressor 343

11.11 Case History (2002)-Predict Number of Rotor Slots and Assessment of Operational Airgap Eccentricity in a Large 6600 V, 6714 kW/9000 HP SCIM Driving a Centrifugal Compressor 347

11.12 Questions 353

References 357

CHAPTER 12 CRITICAL APPRAISAL OF MCSA TO DIAGNOSE SHORT CIRCUITED TURNS IN LV AND HV STATOR WINDINGS AND FAULTS IN ROLLER ELEMENT BEARINGS IN SCIMS 359

12.1 Summary 359

12.2 Shorted Turns in HV Stator Winding Coils 361

12.3 Detection of Shorted Turns Via MCSA under Controlled Experimental Conditions 364

12.4 Detection of Defects in Roller Element Bearings Via MCSA 368

12.5 Questions 371

References 372

CHAPTER 13 APPRAISAL OF MCSA INCLUDING LESSONS LEARNED VIA INDUSTRIAL CASE HISTORIES 375

13.1 Summary of MCSA in Industry to Diagnose Cage Winding Breaks 375

13.2 Flow Chart for Measurement and Analysis of Current to Diagnose Cage Winding Breaks 375

13.3 MCSA to Diagnose Broken Rotor Bars in SCIMs Driving Steady Loads 379

13.4 Number of Rotor Bars, External Constraints, and Lessons Learned 380

13.5 Effect of End Ring Retaining Rings (ERRS) on Diagnosis of Broken Rotor Bars 381

13.6 MCSA Applied to SCIMs Driving Complex Mechanical Plant, Lessons Learned, and Recommendations 382

13.7 Double Cage Rotors-Classical MCSA can only Detect Cage Winding Breaks in Inner Run Winding 382

13.8 MCSA to Diagnose Operational Levels of Airgap Eccentricity in SCIMs 383

13.9 Recommendations to End Users 385

13.10 Suggested Research and Development Projects 386

References 388

Appendix 13.A Commentary on Interpretation of LV and HV Used in SCIMs 388

LIST OF EQUATIONS 389

INDEX 393