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Library of Congress Cataloging-in-Publication Data is available.

ISBN: 978-1-119-02959-5

CONTENTS

About the Authors

Obituary to Ian Culbert (1943–2015)

Acknowledgments

Foreword

Preface

Nomenclature

Acronyms and Abbreviations

Relevant Units of Equivalence Useful for this Book

Chapter 1 Motor Current Signature Analysis for Induction Motors

1.0 Introduction
1.1 Historical Development of Mcsa and Goals of This Book
1.2 Basic Theory of Operation of the 3-phase Induction Motor
1.3 Starting and Run-up Characteristics of SCIMs
1.4 Illustrations of Construction of a Large hv Scim
1.5 Questions
References

Chapter 2 Design, Construction, and Manufacture of Squirrel Cage Rotors

2.0 Introduction
2.1 Aluminum and Copper Die-Cast Windings
2.2 Fabricated Squirrel Cage Windings
2.3 Design and Manufacturing Features of Squirrel Cage Rotor Windings to Minimize Failures
2.4 Questions
References

Chapter 3 Causes of Breaks in Squirrel Cage Windings During Direct-On-Line Starts and Steady-State Operation

3.0 Introduction
3.1 Mechanical Stresses and Consequential Forces on Rotor Bars and End Rings
3.2 Thermal Stresses in the Rotor Bars and End Rings
3.3 Broken Bars and End Rings Due to Combined Mechanical and Thermal Stresses When Starting High Inertia Loads
3.4 Rotor Bar Stresses Resulting From a Loose Slot Fit
3.5 Strengths and Weaknesses of Certain Bar and End Ring Shapes and Types of Joints
3.6 Pulsating Loads Due to Crushers and Compressors
3.7 Direct-On-Line Starting of Large Induction Motors Driving High Inertia Fans
3.8 Direct-On-Line Starting of Large Induction Motors Driving Centrifugal Pumps
3.9 Limitations on Repetitive Motor Starts
3.10 Criteria for Design of Squirrel Cage Rotor Windings
3.11 Samples of Breaks in Squirrel Cage Rotor Windings
3.12 Questions
References
Further Reading

Chapter 4 Motor Current Signature Analysis (MCSA) to Detect Cage Winding Defects

4.0 Summary
4.1 Introduction
4.2 Derivation of Current Component at f (1 − 2s)
4.3 Reasons for Current Component at f (1 + 2s)
4.4 Spectrum Analysis of Current
4.5 Severity Indicators for Assessing Condition of Cage Windings at Full-Load
4.6 The dB Broken Bar Severity Chart
4.7 Influence of Number of Rotor Bars and Pole Number on the Equivalent Broken Bar Factor with Measured dB Difference Values
4.8 Questions
References

Chapter 5 MCSA Industrial Case Histories—Diagnosis of Cage Winding Defects in SCIMs Driving Steady Loads

5.0 Introduction and Summary of Case Histories
5.1 Case History (2000–2014)—Summary and Key Features
5.2 Case History (1983)—Summary and Key Features
5.3 Case History (1982)—Summary and Key Features
5.4 Case History (2002)—Summary and Key Features
5.5 Case History (1985–1987)—Summary and Key Features
5.6 Case History (2006)—Summary and Key Features
5.7 MCSA Case History (2004)—Summary and Key Features
5.8 MCSA Case History (2004)—Summary and Key Features
5.9 Questions
References

Chapter 6 MCSA Case Histories—Diagnosis of Cage Winding Defects in SCIMs Fitted with End Ring Retaining Rings

6.0 Introduction and Summary of Case Histories
6.1 Case History (2006)—Summary
6.2 Concluding Remarks on this Challenging Case History
6.3 Case History (1990)—Summary and Key Features
6.4 Summary and Lessons Learned from Industrial Case Histories in Chapters 5 and 6
6.5 Questions
References

Chapter 7 MCSA Case Histories—Cyclic Loads Can Cause False Positives of Cage Winding Breaks

7.1 Introduction and Summary of Case Histories
7.2 Case History (2006)—Effect of Gas Recycling in a Centrifugal Gas Compressor and the Detection of Broken Rotor Bars
7.3 Case History: False Positive of Broken Rotor Bars Due to Recycling of Gas in a Centrifugal Compressor
7.4 Two Case Histories (2002 and 2013)—Broken Rotor Bars in the Same Scim Without and With Gas Recycling in a Gas Compressor
7.5 Case History 1986–Fluid Coupling Dynamics Caused a False Positive of a Cage Winding Break
Appendix 7.a.1 Derivation of Sidebands due to Low Frequency Oscillation from the Mechanical Load
7.6 Questions
References

Chapter 8 MCSA Case Histories—SCIM Drives With Slow Speed Gearboxes and Fluctuating Loads Can Give False Positives Of Broken Rotor Bars

8.1 Introduction and Summary of Case Histories
8.2 Case History (1989)—Slow Speed Coal Conveyor, Load Fluctuations, and Gearbox in the Drive Train
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
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
8.5 Case History (1995)—Successful Assessment of Cage Windings When the Load Current Fluctuations are Normal from a SCIM Driving Coal Crusher
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
8.7 Questions
References

Chapter 9 Miscellaneous MCSA Case Histories

9.0 Introduction and Summary of Case Histories
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 (S_p) on Shaft (1991)
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
9.3 Two Case Histories (2005–2008)—Normal and Abnormal Pumping Dynamics in Two SCIM Seawater Lift Pump Drive Trains
9.4 MCSA Case History (2006–2007)—Slack and Worn Belt Drives in Two SCIM Cooling Fan Drives in a Cement Factory
9.5 Application of MCSA to Inverter-FED LV and HV SCIMs
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
9.7 Questions
References

Chapter 10 MCSA to Estimate the Operational Airgap Eccentricity in Squirrel Cage Induction Motors

10.0 Summary and Introduction
10.1 Definition of Airgap Eccentricity
10.2 Causes and Associated Types of Airgap Eccentricity
10.3 Unbalanced Magnetic Pull (UMP) and Rotor Pull-Over
10.4 Current Signature Pattern due to Airgap Eccentricity
10.5 Questions
References

Chapter 11 Case Histories—Successful and Unsuccessful Application of MCSA to Estimate Operational Airgap Eccentricity in SCIMs

11.0 Summary and List of Case Histories
11.1 Flow Chart of MCSA Procedure to Estimate Operational Airgap Eccentricity
11.2 Case History (1989)—Low Level of Airgap Eccentricity in a Scim Driving a Centrifugal Air Compressor
11.3 Two Case Histories (2004)—Operational Airgap Eccentricity in Nominally Identical SCIMs Driving Pumps in a CCGT Power Station
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
11.5 Case History (1988)—High Level of Airgap Eccentricity in an HV Scim Driving a Pump in a Large Oil Storage Tank Facility
11.6 Case History (2001)—High Airgap Eccentricity in a Cooling Water Pump Motor that Caused Severe Mechanical Damage to HV Stator Coils
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
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
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
11.10 Case History (1990)—Unsuccessful MCSA Case History to Assess Operational Airgap Eccentricity in an HV Scim Driving a Slow Speed Reciprocating Compressor
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
11.12 Questions
References

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

12.1 Summary
12.2 Shorted Turns in HV Stator Winding Coils
12.3 Detection of Shorted Turns VIA MCSA Under Controlled Experimental Conditions
12.4 Detection of Defects in Roller Element Bearings VIA MCSA
12.5 Questions
Notes
References

Chapter 13 Appraisal of MCSA Including Lessons Learned via Industrial Case Histories

13.1 Summary of MCSA in Industry to Diagnose Cage Winding Breaks
13.2 Flow Chart for Measurement and Analysis of Current to Diagnose Cage Winding Breaks
13.3 MCSA to Diagnose Broken Rotor Bars in Scims Driving Steady Loads
13.4 Number of Rotor Bars, External Constraints, and Lessons Learned
13.5 Effect of End Ring Retaining Rings (ERRS) on Diagnosis of Broken Rotor Bars
13.6 MCSA Applied to SCIMs Driving Complex Mechanical Plant, Lessons Learned, and Recommendations
13.7 Double Cage Rotors—Classical MCSA can only Detect Cage Winding Breaks in Inner Run Winding
13.8 MCSA to Diagnose Operational Levels of Airgap Eccentricity in SCIMs
13.9 Recommendations to End Users
13.10 Suggested Research and Development Projects
References
Appendix 13.A Commentary on Interpretation of LV and HV used in SCIMs

List of Equations

Index

IEEE Press Series on Power Engineering

EULA

List of Tables

Chapter 1

Table 1.1
Table 1.2
Table 1.3

Chapter 3

Table 3.1
Table 3.2

Chapter 4

Table 4.1
Table 4.2
Table 4.3
Table 4.4
Table 4.2A
Table 4.2
Table 4.3
Table 4.8

Chapter 5

Table 5.1
Table 5.2
Table 5.3
Table 5.4
Table 5.5
Table 5.6
Table 5.7
Table 5.8

Chapter 6

Table 6.1
Table 6.2
Table 6.3

Chapter 7

Table 7.1

Chapter 9

Table 9.1

Chapter 10

Table 10.1
Table 10.2
Table 10.3
EXTRACT FROM TABLE 10.3
AN EXTRACT FROM TABLE 10.3
AN EXTRACT FROM TABLE 10.3
AN EXTRACT FROM TABLE 10.3
AN EXTRACT FROM TABLE 10.3
AN EXTRACT FROM TABLE 10.3

Chapter 11

Table 11.1
Table 11.2
Table 11.3

List of Illustrations

Chapter 1

Figure 1.1 Example of an unwound stator core. Reproduced with permission of Nidec Corporation, US Electric Motors Division.
Figure 1.2 HV winding inserted into the stator core. Reproduced with permission of Nidec Corporation, US Electric Motors Division.
Figure 1.3 Complete HV stator core assembly. Reproduced with permission of Baldor Electric Company, USA, a member of the ABB group.
Figure 1.3a Sectional view of 3-phase SCIM. Reproduced with permission of Baldor Electric Company, USA, a member of the ABB group.
Figure 1.4 3-phase HV stator winding assembly.
Figure 1.5 Schematic illustration of a squirrel cage copper or aluminum fabricated winding.
Figure 1.6 Copper fabricated squirrel cage rotor.
Figure 1.7 Squirrel cage rotor with a broken rotor bar that has lifted. Source: Thomson and Fenger [13]. Reproduced with permission of IEEE.
Figure 1.8a Induction motor action.
Figure 1.8b Finite element plot of distribution of magnetic field in an 8-pole induction motor. Reproduced with permission of EM Diagnostics Ltd.
Figure 1.9 Finite element model showing the magnetic flux lines taking the path of least magnetic reluctance through the stator and rotor teeth to cross the airgap. Reproduced with permission of EM Diagnostics Ltd.
Figure 1.10 Illustration of slip speed in r/min.
Figure 1.11 Illustration of forward rotating field N_fr from rotor currents.
Figure 1.12 Nameplate from a 6.6 kV, 760 kW/1018 HP, 60 Hz SCIM.
Figure 1.13 Photo of a nameplate from a 4160 V, 500 HP/373 kW, SCIM, reproduced by kind permission of © Baldor Electric Company, USA, a member of the ABB group.
Figure 1.14 Current versus speed. Reproduced with permission of Parsons Peebles, Scotland.
Figure 1.15 Torque versus speed curve for the motor. Reproduced with permission of Parsons Peebles, Scotland.
Figure 1.15a Speed versus torque for the operating region between no-load and full-load.
Figure 1.16 Torque versus speed curves for the motor and load. Reproduced with permission of Parsons Peebles, Scotland.
Figure 1.17 Per unit torque versus percentage of synchronous speed—step-by-step illustration to calculate the run-up time.
Figure 1.18 Motor torque (100% volts), motor torque (80% volts), and load torque versus synchronous speed—step-by-step calculation of run-up times at different applied volts.
Figure 1.19 Run-up time versus speed for 100% and 80 % volts driving a reciprocating compressor.
Figure 1.20 3-phase, 13,800 V, 5720 kW/7668 HP, 60 Hz, 1774 r/min SCIM, ready for delivery to the client. Reproduced with permission of Parsons Peebles, Scotland.
Figure 1.21 Sectional view of frame assembly. Reproduced with permission of Parsons Peebles, Scotland.
Figure 1.22 Sectional view of frame and stator assembly. Reproduced with permission of Parsons Peebles, Scotland.
Figure 1.23 Sectional view of frame, stator, and rotor. Reproduced with permission of Parsons Peebles, Scotland.
Figure 1.24 Stator core laminations. Reproduced with permission of Parsons Peebles, Scotland.
Figure 1.25 Squirrel cage rotor. Reproduced with permission of Parsons Peebles, Scotland.
Figure 1.26 HV stator winding and core in process of varnishing. Reproduced with permission of Parsons Peebles, Scotland.

Chapter 2

Figure 2.1 Rotor core with molds on either end ready for die-casting.
Figure 2.2 Die-cast aluminum rotor cage winding without the rotor core.
Figure 2.3 (a) and (b) Examples of aluminum die-cast cage rotors.
Figure 2.4 Illustration of skin effect in rotor bar.
Figure 2.5 Examples of different bar shapes.
Figure 2.6 Swaging.
Figure 2.7 Bar with sharp corners installed in slot with round corners.
Figure 2.8 Slot liner.
Figure 2.9a Simplified illustration of a key under bar.
Figure 2.9b Actual designs before and after fitting steel locking keys. Reproduced with permission of Parsons Peebles, Scotland.
Figure 2.9c Key bars fitted under copper bars. Reproduced with permission of Parsons Peebles, Scotland.
Figure 2.10 Butt connection.
Figure 2.11 Butt connection with groove machined in end ring.
Figure 2.12 End ring under rotor bars.
Figure 2.13 Weld joint in fabricated aluminum winding. Source: Finley and Hodowanec [12]. Reproduced with permission of IEEE.
Figure 2.14 Rotor bars in slotted end ring.
Figure 2.15 Illustration of good concave meniscus at the edges of the interface between bars and end rings and a poor finish.
Figure 2.16 Retaining ring over end ring. Photo taken by Ian Culbert. Reproduced with permission of Iris Power Qualitrol.
Figure 2.17 Retaining ring over end ring and bar extensions outside rotor slots. Photo taken by Ian Culbert. Reproduced with permission of Iris Power Qualitrol.

Chapter 3

Figure 3.1 Mechanical stresses on squirrel cage winding [8].
Figure 3.2 Bar bowing outside rotor slots due to differential thermal expansion.
Figure 3.3 High stresses in aluminum squirrel cage winding with no bar extensions beyond core.
Figure 3.4 Distortion of rotor end winding due to combined mechanical and thermal stresses.
Figure 3.5a Illustration of radial force on the rotor bars, F∝I²_rb and vibration.
Figure 3.5b Core burning at the top of the rotor slots, possible cause due to loose bars. Reproduced with permission of EASA, USA.
Figure 3.6 Motor driving a reciprocating compressor showing fluctuations in all 3-phase currents. Source: Perrin et al. [12]. Reproduced with permission of IEEE.
Figure 3.7 Motor and centrifugal fan torque versus speed curves.
Figure 3.8 Centrifugal pump torque versus speed curves with discharge valve open and closed.
Figure 3.9 Increased squirrel cage winding temperature during direct-on-line starting of high inertia fans due to repeated starts.
Figure 3.10 Failed joint in a copper cage in a SCIM driving an ID high inertia fan, caused by thermal and mechanical cyclic stresses. Reproduced with permission of EASA, USA.
Figure 3.11 The fractured bars were staked to prevent axial movement. Thermal expansion of the cage exerted a tensile stress, which eventually led to the staked bars fracturing. Reproduced with permission of EASA, USA.
Figure 3.12 Cracked end ring in die-cast aluminum cage winding. Reproduced with permission of EASA, USA.
Figure 3.13 Voids in die-cast aluminum cage winding. Reproduced with permission of EASA, USA.
Figure 3.14 Catastrophic failure of die-cast aluminum cage winding, overheated while running caused by overload, too many sequential starts, high ambient temperature. Reproduced with permission of EASA, USA.
Figure 3.15 Fabricated aluminum cage winding bar breaks in slot region, due to absence of airflow through the ducts during sequential starts. Reproduced with permission of EASA, USA.
Figure 3.16 Crack in a cage end ring of a SCIM driving an ID fan motor, causes are due to cyclic thermal and mechanical stresses. Photo taken by Ian Culbert. Reproduced with permission of Iris Power Qualitrol.
Figure 3.17 A 2-pole boiler feed pump motor cage winding with two broken bars at edge of retaining ring. The core laminations are burnt due to the flow of inter-bar currents through the core from the broken bars to adjacent healthy ones. Reproduced with permission of EASA, USA.
Figure 3.18 Fabricated copper cage winding with breaks in bars and end ring. Reproduced with permission of EASA, USA.
Figure 3.19 Fabricated copper cage winding with two broken bars, which have lifted out of the slots, caused by too many sequential DOL starts, bars were not originally tight enough in the slots. Source: Thomson and Fenger [20]. Reproduced with permission of IEEE.
Figure 3.20 Fabricated copper cage winding, which was not fit for purpose due to the deep thin bars experiencing very high temperatures during frequent DOL starts. The motor was driving a crane on an offshore platfrom and during very cold conditions the lubrication system became “very stiff” and caused long run-up times due to the increased torque demands during run-up.
Figure 3.21 Fabricated copper cage winding with one completely broken bar that has lifted out of its slot. The causes were too many DOL starts enhanced by this bar not being tight enough in the slot.

Chapter 4

Figure 4.1 Variation of amplitude of f(1 − 2s) component of stator current against rotor speed. Source: Williamson and Smith [4]. Reproduced with permission of IET.
Figure 4.2 Forward and backward rotating fields when a broken bar exists.
Figure 4.3 Illustration of ± 2sf sidebands around supply component.
Figure 4.4 An “idealized illustration” of a time domain current waveform, due to amplitude modulation caused by ± 2sf sidebands around the supply frequency produced by broken rotor bars.
Figure 4.5 Illustration of dB difference N between sidebands and supply component.
Figure 4.6 Illustration of measurement of current and MCSA instrumentation. Source: Thomson et al. [11]. Reproduced with permission of IEEE.
Figure 4.7 Typical layout of HV circuit breakers and instrumentation cubicles for HV motors.
Figure 4.8 MCSA clip-on CT around the secondary side of the in situ CT, which feeds the panel ammeter displaying the motor's current.
Figure 4.9 MCSA clip-on CT around one of the 3-phases external to the motor's circuit breaker in a power station.
Figure 4.10 Current zoom spectrum oil export pump motor, 12,800 line spectrum, 0–130 Hz, frequency resolution .
Figure 4.11 Current zoom spectrum oil booster pump motor, 12,800 line spectrum, 0–130 Hz, frequency resolution .
Figure 4.12a Test rig for testing a SCIM with rotors having broken rotor bars. Constructed by Donald Sutherland, formerly of the Robert Gordon University, Aberdeen, Scotland.
Figure 4.12b Test rig for testing a SCIM to clearly show all coil ends were available for connecting the stator with different pole numbers. Constructed by Donald Sutherland, formerly of the Robert Gordon University, Aberdeen, Scotland.
Figure 4.13 Test rig with a scaled down frame of a typical design used in a large high power SCIM. Used for airgap eccentricity experiments. Constructed by Donald Sutherland, formerly of the Robert Gordon University, Aberdeen, Scotland.
Figure 4.14 Test rig for airgap eccentricity experiments using a 51 slot rotor with a long flexible rotor assembly.
Figure 4.15 Current spectrum, no broken bars, full-load slip of 4.67%, at a full-load current of 20.5 A.
Figure 4.16 Current spectrum, one broken bar, and full-load current at 20.5 A and a full-load slip of 4.67%.
Figure 4.17 Current spectrum, two broken bars, full-load current 20.5 A, full-load slip of 4.67%.
Figure 4.18 The 51 slot aluminum die-cast rotor with 10 broken rotor bars.
Figure 4.19 Current spectrum, 10 broken bars, and a slip of 5.73%.
Figure 4.20 Current spectrum, one broken bar, and operating current 14.5A at a slip of 2.2%, that is, 45% of the full-load slip.
Figure 4.21 Plot of N, the dB difference between the lower 2sf sideband and the supply component versus input current, and output speed with one broken rotor bar.
Figure 4.22 BB_f versus number of rotor bars for 2-pole motors with various N_av dB differences.
Figure 4.23 BB_f versus number of rotor bars for 4-pole motors with various N_av dB differences.
Figure 4.24 BB_f versus number of rotor bars for 12-pole motors with various N_av dB differences.

Chapter 5

Figure 5.1 Current zoom spectrum, full-load amperes, 12,800 lines, baseband 0–130 Hz, 10.16 mHz/line.
Figure 5.2 Sidebands due to broken rotor bars, 10.16 mHz/line. Source: Thomson and Fenger [1]. Reproduced with permission of IEEE.
Figure 5.3 Severely damaged cage winding, overheated rotor core. Source: Thomson and Fenger [1]. Reproduced with permission of IEEE.
Figure 5.4 Current spectrum of motor A, 10.16 mHz/line.
Figure 5.5 Current spectrum of motor B, 10.16 mHz/line.
Figure 5.6 Cage rotor, no signs of overheating or external damage. Source: Thomson and Fenger [3]. Reproduced with permission of IEEE.
Figure 5.7 Shows the faulty cage winding after the dissection was completed.
Figure 5.8 Photo of rotor.
Figure 5.9 Current zoom spectrum, line resolution 10.16 mHz/line.
Figure 5.10 Close up of the cage rotor with one broken rotor bar.
Figure 5.11 Overview of damaged stator winding and core.
Figure 5.12 Close up of the damaged stator winding and core.
Figure 5.13 Current spectrum, 1985.
Figure 5.14 Current spectrum, multiple broken rotor bars, 1987.
Figure 5.15 Rotor showing broken bars.
Figure 5.16 Visual inspection after cleaning and prior to NDT dye penetrant test.
Figure 5.17 Motor A) current spectrum, 10.16 mHz/line.
Figure 5.18 Motor B current spectrum, 10.16 mHz/line.
Figure 5.19 (a) and (b) A sample of 1 out of 10 faulty joints is shown by the leakage of the dye penetrant—that is the dark parts shown.
Figure 5.20 Current spectrum indicating ± 2sf and ± 4sf sidebands, 10.16 mHz/line.
Figure 5.21 Current spectrum, note the zoom spectrum analysis gives a frequency resolution of 0.063 Hz/division to cope with a full-load slip of 0.44% and the line resolution is 0.10 Hz/line.

Chapter 6

Figure 6.1 Multiple broken rotor bars.
Figure 6.2 Stator winding (13.8 kV) failure.
Figure 6.3 Pear or sash bar shape rounded at the end.
Figure 6.4 Showing ERR, initial evidence of faulty joints.
Figure 6.5 Current zoom spectrum, baseband span 0–130 Hz, 12,800 lines, 10.16 mHz/line, 80 dB dynamic range.
Figure 6.6 Zoomed current zoom spectrum to detect f_rs, baseband span 70–3400 Hz, 12,8000 line, 0.26 Hz/line.
Figure 6.7 End ring retaining ring removed, faulty joints.
Figure 6.8 Broken rotor bar still making contact with end ring.
Figure 6.9 End ring removed.
Figure 6.10 Ten broken rotor bars at the DE.
Figure 6.11 Torque–speed curves for a centrifugal pump: open and closed valve settings.
Figure 6.12 Torque–speed curves for motor (M₁: 100%, M₂: 90%, and M₃: 80%) volts and centrifugal pump curves, P₁: closed valve setting, P₂: open valve setting.
Figure 6.13a Voltage and current waveforms immediately after switch on.
Figure 6.13b Torque versus speed curves for new motor at 100% and 80% rated volts and for the centrifugal pump with closed and open valve settings.
Figure 6.14 Rotor design in brand new motor. Reproduced with permission of Parsons Peebles, Scotland.
Figure 6.15 Rotor showing large end ring retaining rings (ERRs).
Figure 6.16 Normal current spectrum, motor A.
Figure 6.17 Current spectrum with very low level ±2sf sidebands, motor B.
Figure 6.18 Current spectrum with ±2sf sidebands from motor C, which are up to 23 dB (factor of 14 in absolute amperes) higher than in motor B.
Figure 6.19 All bars cut, evidence of a broken rotor bar.
Figure 6.20 Dye penetrant (dark areas) applied to the end ring.
Figure 6.21 Developer applied, dark areas show 46% of 52 joints were inferior.
Figure 6.22 Sample of faulty joints (dark portions at the joints) on inside face of the DE ring.
Figure 6.23View of DE of the motor. Reproduced with permission of Quartzelec, Aberdeen, Scotland.
Figure 6.24 Survey of module and space for the lift. Reproduced with permission of Quartzelec, Aberdeen, Scotland.
Figure 6.25 The cooler has been removed. Reproduced with permission of Quartzelec, Aberdeen, Scotland.
Figure 6.26 Photo of the crane set up. Reproduced with permission of Quartzelec, Aberdeen, Scotland.
Figure 6.27 The lift in progress. Reproduced with permission of Quartzelec, Aberdeen Scotland.
Figure 6.28 Motor on upper module deck. Reproduced with permission of Quartzelec, Aberdeen Scotland.
Figure 6.29 The rotor being removed. Reproduced with permission of Quartzelec, Aberdeen, Scotland.
Figure 6.30 The rotor onshore for inspection. Reproduced with permission of Quartzelec, Aberdeen, Scotland.

Chapter 7

Figure 7.1 Current spectrum, one broken bar (slip 4%), no external load oscillations, line resolution 10.16 mHz/line.
Figure 7.2 Current spectrum, one broken bar (mean slip 4%) and external load oscillations, line resolution 10.16 mHz/line.
Figure 7.3 Current spectrum, one broken bar (mean slip 1%) and external load oscillations, line resolution 10.16 mHz/line.
Figure 7.4 Current spectrum, recycling of gas in compressor, f_c = 0.15 Hz is the frequency of the cyclic disturbance from gas recycling, line resolution 10.16 mHz/line.
Figure 7.5 Case one, current spectrum, no recycling of gas, line resolution 10.16 mHz/line.
Figure 7.6 Current spectrum, “nominally” no recycling in the compressor, 2006, line resolution 10.16 mHz/line.
Figure 7.7 Current spectrum showing the rotor slot passing frequency, baseband span 70–2500 Hz, 12,800 lines, 0.19 Hz/line.
Figure 7.8 Current spectrum, recycling in the compressor, 2007, line resolution 10.16 mHz/line.
Figure 7.9 Photograph of rotor.
Figure 7.10 No evidence of broken, cracked bars or faulty joints in the cage winding.
Figure 7.11 Case two, current spectrum, recycling of gas, 2008, brand new rotor, line resolution 10.16 mHz/line.
Figure 7.12 Current spectrum in 2002 with ±2sf and ±4sf sidebands, line resolution 10.16 mHz/line.
Figure 7.13 One broken rotor bar and an overheated adjacent rotor bar.
Figure 7.14 Current spectrum in 2012 with numerous sidebands, compressor on recycling, line resolution 10.16 mHz/line.
Figure 7.15a Current spectrum in 2013 showing sidebands at 0.67 Hz around f, compressor was on gas recycling, line resolution 10.16 mHz/line.
Figure 7.15b Measurement of f_{rs( + 1)}, baseband span 70–1800 Hz, 12,800 lines, line resolution 135 mHz/line.
Figure 7.16 Current spectrum (same load at 98 A) on June 3–4, 2013, showing sidebands at ±2sf with the compressor on recycling; baseband span of 0–55 Hz, 12,800 lines, frequency resolution of 4.3 mHz/line.
Figure 7.17 Rotor construction showing skewed rotor bars and broken rotor bars.
Figure 7.18 NDE: one completely broken bar, and two adjacent broken bars that were still in partial contact with the end ring, core damage.
Figure 7.19 DE: one completely broken bar.
Figure 7.20 Current spectrum in 1984, sidebands incorrectly identified to be at ±2sf and ±4sf since they were from fluid coupling dynamics.
Figure 7.21 Region of rough finished bar to end ring joints at the NDE.
Figure 7.22 Illustration of bar to end ring joint length.
Figure 7.23 Illustration of actual bar to end ring joint length in faulty region.
Figure 7.A1 Approximate equivalent circuit per phase referred to the stator input terminal for a 3-phase induction motor.

Chapter 8

Figure 8.1 Illustration of parallel misalignment.
Figure 8.2 Illustration of axial misalignment.
Figure 8.3 Illustration of angular misalignment.
Figure 8.4 Misaligned shafts prior to coupling being made up.
Figure 8.5 Deflected shape after coupling is made up.
Figure 8.6 Schematic illustration of only static airgap eccentricity.
Figure 8.7 Schematic illustration of only dynamic airgap eccentricity.
Figure 8.8 Close up of SCIM under test.
Figure 8.9 Current spectrum—no broken bars, minimum parallel misalignment of 0.05 mm (2 mils), 25 mHz/line.
Figure 8.10 Current spectrum—no broken bars, parallel misalignment of 0.2 mm (8 mils), 25 mHz/line.
Figure 8.11 Magnitude in dB of f ± f_r (Hz) components as a function of external misalignment, but with a fixed airgap eccentricity as set internally within the SCIM.
Figure 8.12 Illustration of gearbox information; T1 = 38 teeth, T2 = 56 teeth, T3 = 30 teeth, and T4 = 55 teeth.
Figure 8.13 Current spectrum, no gearbox, 25 mHz/line.
Figure 8.14 Current spectrum, with brand new gearbox, 25 mHz/line.
Figure 8.15 Schematic illustration of drive train.
Figure 8.16 Current zoom spectrum, baseband span 0–130 Hz, 12,800 lines, 10.16 mHz/line.
Figure 8.17 Current spectrum, baseband span 0–100 Hz, 6400 lines, 15.6 mHz/line.
Figure 8.18 Current zoom spectrum 45–55 Hz, 10% of spectrum in Figure 8.17, 15.6 mHz/line.
Figure 8.19 Typical coal crusher in a coal fired power station. Reproduced with permission of EM Diagnostics Ltd.
Figure 8.20 Current waveform, 20 cycles of 50 Hz supply.
Figure 8.21 Three-stage reduction gearbox, overall step down ratio of 36.146^*.
Figure 8.22 Motor A, current spectrum, span 0–100 Hz, line resolution 15.6 mHz/line.
Figure 8.23 Motor A, current zoom spectrum 45–55 Hz, 10% of spectrum in Figure 8.22, 15.6 mHz/line.
Figure 8.24 Illustration of coal crusher drive train.
Figure 8.25 Time domain current, two cycles from motor A.
Figure 8.26 Time domain current, 400 cycles from motor A, current swinging between 65 and 90 A on an in situ panel ammeter.
Figure 8.27 Time domain current, two cycles from motor B.
Figure 8.28 Time domain current, 200 cycles from motor B, current swinging between 50 and 100 A on an in situ panel ammeter.
Figure 8.29 Current spectrum, motor A, 6400 lines, baseband span 100 Hz, frequency resolution 15.63 mHz/line, current swing 65–90 A.
Figure 8.30 Current spectrum, motor B, 6400 lines, baseband span 100 Hz, frequency resolution 15.63 mHz/line, current swing 50–100 A.
Figure 8.31 Motor A, current zoom spectrum, rotor slot passing frequencies, baseband span 70–1800 Hz, 12,800 lines, 135 mHz/line.
Figure 8.32 Current zoom spectrum, motor A, 15.63 mHz/line.
Figure 8.33 Current zoom spectrum, motor B, 15.63 mHz/line.
Figure 8.34 Schematic illustration of the main HV SCIM drives on this FPSO.
Figure 8.35 Illustration of drive train and photo of the top side gearbox (TSBGB). Reproduced with permission of EM Diagnostics Ltd.
Figure 8.36 Current zoom spectrum for PTM, 10.16 mHz/line.
Figure 8.37 Current zoom spectrum for STM, 10.16 mHz/line.
Figure 8.38 Current spectrum from STM, 106 A, 50° pitch, baseband span (0–130 Hz), 12,800 lines, 10.16 mHz/line.
Figure 8.39 Current spectrum from PTM, 106 A, 50° pitch, baseband span (0–130 Hz), 12,800 lines, 10.16 mHz/line.
Figure 8.40 Current spectrum from STM, 106 A, 50° pitch, baseband span (0–130 Hz), 12,800 lines, 10.16 mHz/line.
Figure 8.41 Current spectrum from PTM, 106 A, 50° pitch, baseband span (0–130 Hz), 12,800 lines, 10.16 mHz/line.
Figure 8.42 Current zoom spectrum around f − 2f_r from PTM, 106 A, 50° pitch, baseband span (0–130 Hz), 12,800 lines, 10.16 mHz/line.
Figure 8.43 Current spectrum around f + 2f_r from PTM, 106 A, 50° pitch, baseband span (0–130 Hz), 12,800 lines, 10.16 mHz/line.
Figure 8.44 Hull of an FPSO in dry dock. Reproduced with permission of BW Offshore (UK) Ltd., Aberdeen, Scotland.
Figure 8.45 Close up, thruster propeller. Reproduced with permission of BW Offshore (UK) Ltd., Aberdeen, Scotland.
Figure 8.46 Rope wrapped around the propeller. Reproduced with permission of BW Offshore, (UK) Ltd., Aberdeen, Scotland.
Figure 8.47 Two largish chips on propeller blade. Reproduced with permission of BW Offshore (UK) Ltd., Aberdeen, Scotland.
Figure 8.48 Chip on propeller blade. Reproduced with permission of BW Offshore (UK) Ltd., Aberdeen, Scotland.
Figure 9.1a 4-pole magnetic field with four spiders at one instant in time.
Figure 9.1b 4-pole magnetic field moved forward by 90° electrical.
Figure 9.2a Equivalent magnetic circuit for one pole of Figure 9.1a.
Figure 9.2b Equivalent magnetic circuit for one pole of Figure 9.1b.
Figure 9.3 Rotor, no broken rotor bars.
Figure 9.4 Rotor shaft to show spider support arms (4 of) and axial cooling ducts (4 of).
Figure 9.5 Motor A, 120 A, current zoom spectrum, 10.16 mHz/line.
Figure 9.6 Motor B, 124 A, current zoom spectrum, 10.16 mHz/line.
Figure 9.7 Current spectrum, 272 A, operating slip of 0.54%, 10.16 mHz/line.
Figure 9.8 Current spectrum, 167 A, operating slip of 0.25%, 10.16 mHz/line.
Figure 9.9 Special rotor cage construction for submersible SCIM.
Figure 9.10 2005 motor A, 62 A, current zoom spectrum, 10.16 mHz/line.
Figure 9.11 2005 motor B, 64 A, current zoom spectrum, 10.16 mHz/line.
Figure 9.12 2005 motor A, 62 A, current spectrum, 10.16 mHz/line.
Figure 9.13 2005 motor B, 64 A, current spectrum, 10.16 mHz/line.
Figure 9.14 2008 motor A, 62–67 A, current zoom spectrum, 10.16 mHz/line.
Figure 9.15 2008 motor B, 67 A, current zoom spectrum, 10.16 mHz/line.
Figure 9.16 2008 motor A, 62–67 A, current spectrum, 10.16 mHz/line.
Figure 9.17 2008 motor B, 67 A, current zoom spectrum, 10.16 mHz/line.
Figure 9.18 Photograph of the damaged caisson. Reproduced with permission of EM Diagnostics Ltd.
Figure 9.19 Motor A, current zoom spectrum, 10.16 mHz/line.
Figure 9.20 Motor B, current zoom spectrum,10.16 mHz/line.
Figure 9.21 Motor drive A, current spectrum, November 2006, 10.16 mHz/line.
Figure 9.22 Motor drive B, current spectrum November 2006, 10.16 mHz/line.
Figure 9.23 Motor drive A, current spectrum, retest in March 2007 after new belts fitted, 10.16 mHz/line.
Figure 9.24 Motor drive B, current spectrum, retest in March 2007, same belts as in November 2006, 10.16 mHz/line.
Figure 9.25 Time domain current waveform.
Figure 9.26 Current zoom spectrum, 10.16 mHz/line.
Figure 9.27 Current zoom spectrum, 10.16 mHz/line.
Figure 9.28 Current zoom spectrum, 10.16 mHz/line.
Figure 9.29 Time domain current waveform.
Figure 9.30 Current zoom spectrum, baseband span 0–50 Hz, 12,800 lines, 3.9 mHz/line.
Figure 9.31 Time domain current.
Figure 9.32 Current zoom spectrum, baseband span 0–50 Hz, 12,800 lines, 3.9 mHz/line.
Figure 9.33 General layout of an ESP installation.
Figure 9.34 Current spectra recorded 4 months apart, baseband span 0–100 Hz, 12,800 line, 7.8 mHz/line.
Figure 9.35 Radial wear on the pump stage hubs and shaft/bushing. Reproduced with permission of EM Diagnostics Ltd.

Chapter 10

Figure 10.1 Idealized illustration of uniform airgaps “g” between magnets.
Figure 10.2 Idealized case of constant radial airgap “g”.
Figure 10.3 Schematic illustration of static airgap eccentricity only.
Figure 10.4 Schematic illustration of dynamic airgap eccentricity only.
Figure 10.5 Illustration of only static airgap eccentricity.
Figure 10.6 Measurement of radial airgap.
Figure 10.7 3-Phase 3300 V, 670 HP/500 kW, 110 A, 50 Hz, 593 r/min, 10-pole, p.f. = 0.85, efficiency = 93.6% SCIM. Rotor-to-stator rub and a consequential stator failure.
Figure 10.8 3-Phase, 4350 HP/3245 kW, 11 kV, 204 A, 50 Hz, 592 r/min, p.f. = 0.88, efficiency = 95% SCIM. Catastrophic rotor-to-stator rub and stator winding failure in a brand new SCIM, August 2004. A segmental laminated rotor core—radial movement of the rotor core.
Figure 10.9 3-Phase, 11,000 V, 109/86 A, 1610/1122 kW (2158/1500 HP), 594/495 r/min, 50 Hz, star connected, PAM SCIM. Catastrophic rotor-to-stator rub, FD fan motor.
Figure 10.10 Idealized illustration of rotor slotting ripple in current–time domain waveform.
Figure 10.11 Idealized current spectrum indicating the spectrum between 0 and 3000 Hz.
Figure 10.12 Idealized current zoom spectrum for the airgap eccentricity signature.
Figure 10.13 Current zoom spectrum around f_{rs( + 1)} for motor A, baseband span 70–1200 Hz, 12,800 lines, 88.3 mHz/line.
Figure 10.14 Current zoom spectrum around f_{rs( + 1)} for motor B, baseband span 70–1200 Hz, 12,800 lines, 88.3 mHz/line.

Chapter 11

Figure 11.1 Current zoom spectrum, baseband span 0–130 Hz, 12,800 lines, frequency resolution is 10.16 mHz/line.
Figure 11.2 Current spectrum, baseband span 70–1800 Hz, 12,800 spectral lines, frequency resolution is 0.135 Hz/line.
Figure 11.3 Current spectrum, baseband span 70–1800 Hz, 12,800 spectral lines, frequency resolution 0.134 Hz/line, f_{rs( + 1)} is identified as 1548.4 Hz, operating current was 70 A.
Figure 11.4 Current zoom spectrum showing f_{rs( + 1)}, f_{rs( − 1)}, and f_{rs( + 3)}, spaced 2f apart.
Figure 11.5 Current zoom spectrum around f_{rs( + 1)}, no ± f_r components around f_{rs( + 1)}.
Figure 11.5a An illustration of the position of f_{rs( + 1)} at a slip of 0.001 (0.1%).
Figure 11.6 Current zoom spectrum, motor A, f_{rs( + 1)} is 1488.5 Hz at –102 dB, operating current was 224 A.
Figure 11.7 Current zoom spectrum, motor B, f_{rs( + 1)} is 1487.7 Hz at –102 dB, operating current was 216 A.
Figure 11.8 (a) and (b) Photos of CW units. Reproduced with permission of EM Diagnostics Ltd.
Figure 11.8 CW1 current spectrum.
Figure 11.9 CW2 current spectrum.
Figure 11.10 CW3 current spectrum.
Figure 11.11 CW4 current spectrum.
Figure 11.12 CW1 current spectrum
Figure 11.13 CW2 current spectrum.
Figure 11.14 CW3 current spectrum.
Figure 11.15 CW4 current spectrum.
Figure 11.16 DE airgap measurements.
Figure 11.17 NDE airgap measurements.
Figure 11.18 DE airgap measurements.
Figure 11.19 DE airgap measurements.
Figure 11.20 Current spectrum after modifications to give 3% airgap eccentricity.
Figure 11.21 Motor A current zoom spectrum.
Figure 11.22 Motor A current zoom spectrum to display rotor slot passing frequencies.
Figure 11.23 Motor A current zoom spectrum to display ± f_r components around f_{rs( + 5)}.
Figure 11.24 Motor B current zoom spectrum to display ±f_r components around f_rs(+5).
Figure 11.25 DE airgaps.
Figure 11.26 NDE airgaps.
Figure 11.27 Motor A current zoom spectrum after airgap eccentricity was reduced to 10% with motor at ambient temperature and stationary.
Figure 11.28 Current zoom spectrum to measure the supply frequency at 60.064 Hz; frequency resolution of 0.01 Hz/line.
Figure 11.29 Current zoom spectrum to detect f_{rs( + 1)} and ± f_r components.
Figure 11.30 Stator core assembly showing coils have been removed from the slots.
Figure 11.31 Samples of severely damaged semi-conductive coatings due to mechanical forces and vibration enhanced by consequential slot discharges of the line end coils.
Figure 11.32 Current zoom spectrum to measure supply frequency.
Figure 11.33 Current zoom spectrum to measure f_{rs( + 1)} and to identify any ± f_r components around f_{rs(+ 1)}, uncoupled, no-load run.
Figure 11.34 Current zoom spectrum to measure f_{rs( + 1)} and to identify any ± f_r components around f_{rs( + 1)}, coupled run at 60 A (46% full-load current).
Figure 11.35a Time domain current waveform to the motor, note the shunt across the CT gives a voltage.
Figure 11.35b Current spectrum, baseband frequency 0—120 Hz, 12,800 spectral lines, frequency resolution 9.38 mHz/line.
Figure 11.36 Current spectrum 0–2500 Hz to show the higher harmonics relative to the inverter base frequency of 50.034 Hz.
Figure 11.37 Current zoom spectrum.
Figure 11.38 Motor being MCSA tested.
Figure 11.39 Current spectrum, 12,800 lines, 0–80 Hz, 6.25 mHz/line.
Figure 11.40 Current spectrum, 12,800 lines, 70–1800 Hz.
Figure 11.41 Current zoom spectrum, 12,800 lines in baseband span of 70–1800 Hz.
Figure 11.42 Annotated current zoom spectrum.
Figure 11.43 Filtered current spectrum, 60 Hz removed, baseband span 70–3000 Hz, 12,800 lines, 0.23 Hz/line.
Figure 11.44 Filtered current zoom spectrum to identify f_{rs( + 3)} and any ± f_r components.
Figure 11.45 Current spectrum, 12,800 line, 0–130 Hz, frequency resolution 0.01 Hz/line.
Figure 11.46 Filtered current spectrum, 70 to 1200 Hz, 12,800 lines, 0.883 Hz/line.
Figure 11.47 Filtered current spectrum, 70 to 1200 Hz, 12,800 lines, 0.883 Hz/line.
Figure 11.48 Current spectrum to display RSPF components.
Figure 11.49 Current spectrum 12,800 lines, 0 to 130 Hz, 0.01 Hz/line.
Figure 11.50 Filtered current spectrum 70 to 2800, 12,800 lines, 0.212 Hz/line.
Figure 11.51a Shows the odd and even harmonics up to the 20th supply harmonic.
Figure 11.51b This shows the odd and even harmonics from the 23rd up to 43rd supply harmonic.
Figure 11.52a Dotted lines give the positions of components which are close to the predicted values for f_{rs( + 1)} at the full-load slip as a function of R from table 11.3.
Figure 11.52b Dotted lines give the measured components for f_{rs( + 1)} at the full-load slip as a function of R from table 11.1.
Figure 11.53 Current zoom to display (f_{rs( − 1)}) and (f_{rs( + 1)}).
Figure 11.54 Current zoom to display f_{rs( + 1)} and any ± f_r components around it.
Figure 11.55 Airgap measurements via feeler gauges.
Figure 11.56 Airgap measurements via feeler gauges.
Figure 11.57 Current spectrum to measure the exact frequency of the supply.
Figure 11.58 Current spectrum, 70–2300 Hz.
Figure 11.59 Current zoom spectrum.
Figure 11.60 Current spectrum to measure the exact frequency of the supply.
Figure 11.61 Current spectrum, 70–3000 Hz.
Figure 11.62 Current zoom spectrum.

Chapter 12

Figure 12.1 Example of HV stator coil. Reproduced with permission of EM Diagnostics Ltd.
Figure 12.2 Example of adjacent HV stator coils to show the end winding region. Reproduced with permission of EM Diagnostics Ltd.
Figure 12.3 Sample cross-section of an 11kV coil. Reproduced with permission of EM Diagnostics Ltd.
Figure 12.4 Example of failure due to shorted turns in a 6.6 kV SCIM.
Figure 12.5 R-phase, current spectrum, no shorted turn. Source: Thomson (2001) [12.2]. Reproduced with permission of IEEE.
Figure 12.6 R-phase, current spectrum with the short circuit current limited to 3.6 times the full-load phase current. Source: Thomson (2001) [12.2]. Reproduced with permission of IEEE.
Figure 12.7 Y-phase, current spectrum with the short circuit current limited to 3.6 times the full-load phase current. Source: Thomson (2001) [12.2]. Reproduced with permission of IEEE.
Figure 12.8 B-phase, current spectrum with the short circuit current limited to 3.6 times the full-load phase current. Source: Thomson (2001) [12.2]. Reproduced with permission of IEEE.
Figure 12.9 Damaged coils due to direct shorted turns in one coil.
Figure 12.10 Line current spectrum with direct short circuited turns in a coil.
Figure 12.11 Schematic diagram to identify the component parts of a ball bearing.
Figure 12.12 Illustration of the contact angle, ball diameter and pitch diameter of a ball bearing.

George W. Arnold	Xiaoou Li	Ray Perez
Giancarlo Fortino	Vladimir Lumelsky	Linda Shafer
Dmitry Goldgof	Pui-In Mak	Zidong Wang
Ekram Hossain	Jeffrey Nanzer	MengChu Zhou

CURRENT SIGNATURE ANALYSIS FOR CONDITION MONITORING OF CAGE INDUCTION MOTORS

Industrial Application and Case Histories