IET ENERGY ENGINEERING SERIES 108

Fault Diagnosis ofInduction Motors

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Fault Diagnosis ofInduction MotorsJawad Faiz, Vahid Ghorbanian and Gojko Joksimović

The Institution of Engineering and Technology

Published by The Institution of Engineering and Technology, London, United Kingdom

The Institution of Engineering and Technology is registered as a Charity in England &Wales (no. 211014) and Scotland (no. SC038698).

† The Institution of Engineering and Technology 2017

First published 2017

This publication is copyright under the Berne Convention and the Universal CopyrightConvention. All rights reserved. Apart from any fair dealing for the purposes of researchor private study, or criticism or review, as permitted under the Copyright, Designs andPatents Act 1988, this publication may be reproduced, stored or transmitted, in anyform or by any means, only with the prior permission in writing of the publishers, or inthe case of reprographic reproduction in accordance with the terms of licences issuedby the Copyright Licensing Agency. Enquiries concerning reproduction outside thoseterms should be sent to the publisher at the undermentioned address:

The Institution of Engineering and TechnologyMichael Faraday HouseSix Hills Way, StevenageHerts, SG1 2AY, United Kingdom

www.theiet.org

While the authors and publisher believe that the information and guidance given in thiswork are correct, all parties must rely upon their own skill and judgement when makinguse of them. Neither the authors nor publisher assumes any liability to anyone for anyloss or damage caused by any error or omission in the work, whether such an error oromission is the result of negligence or any other cause. Any and all such liability isdisclaimed.

The moral rights of the authors to be identified as authors of this work have beenasserted by them in accordance with the Copyright, Designs and Patents Act 1988.

British Library Cataloguing in Publication DataA catalogue record for this product is available from the British Library

ISBN 978-1-78561-328-9 (hardback)ISBN 978-1-78561-329-6 (PDF)

Typeset in India by MPS LimitedPrinted in the UK by CPI Group (UK) Ltd, Croydon

Contents

Preface xiAbout the authors xv

1 Condition monitoring and fault diagnosis of induction motors 11.1 Introduction 1References 7

2 Theory of line-start and inverter-fed induction motors 112.1 Introduction 112.2 Induction motor structure 122.3 Line-start induction motor: linear and single harmonic model

of a healthy motor 182.3.1 Flux equation 222.3.2 Electromagnetic torque equation 28

2.4 Inverter-fed induction motors 402.4.1 Constant voltage per frequency strategy (CV/F) 402.4.2 Space vector modulation 442.4.3 Analysis of motor behavior in open-loop CV/F mode 482.4.4 Reference frame theory of induction motors 532.4.5 Field-oriented control of induction motors 562.4.6 Direct torque control of induction motors 59

References 67

3 Induction motor faults: basics, developments and laboratory-scaleimplementation 713.1 Introduction 713.2 Broken bar/end-ring fault in induction motors 74

3.2.1 Time-domain behavior of induction motors withbroken bar/end-ring faults 84

3.3 Eccentric/misaligned and bearing faults in induction motors 873.3.1 Misalignment inclined rotor 923.3.2 Theoretical analysis of eccentric induction motor 943.3.3 Bearing faults in induction motor 104

3.4 Short-circuit fault in induction motors 1053.5 Laboratory-sale implementation of induction motor faults 118

3.5.1 Three-phase induction motor 1193.5.2 Autotransformer 121

3.5.3 Drive 1213.5.4 Motor load 1253.5.5 Implementation of broken bar fault 1303.5.6 Implementation of eccentricity fault 1383.5.7 Implementation of interturn short-circuit fault 1403.5.8 Signals and sensors 1423.5.9 Data acquisition 1533.5.10 Overall scheme of the conventional cabled diagnosis

system implementation 1583.5.11 Wireless condition monitoring setup 160

References 163

4 Magneto-motive force waves in healthy three-phase inductionmotors 1694.1 Current sheet concept 1694.2 Winding function concept 176

4.2.1 Concentrated full-pitch coil MMF 1784.2.2 Distributed full-pitch phase winding 1824.2.3 Pulsating MMF 1844.2.4 Three-phase full-pitch (single-layer) winding 1884.2.5 Three-phase shorted-pitch coil (double-layer) winding 191

4.3 Rotating MMF wave—analytical approach 1974.4 Fractional slot winding 2004.5 Wound rotor MMF space harmonics 2024.6 Cage rotor MMF space harmonics 202References 207

5 Multiple-coupled circuit model of induction motors 2095.1 Model description 210

5.1.1 Electrical subsystem equations 2105.1.2 Mechanical subsystem equations 2115.1.3 Model parameters 212

5.2 Skewing of rotor bars 2195.3 Linear rise of MMF across slot 2215.4 Solution of mathematical model 226

5.4.1 Stator phase windings connection 2285.5 Modeling inductions motors with broken rotor bar(s)/end-ring(s) 2365.6 Modeling induction motors with air-gap eccentricity 239

5.6.1 Inductance calculation 2395.6.2 Static eccentricity 2405.6.3 Dynamic eccentricity 2435.6.4 Numerical model results 247

5.7 Modeling induction motors with interturn short circuitin stator winding 2495.7.1 Numerical model results 252

References 254

vi Fault diagnosis of induction motors

6 Finite element implementation of induction motors in healthyand faulty conditions 2576.1 Introduction 2576.2 Electromagnetic field equations 2596.3 Magnetic vector potential, magnetic scalar potential, current

vector potential 2626.4 ~T -F Formulation 2646.5 ~A–V Formulation 2656.6 Coupled magneto-static and eddy current-field problem 2666.7 Transient-with-motion formulation 2686.8 Finite element method 271

6.8.1 Material modeling 2726.8.2 Magnetic loss calculation 2766.8.3 Mesh generation 2786.8.4 Set-up system of equations 280

6.9 Induction motor examples 2866.9.1 Healthy motor operation 2906.9.2 Broken bar motor operation 2976.9.3 Eccentric motor operation 3006.9.4 Short-circuited motor operation 305

References 320

7 Signal-processing techniques utilized in fault diagnosis procedures 3257.1 Introduction 3257.2 Fourier transform 327

7.2.1 Recursive FFT algorithm in MATLAB 3317.2.2 Iterative FFT algorithm in MATLAB 3317.2.3 Example 331

7.3 Short-time Fourier transform 3387.4 Multiresolution analysis 3397.5 Wavelet transform 343

7.5.1 Resolution in time-frequency map 3437.6 Inverse wavelet transform 3467.7 Discrete of wavelet transform 3467.8 Hilbert–Huang transform 353References 366

8 Diagnosis of broken bars fault in induction motors 3678.1 Introduction 3678.2 Motor current signature analysis (MCSA) 3698.3 Pendulous oscillation 3748.4 Virtual current technique 3758.5 Air gap flux density 3768.6 Speed fluctuations 3778.7 Gyration radius 379

Contents vii

8.8 Time-domain analysis of nonadjacent broken bars fault 3818.9 Spectrum of motor current 3858.10 Effect of closed loops on faulty motor signals 3938.11 Analytical analysis of the effect of speed variation on sideband

components 3988.12 Motor power spectrum 4018.13 Additional frequency-domain fault indices 4048.14 Motor transient operation 4058.15 Application of wavelet transform to the diagnosis of broken

bars fault 4078.16 Application of Hilbert–Huang transform to the diagnosis

of broken bars fault 4098.17 Loss characterization of induction motors with broken bars fault 4168.18 Conclusion 419References 420

9 Diagnosis of eccentricity fault in induction motors 4319.1 Introduction 4319.2 Effect of mixed eccentricity fault on time-domain variation

of speed and torque signals 4329.3 Normalized splitting severity factor 4339.4 Ratio of area enclosed by stator current in two consecutive

cycles to average area of two stator current cycles 4359.5 High-frequency components of stator current 4389.6 Low-frequency components of stator current 4429.7 Joint analysis of low- and high-frequency patterns of

stator current 4489.8 Low-frequency components of voltage space vector and

high-frequency components of current space vector 4499.9 The ratio of sum of right (high) and left (low) sideband

components to no-load current 4519.10 Negative sequence current 4579.11 Harmonic components of instantaneous power 4649.12 Loss characterization of induction motors with eccentricity fault 467References 467

10 Diagnosis of interturn short-circuit fault in induction motors 47310.1 Motor current signature analysis 47310.2 Healthy cage rotor induction motor 474

10.2.1 MMF space harmonics 47410.2.2 Slot permeance harmonics 47810.2.3 Saturation permeance harmonics 480

10.3 MCSA of an induction motor with interturn fault 486

viii Fault diagnosis of induction motors

10.4 A review of interturn short-circuit fault detection techniquesfor induction motors 497

10.5 MCSA of wound-rotor induction motor 502References 505

Index 509

Contents ix

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Preface

Induction machines are used more extensively than any other form of electricalmachines. Low voltage machines are often used in domestic applications. How-ever, larger induction machines with higher power and voltage ratings are widelylaunched in industrial environment such as pumps, mines, petrochemical andelectrical power generators in order to provide motive force for major services.Nowadays, the responsibilities of induction machines are continuously growing,and the reliable operation of induction machines is strategically very important forproviding essential services.

There are many faults which can prevent smooth operation of inductionmachines. Generally, any fault starts as a small declination from the healthy normaloperation. Then, it may lead to a catastrophic failure if the fault is not detected andtreated at its early stages. Therefore, a concept called ‘‘condition monitoring’’ ofinduction motors is introduced. Condition monitoring is a process of detecting anddiagnosing fault-related changes of an essential motor quantity. Such action allowsto schedule a proper maintenance, prevents failure, avoid significant damages,avoid economic lost, stop outages, optimizes the performance and enhances thequality control.

This book originated from the experience of the authors during researchingfault diagnosis of induction machines at University of Tehran, Iran and Universityof Montenegro, Podgorica, Montenegro. Our research has led to many publicationsin induction machine fault detection, some have been referred in the book. Thisbook is intended to help electrical engineers in industries and postgraduate/graduatestudents who would like to do research in this area or similar topics. Moreover, thisbook in an endeavor to collect recent attempts in the field of diagnosis of inductionmotors and sort them in a meaningful way so that potential readers can find ahierarchical discussion on different types of faults. This includes basics, develop-ments, simulation approaches and experimental measurement of three importanttype of faults, namely the broken bars, eccentricity and interturn faults.

The book has been managed to cover fundamental and advanced aspects of thepreviously mentioned types of faults by providing step-by-step theoretical, analy-tical, numerical and experimental implementations. Basically, there are ten chap-ters as follows:

Chapter 1 provides a preliminary discussion on different types of faults and thecorresponding influential factors in induction machines. Then, the necessity of thefault diagnosis procedures and their importance in maintaining a safe industrialenvironment are highlighted.

Chapter 2 explains the fundamentals of motor-drive operations in differentsupply modes including the line-start and inverter-fed applications in order toprepare readers for the next chapters.

Chapter 3 is probably the heart of this book since it provides a fundamental toadvance knowledge of different types of faults, namely the broken bars, eccen-tricity and short-circuit faults. Moreover, a useful implementation technique ofdifferent faults and the corresponding measurement are discussed.

Chapter 4 addresses detailed analytical analysis of healthy induction motors.This chapter is considered as the basis for analyzing the time and space harmonicsof induction motors, which will be used to extract fault indicators in the next partsof the book.

Chapter 5: The winding function theory is one of the most useful analyticalmodeling approaches of different types of faults in induction motors, which isexplained in this chapter. The broken bars, eccentricity and short-circuit faults willbe formulated using the winding function theory and some typical results of thecorresponding simulation process are introduced.

Chapter 6: As the most reliable simulation process of electrical machines andtheir defects, the finite element method is targeted in Chapter 6. The mathematicalimplementation of the approach is provided first. Then, the way to implementdifferent types of faults is discussed.

Chapter 7: Time, frequency and time-frequency signal processing techniquesare explained and the corresponding MATLAB codes are provided in Chapter 7 sothat one can easily use the programs to conduct further signal processing applied todifferent signals of faulty motor.

Chapter 8: The broken bars fault is the main focus of Chapter 8. In this chapter,various aspects of the corresponding diagnosis process are provided in order to geta better realization of how the broken bars fault is detected and diagnosed in dif-ferent operating conditions. Different drive systems, various load levels, variousspeed levels and different indicators are addressed.

Chapter 9: The same process as that of Chapter 8 is followed in Chapter 9 inorder to address the issues related to the eccentricity fault. Two main types of faultsincluding the static and dynamic eccentricity faults are investigated by means oftime and frequency analysis.

Chapter 10: The short-circuit fault will be studied in Chapter 10. Different timeand frequency domain techniques will be used to address the challenges related todiagnosis of the short-circuit fault. Two types of machines, namely the wound andsquirrel-cage induction motors, are investigated.

So many postgraduate/graduate students have helped with the preparation ofthe present book that we cannot properly acknowledge them all and this bookwould never have been possible without their excellent research over the last15 years. We would specially like to thank University of Tehran for its previousfinancial supports of the projects whose outcome has been gathered here as a book.

We would like to thank Mrs. Rana Hassanpour Bradaran (M.Sc. in Englishlanguage translation) for her efforts to edit and improve the language of the book,Dr. Iman Tabatabaei Ardekani, previous M.Sc. student in the University of Tehran

xii Fault diagnosis of induction motors

and now senior lecturer in Unitec Institute of Technology, Auckland, New Zealand,Dr. Bashir Mahdi Ebrahimi the previous Ph.D. student in the University of Tehranand now the director in Pars Generator Company in Iran, Dr. Mansour Ojaghi theprevious Ph.D. student in the University of Tehran and now Associate Professor inUniversity of Zanjan, Iran, the previous M.Sc. students Amir Masoud Takbash,Mr. Mahmoud Ghasemi-Bijan and Mr. Mehran Keravand in the University ofTehran.

Preface xiii

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About the authors

Jawad Faiz is Professor in the School of Electrical and Computer Engineeringat the University of Tehran, Iran. His research interests are the design, modelingand fault diagnosis of electrical machines and transformers. He is a member ofthe Iran Academy of Sciences and has published more than 460 papers and a bookin this field.

Vahid Ghorbanian received his PhD degree in Electrical Engineering fromMcGill University, Montreal, Canada in 2017. His research interests includeanalysis, design, optimization, condition monitoring and fault diagnosis of con-ventional and new types of line-start and inverter-fed electrical machines. He isa recipient of the McGill Engineering Doctoral Awards (MEDA) in 2013.

Gojko Joksimovic is Professor of Electrical Power Engineering at the Universityof Montenegro, Montenegro. His research interests are in electrical machines, theirdesign, analysis and modeling. He has a long research record on the modeling andfault detection of induction machines. He is a recipient of the prestigious Alexandervon Humboldt research fellowship. He is a senior member of IEEE.

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