Fault Diagnosis of Induction Motors
2: Department of Electrical and Computer Engineering, McGill University, Montreal, QC, Canada
3: Faculty of Electrical Engineering, University of Montenegro, Podgorica, Montenegro
Induction motors are still among the most reliable and important electrical machines. The wide range of their use involves various electrical, magnetic, thermal and mechanical stresses which results in the need for fault diagnosis as part of the maintenance. A yet unreached goal is the development of a generalized, practical approach enabling industry to accurately diagnose different potential induction motor faults. Fault Diagnosis of Induction Motors aims to fill this gap by focusing on theoretical, experimental and computer aided processes for fault diagnosis, building a comprehensive, structural approach allowing users to select the proper diagnosis strategy. Topics covered include condition monitoring and fault diagnosis of induction motors; the theory of line-start and inverter-fed induction motors; induction motor faults basics, developments and laboratory-scale implementation; magneto-motive force waves in healthy three-phase induction motors; multiple coupled circuit model of induction motors; finite element implementation of induction motors in healthy and faulty conditions; signal processing techniques utilized in fault diagnosis procedures; diagnosis of broken bars fault in induction motors; diagnosis of eccentricity fault in induction motors; and diagnosis of inter-turn short circuit fault in induction motors. This work is essential reading for researchers and technicians involved with motor-drive applications and their related maintenance procedures or dealing with applications of signal processing techniques.
Inspec keywords: condition monitoring; signal processing; finite element analysis; induction motors; invertors; fault diagnosis
Other keywords: broken bar fault diagnosis; line-start theory; multiplecoupled circuit model; inverter-fed induction motors; condition monitoring; magnetomotive force wave; eccentricity fault diagnosis; signal processing technique; finite element implementation
Subjects: Signal processing and detection; Finite element analysis; General electrical engineering topics; DC-AC power convertors (invertors); Asynchronous machines
- Book DOI: 10.1049/PBPO108E
- Chapter DOI: 10.1049/PBPO108E
- ISBN: 9781785613289
- e-ISBN: 9781785613296
- Page count: 536
- Format: PDF
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Front Matter
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1 Condition monitoring and fault diagnosis of induction motors
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Electrical machines are one of the most growingly manufactured devices which are widely used not only in industries but also in domestic applications. Due to their higher efficiency level, they are common sources of electromechanical energy conversion. Various applications including control, automotive and power generation applications are served by means of these devices, and no one can deny their ability in being precisely controlled in terms of position, speed and torque which are some of the essential quantities in electromechanical devices.
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2 Theory of line-start and inverter-fed induction motors
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Induction motors, which hire fundamental rules of electromagnetism in order to produce rotational or translational mechanical movement when supplied by an input electric power, are energy conversion apparatus. These electromechanical devices are very well known for their smoothly run capability if a balanced input power supply, along with a symmetric motor structure, is used simultaneously. This is the reason why a balanced and symmetric three-phase motor supply system is usually preferred in industry due to its gentle and low noise. However, a higher number of phases, despite its rather higher topological complexity, are also possible. Notably, the underlying idea of the operation of this kind of motor is basically not related to different possible structures used in various applications. It quite depends on the nature of the induction phenomenon which couples the stator and rotor magnetic fields. Regardless of the stator geometry, there are generally two types of induction motors as the following: wound rotor, squirrel cage rotor. Generally speaking, the healthy motor behavior in the “line-start”supply mode is targeted. Therefore, readers could potentially follow up future details in terms of more complex operations such as inverter-fed applications. Otherwise, the advanced topics might be of a little bit vague if one does not have the proper background knowledge. All the motor-drive principles required for a better realization of motor behavior are investigated as well. As the starting point, the physical structure of the motor is first illustrated and analyzed in the following section.
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3 Induction motor faults: basics, developments and laboratory-scale implementation
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A brief overview of the current chapter reveals the attempts to understand the fundamentals of fault occurrence and the way how fault affects the motor timedomain behavior. The attempts were totally devoted to explain the theoretical fault basis and consequently address the most significant time-domain variations by means of which a fault might probably be detected. Nevertheless, not all faults introduce a specifically detectable behavior, at least in a time domain. A step-bystep laboratory-scale implementation of various types of faults, along with the required details, was provided. By means of this knowledge, a simple but very useful setup of fault diagnosis based on which one can study different fault aspects is indeed achieved.
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4 Magneto-motive force waves in healthy three-phase induction motors
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Alternating current (ac) windings in electrical machines basically have a twofold purpose. In electrical generators ac windings are place where electromotive force (EMF) should be induced. In electrical motors, primarily ac windings goal is to produce rotating magneto-motive force (MMF) wave. In any case, ac windings should be designed in such a manner that induced EMF or generated rotating MMF wave consists predominantly of the fundamental sinusoidal component. Therefore, the starting point of an induction machine study is the analysis of MMF waves in the air gap of such machines. This assumes knowledge of winding distribution along the air gap from stator as well as from rotor side. The magnetic flux is analogous to the electric current. The MMF which sets up the magnetic flux is analogous to the EMF. The MMF is equivalent to a number of turns of wire carrying an electric current. If either the current through a coil (as in an electromagnet) or the number of turns of wire in the coil is increased, the MMF will be higher; and if the rest of the magnetic circuit remains the same, the magnetic flux increases proportionally [1]. At least two different approaches exist for describing winding distribution.
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5 Multiple-coupled circuit model of induction motors
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There are a lot of different mathematical models which enable the analysis of an induction machine. Generally, they could be divided into static and dynamic models. Static models allow the analysis of static characteristics of induction motors. This model, for example, is the well-known single-phase equivalent circuit of induction motor. Dynamic models can provide time variations of motor currents, developed electromagnetic torque and rotor speed as outputs. Such models enable the analysis of induction machines in transient modes.
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6 Finite element implementation of induction motors in healthy and faulty conditions
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The following are included in this chapter: a comprehensive formulation of the Maxwell's equations; the finite element formulations; an efficient approach to the implementation of broken bar, eccentricity and short-circuit faults in an FEM package; a discussion of the adjustments in terms of selecting a proper time step and mesh size for simulations; the inclusion of a magnetic field analysis of induction motors by providing two examples, a cage and a wound rotor (the dimensions and materials are also provided so that readers might implement the same models in their own packages); and the study of the flux density variations in different faulty conditions and various motor parts including the stator yoke, the stator teeth, the air gap, the rotor teeth and the rotor back-iron.
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7 Signal-processing techniques utilized in fault diagnosis procedures
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Signal processing is a widely used technology that pervades every aspect of our lives which are actually unknown to many. This chapter surveys some basic concepts which drive the field and focuses on the other two types of analyses, i.e., the frequency- and time-frequency analyses. First, the mathematical concepts are explained; then MATLAB implementation of transforms, along with intuitive examples, is provided in order to address the corresponding technical issues during the implementation and postprocessing analysis.
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8 Diagnosis of broken bars fault in induction motors
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Having discussed the fundamentals of induction motors with broken bars fault and explained how the breakage affects the motor electromagnetic and mechanical properties, the diagnosis approaches and the fault indices are going to be discussed in detail with the purpose of introducing a comprehensive diagnosis process. There are also other specifications of the diagnosis approaches which will be introduced and explained in this chapter.
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9 Diagnosis of eccentricity fault in induction motors
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The following aspects will be comprehensively discussed in present chapter: to introduce the eccentricity-related indices in time, frequency and time-frequency domains commonly used in condition monitoring of induction motors; to investigate the effect of motor loading; to investigate the effect of various supply modes; to investigate various fault severities and types; to characterize faulty motor losses; and to provide more technical aspects of the diagnosis process of eccentricity fault which might affect the diagnosis process.
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10 Diagnosis of interturn short-circuit fault in induction motors
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Motor current signature analysis (MCSA) is one of the most powerful methods of online motor diagnosis for detecting motor faults. MCSA technique in case of cage rotor induction motors means the analysis of stator-line current spectrum obtained by applying Fourier transform to the stator current waveform in steady-state conditions. The stator-line current frequency spectrum represents, a sort of speaking, an electrocardiogram of an electrical machine. This technique is particularly useful because it is noninvasive, and the search coil is the stator winding of the machine, itself. Using MCSA has advantages such as no estimation of motor parameters and the simplicity of current sensors and their installation.
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Back Matter
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