Static Eccentricity Fault Research Articles

The Zero-Sequence Current as a Generalized Diagnostic Mean in Δ-Connected Three-Phase Induction Motors

In this paper, a new diagnostic mean is introduced for accurate, reliable, and effective diagnosis of faults in delta-connected induction motors. This mean is the zero-sequence stator current spectrum. The study is carried out with analytical calculations and finite-element method simulations. Most common faults are examined for a 4-kW cage induction motor. The analysis will reveal that the proposed mean is able to successfully identify the static eccentricity fault, even in induction motors which produce principal slot harmonics, the broken bar fault, the unbalanced voltage supply, and the stator interturn short-circuit. It will also be shown that through the proposed method, it is possible to distinguish the interturn short-circuit from the unbalanced voltage supply.

Static Eccentricity Fault Recognition in Three-Phase Line Start Permanent Magnet Synchronous Motor Using Finite Element Method

This paper is dedicated to investigating static eccentricity in a three-phase LSPMSM. The modeling of LSPMSM with static eccentricity between stator and rotor is developed using finite element method (FEM). The analytical expression for the permeance and flux components of nonuniform air-gap due to static eccentricity fault is discussed. Various indexes for static eccentricity detection using stator current signal of IM and permanent magnet synchronous motor (PMSM) are presented. Since LSPMSM is composed of a rotor which is a combination of these two motors, the ability of these features is evaluated for static eccentricity diagnosis in LSPMSM. The simulated stator current signal of LSPMSM in the presence of static eccentricity is analyzed in frequency domain using power spectral density (PSD). It is demonstrated that static eccentricity fault generates a series of low frequency harmonic components in the form of sidebands around the fundamental frequency. Moreover, the amplitudes of these components increase in proportion to the fault severity. According to the mentioned observations, an accurate frequency pattern is specified for static eccentricity detection in three-phase LSPMSM.

A Novel and Effective Method of Static Eccentricity Diagnosis in Three-Phase PSH Induction Motors

Eccentricity-related faults are very common in induction motors and that is the reason for the extensive and worldwide research on their prompt diagnosis during the past decades. Previous works have shown that traditional diagnostic methods cannot offer reliable results for principal slot harmonics (PSH) induction motors. Moreover, most works were focused in the detection of dynamic and mixed, rather than static eccentricity. This paper is focused on the detection of the static eccentricity fault and its severity in PSH induction motors. The proposed method is original and proves to be reliable for the static eccentricity fault detection, even when the severity of the fault is low. The work was carried out with both finite element method (FEM) simulations and experimental testing.

Static eccentricity fault diagnosis using the signatures analysis of stator current and air gap magnetic flux by finite element method in saturated induction motors

Static eccentricity produces low frequency air gap flux components, however they can be observed in stator current spectrum only under mixed eccentricity, and for high degrees of rotor shifting. Unlike motor current signature analysis, the air-gap magnetic flux signature analysis allows to detect small degree of purely static eccentricity. The simulation results are obtained by using time stepping finite elements method. In order to indicate the influence of the magnetic saturation upon the analysis of the faulty induction motor, two constant and non-liner permeability; are included in this paper. It is shown that the fault index amplitudes of obtained signals from the constant permeability are larger than that of the real case. In this paper the amplitudes of characteristic frequency components $$ f_{ecc} = \left| {f_{s} \pm k{\kern 1pt} f_{r} } \right| $$ with low degrees of purely static eccentricity fault are detected using air-gap magnetic flux signature analysis. Moreover, new index signatures are detected around the third time harmonics in air-gap magnetic flux density spectrum for saturated motor, those components are expressed by $$ f_{ecc} = mf_{s} \pm f_{r} $$ .

Detection of Eccentricity in Squirrel Cage Induction Motors by Finite Element Method

Finite Element method is used in this research work to detect eccentricity fault in squirrel cage induction motors. This paper is about the results obtained from the simulation part of the research on a real size motor. The simulation was done using FLUX software, which can solve the magnetizing partial differential equations of the rotor, stator and the air-gap by FEMM. In the primary stage of this research the focus is on two dimension mapping of the electromagnetic field of the motor by using FLUX-2D. The presented results in this paper show the effect of the eccentricity is traceable from the FEMM of the motor. At the later part of this paper, the results from the simulation part were tested against the analytical method for validation. In the analytical method the present research was concentrated on the stator current and sees how the original sinusoidal current signal is distorted after fault. At the final part of the paper a complete FFT analysis of the current and voltage were presented for two cases of static and dynamic eccentricity faults. The paper is concluded by showing the effectiveness of this research for eccentricity fault diagnoses.

Static Eccentricity Fault Detection in Single-Stator–Single-Rotor Axial-Flux Permanent-Magnet Machines

This paper studies static eccentricity (SE) fault detection in axial-flux permanent-magnet (AFPM) machines using 3-D finite-element analysis. The use of numerical modeling makes it possible to precisely study the eccentricity fault detection in these types of machines. The simulations are validated using experimental measurements. To the best knowledge of the authors, SE fault detection in AFPMs has not been studied before. Hence, a new definition for the SE factor is presented in these types of machines. A motor with different degrees of rotor eccentricity is simulated, and the back electromotive force (EMF) of all coils of the stator is obtained. In addition, an appropriate criterion has been presented for the fault detection using the back EMF of the coils. This study indicates that the back EMF of the coils of the stator is a good criterion for eccentricity fault detection. It is observed that the unbalanced back EMF suggests a method for the indirect measurement of eccentricity that could be carried out during manufacturing and assembling processes or maintenance operation.

Static, Dynamic, and Mixed Eccentricity Faults Diagnosis in Switched Reluctance Motors Using Transient Finite Element Method and Experiments

This paper presents a new method for noninvasive diagnosis of static, dynamic, and mixed eccentricity faults in switched reluctance motors (SRMs). This method makes it possible to precisely determine the eccentricity fault features. The proposed signature in this algorithm is based on the analysis of produced current with a particular variation pattern. It is theoretically shown that the occurrence and growth of the fault level cause an increase in amplitude of the produced current signature (PCS), which can be employed to diagnose the fault and extract its details. In this method, first, occurrence of the fault and its location are detected by utilizing eccentricity level detection pattern. Afterward, a new index to precisely determine the fault level is introduced. Then, a novel strategy based on the proposed pattern and index is offered to detect the type of eccentricity as well as the exact location of the faulty phase. For this purpose, an SRM under eccentricity fault is modeled using three dimensional transient finite element method (TFEM). This precise model considers all complex motor geometry, nonlinear characteristics of the motor, end effects and axial fringing effects. A test bed in the laboratory is established to perform various measurements on the eccentric motor with different fault levels. The experimental results validate the numerical analysis outcomes. Fault detection and analysis in SRM demonstrate that the algorithm presented can assure the reliability of detection as well as the sensitivity of eccentricity fault in a SRM.

Detection of a static eccentricity fault in a closed loop driven induction motor by using the angular domain order tracking analysis method

In this study, a new method was presented for the detection of a static eccentricity fault in a closed loop operating induction motor driven by inverter. Contrary to the motors supplied by the line, if the speed and load, and therefore the amplitude and frequency, of the current constantly change then this also causes a continuous change in the location of fault harmonics in the frequency spectrum. Angular Domain Order Tracking analysis (AD-OT) is one of the most frequently used fault diagnosis methods in the monitoring of rotating machines and the analysis of dynamic vibration signals. In the presented experimental study, motor phase current and rotor speed were monitored at various speeds and load levels with a healthy and static eccentricity fault in the closed loop driven induction motor with vector control. The AD-OT method was applied to the motor current and the results were compared with the traditional FFT and Fourier Transform based Order Tracking (FT-OT) methods. The experimental results demonstrate that AD-OT method is more efficient than the FFT and FT-OT methods for fault diagnosis, especially while the motor is operating run-up and run-down. Also the AD-OT does not incur any additional cost for the user because in inverter driven systems, current and speed sensor coexist in the system. The main innovative parts of this study are that AD-OT method was implemented on the motor current signal for the first time.

Diagnosis and Magnetic Field Analysis of Small Power Salient-Pole Synchronous Generator with Static Eccentricity Using Time-Stepping Finite-Element Method

This article presents a numerical simulation model for small power salient-pole synchronous generator under static eccentricity fault at no-load and full-load conditions using the two-dimensional time-stepping finite-element method. The influence of different degrees of the eccentricity fault on generator performances is described. Magnetic flux distribution within the generator, air gap flux density patterns under rotor poles shoe, and self- and mutual-inductances characteristics of the stator phases and rotor winding in both healthy and faulty conditions are determined. Fourier analysis of the air gap flux density under rotor pole shoes and no-load voltage profile is used to determine of the harmonic contents in the presence of the static eccentricity fault. In addition, spectrum analysis of the stator current is illustrated for on-line diagnosis of the static eccentricity fault. It shows that at the no-load condition with low excitation current, the effect of the eccentricity fault is considerable compared to that of the rated excitation current. It also shows that the presence of significant harmonics in the stator line current of faulty synchronous generators is dependent mainly on the generator design parameters. This will be proven by experimental and numerical results.

Pattern identification for eccentricity fault diagnosis in permanent magnet synchronous motors using stator current monitoring

A novel theoretical scrutiny is presented here, which extracts eccentricity fault signatures by monitoring the stator current in permanent magnet synchronous motors (PMSMs). In this analysis, effects of the stator slots and saturation are taken into account for static and dynamic eccentricity fault detection. Eccentricity signatures are utilised to introduce a particular frequency pattern, and amplitude of side-band components at proposed frequencies is employed as a proper index for eccentricity fault recognition. Competence of the nominated index to detect eccentricity, its type and its degree is investigated in faulty PMSM with different load levels. Hence, time-stepping finite-element method is used to model faulty PMSM and calculate stator currents for processing and obtaining aforementioned proposed index. The relation between the nominated index, static and dynamic eccentricity degrees is determined by a mutual information criterion. So, a white Gaussian noise is added to the simulated current and robustness of the proposed index is analysed with respect to the noise variance. Finally, the type and the degree of eccentricity are predicted using support vector machine as a classifier. The classification results indicate that the proposed features can estimate the eccentricity degree and its type. The simulation results are verified by the experimental results.

Detection of static eccentricity for permanent magnet synchronous motors using the coherence analysis

This paper reports on work to detect the static eccentricity faults for permanent magnet synchronous motor (PMSM) using spectral analysis methods. Measurements are carried out by collecting the stator current and voltage, torque and speed for healthy and faulty cases of the motor. Static eccentricity case is formed by changing the rotor position in the manner of sliding the shaft on a horizontal axis. As a result of the spectral analysis for the motor currents, side band effects appeared at around the fundamental frequency are determined as a most important indicator of the eccentricity. In addition to this determination, the eccentricity problem is observed from the torque and rotor speed data comparing with each others as well as current and voltage variations.

Effect of Magnetic Saturation on Static and Mixed Eccentricity Fault Diagnosis in Induction Motor

We have investigated the effect of magnetic saturation of core materials on the diagnosis of static and mixed-eccentricity faults in induction motors. We modeled the faults by using a modified winding function (MWF) and time-stepping finite-element (TSFE) methods to compute the stator currents of both healthy and faulty motors for processing. We then analyzed the stator signal spectra of the motors by the MWF and TSFE methods and estimated the amplitudes of sideband components attributable to the faults. The results obtained by TSFE agreed well with experimental measurements. However, there was considerable discrepancy between the MWF results and the experimental measurements. We investigated the reason for the discrepancy by analyzing the air gap magnetic field distribution in both healthy and faulty induction motors in order to determine their linear and actual magnetization characteristics. We found that, in a faulty motor, for fixed permeability, the analytic method yields a much larger magnetic flux amplitude than is actually the case. At the same time, the distribution of magnetic flux in the air gap is more asymmetric than the actual case. Here, we present our experimental results and those obtained with the MWF method, using the finite-element analysis package Opera2d 10.5, for two three-phase, four-pole, 60-Hz, 3-hp motors having 36 stator slots and 44 and 28 rotor slots, respectively.

Static Eccentricity Fault Diagnosis in Permanent Magnet Synchronous Motor Using Time Stepping Finite Element Method

This paper introduces a new index for noninvasive diagnosis of static eccentricity in permanent magnet synchronous motors (PMSM). Use of this index makes it also possible to precisely determine the eccentricity degree. The index is the amplitude of the harmonic components with a particular frequency pattern. Occurrence and increase of the fault degree cause the rise of amplitude of the harmonic components which can be used to diagnose the fault and determine its degree. To evaluate the ability of the proposed index for static eccentricity detection and estimation of its severity, the correlation between index and eccentricity degree is calculated. Then a three-layer artificial neural network is employed to classify the current and torque profiles to one of the four possible classes of eccentricities. After all, a white Gaussian noise is added to the both measured current and torque and robustness of the proposed index is analyzed with respect to the noise variance. A PMSM under static eccentricity fault is modeled using time stepping finite element method. This modeling includes all geometrical and physical characteristics of the machine components, non-uniform permeance of the air gap and non-uniform characteristics of the PM material. Use of this precise modeling makes it possible to access the demanded signals for a very high precision processing.

STATIC ECCENTRICITY FAULT DIAGNOSIS IN AN ACCELERATING NO-LOAD THREE-PHASE SATURATED SQUIRREL-CAGE INDUCTION MOTOR

A no-load induction motor under static eccentricity is modeled using time stepping finite element (TSFE) method; current, torque, and speed signals of the motor are obtained by finite element method (FEM) and used for static eccentricity fault diagnosis and analysis. The frequency spectrum analysis of the stator current around fundamental frequency component is used to predict the static eccentricity. Noise, unbalanced magnetic pull (UMP) and arc occur during the starting of the faulty motor, therefore, performance of the motor over the period of starting up to the steady-state is investigated. It is shown that the rate of obtained signals from the constant permeability based analysis is very larger than that of the real case. It is indicated that in order to obtain accurate results the saturation must be taken into account in the analysis of the motor. Simulation results for a 3 hp, three-phase, 230 V, 36 stator slots induction motor with 28 rotor slots are given in this paper. Experimental results for the motor confirm the simulation results very well.

Finite Element Transient Analysis of an On-Load Three-Phase Squirrel-Cage Induction Motor with Static Eccentricity

This paper presents the static eccentricity fault diagnosis using time stepping finite element (TSFE) method. In the previous publications on induction motor fault diagnosis by a finite-element method (FEM), steady-state analysis was proposed. White noise, large unbalanced magnetic pull (UMP), and even arc appear during the starting of a faulty induction motor. These phenomena particularly for large induction motor which have longer starting time are very important. In this paper, transient analysis of induction motor under fault is presented. In addition to the static eccentricity fault diagnosis, torque and speed due to the fault are also investigated. In order to show the significant effect of saturation on a faulty induction motor, simulations are carried out for a core with a constant permeability. The results of applying TSFE method and those obtained by application of winding function (WF) theory are compared.

Finite-element analysis of a switched reluctance motor under static eccentricity fault

This paper describes a two-dimensional finite-element analysis of an 8/6 switched reluctance motor with static eccentricity. It describes the influence of the eccentricity on the static characteristics of the motor and shows how to obtain flux lines, flux density distribution, and the flux-linkage/rotor angular position characteristic of the motor in both healthy and faulty conditions, as well as the static torque profiles of phases for different degrees of eccentricity. It shows that, at low current, the effect of the eccentricity is considerable compared to that at the rated current. Fourier analysis of the torque profile is used to study the variations of static torque harmonic contents.

Generator vibration fault diagnosis method based on rotor vibration and stator winding parallel branches circulating current characteristics

Rotor vibration characteristics are first analyzed, which are that the rotor vibration of fundamental frequency will increase due to rotor winding inter-turn short circuit fault, air-gap dynamic eccentricity fault, or imbalance fault, and the vibration of the second frequency will increase when the air-gap static eccentricity fault occurs. Next, the characteristics of the stator winding parallel branches circulating current are analyzed, which are that the second harmonics circulating current will increase when the rotor winding inter-turn short circuit fault occurs, and the fundamental circulating current will increase when the air-gap eccentricity fault occurs, neither being strongly affected by the imbalance fault. Considering the differences of the rotor vibration and circulating current characteristics caused by different rotor faults, a method of generator vibration fault diagnosis, based on rotor vibration and circulating current characteristics, is developed. Finally, the rotor vibration and circulating current of a type SDF-9 generator is measured in the laboratory to verify the theoretical analysis presented above.