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This paper introduces a novel index for static eccentricity (SE) fault diagnosis in synchronous reluctance motors (SynRMs). Although SynRMs with rotor barriers under SE have been modeled in a few papers, any indices for the fault detection have not yet been reported. The proposed index is a specific frequency pattern in the motor current, which can also determine the fault severity. A novel analytical magnetic field investigation is applied to ascertain the proposed index. An accurate nonlinear numerical method is proposed for the motor inductances calculation. The model considers the rotor flux barriers, magnetic saturation, and the stator slots effect. The air gap flux density and the motor current are then achieved. The fast Fourier transform is exploited as a signal-processing tool to calculate motor current spectra. Then, a two-dimension time-stepping finite element method is used to attest of the proposed numerical model. Effectiveness of the proposed index is verified by simulation and experimental tests. [ABSTRACT FROM AUTHOR]

In this paper, we develop a method for the estimation of airgap spatial variation from the harmonics that appear in the stator's current under static eccentricity conditions. We move beyond the detection of the eccentricity fault and endeavour to quantify the severity of this fault. To achieve this, we formulate the problem as a mathematical inverse problem and attempt to solve it in the Bayesian framework using the so-called Bayesian approximation error approach. The solution takes the form of an algorithm capable of estimating the parameter(s) that characterize the spatial variation of the airgap length from noisy and limited data. Furthermore, it can quantify the uncertainty associated with the results as a byproduct of the Bayesian analysis approach employed in this paper. The results demonstrate that with each iteration of the algorithm, estimation accuracy improves, and the uncertainty of the estimated results reduces. • Bayesian approximation error analysis shows promise in monitoring electrical machines with eccentric rotors. • The paper applies Bayesian inversion for online estimation of airgap length in induction machines with eccentric rotors. • The study estimates static eccentricity ratio from limited data on harmonics of the machine line currents. • This paper gives an analytical method for calculating all inductances of induction machines under static eccentricity. [ABSTRACT FROM AUTHOR]

Fault diagnosis and condition monitoring of synchronous machines running under load is a key determinant of their lifespan and performance. Faults such as broken rotor bars, bent shafts and bearing issues lead to eccentricity faults. These faults if not monitored may lead to repair, replacement and unforeseen loss of income. Researchers who attempted to investigate this kind of machine stopped at characterizing and deduced ways, types and effects of rotor eccentricity fault on the machine inductances using the winding function method. A modified closed-form analytical model of an eccentric synchronus reluctance motor (SynRM) is developed here taking into cognizance the machine dimensions and winding distribution for the cases of a healthy and unhealthy SynRM. This paper reports the study the SynRM under static rotor eccentricity using the developed analytical model and firming up the model with finite element method (FEM) solutions. These methods are beneficial as they investigated and presented the influence of the degrees of static eccentricity on the machine performance indicators such as speed, torque and the stator current and assess the extent to which the machine performance will deteriorate when running with and without load. The results show that static eccentricity significantly affects the machine's performance as the degree of eccentricity increases. [ABSTRACT FROM AUTHOR]

Permanent magnet vernier generators (PMVGs) are suitable for meeting power concussion requirements of traffic enforcement cameras and traffic‐driven applications. In this study, the performance of PMVGs at no‐load and full‐load are analysed in healthy machines and machines under different types of mechanical faults including static eccentricity, dynamic eccentricity, inclined rotor, and run‐out faults. Furthermore, an analytical model is developed to estimate the air‐gap permeance and the induced voltages in the healthy generator and generator under the above‐mentioned mechanical faults. Then, the performance of the generator is predicted using a two‐dimensional and three‐dimensional time stepping finite‐element method. Finally, from the stator current spectrum of the PMVG under dynamic eccentricity fault, the amplitude of the side‐band components with a specific frequency pattern is extracted and compared with experimental results. [ABSTRACT FROM AUTHOR]

Eccentricity fault is one of the prevalent faults in rotating machines which can cause other mechanical and electrical faults. This paper focuses on detecting the static and dynamic eccentricity faults in the squirrel-cage induction motors. The induction motor is modeled by the finite element method (FEM), a powerful and accurate method, using FLUX 2D software. The current signal cannot be used to detect the static and dynamic eccentricity faults especially when their severity is small. Therefore, the search-coil based method is employed and the voltage of two symmetrical search-coils is analyzed to detect and diagnose the static and dynamic faults. Since two search-coils are open-circuit, they do not affect the behavior of the induction motor. The analysis based on the principal component analysis (PCA) method shows that there exists an intelligent pattern that, firstly, is sensitive to the occurrence of eccentricity faults, even to a low degree, and secondly, has the ability to distinguish the type of fault (static or dynamic). [ABSTRACT FROM AUTHOR]

Aiming at the problems of severe vibration of switched reluctance motor (SRM) and the transfer of the peak vibration caused by newly produced radial magnetic force under static eccentricity (SE), this study proposes a vibration reduction method for SE. First, the analytical relationship between the radial magnetic force harmonics and the current harmonics is derived. 2D Fourier decomposition is used to analyse the temporal–spatial characteristics of force harmonics and the vibration response under SE. Then the expression of the force harmonic, which causes the peak vibration, is used as the optimisation function of current harmonics. According to the analyses in this study, it is difficult to consider vibration reduction and torque simultaneously by single‐order current harmonic optimisation and the unreasonable optimisation range of current will seriously affect the output performance. Therefore, a reasonable optimisation range is set based on the above conclusions and the first five order current harmonics are optimised to improve the effect of vibration suppression further. The results of the finite element simulation verify the effectiveness of this method. [ABSTRACT FROM AUTHOR]

The problem with unbalanced magnetic pull (UMP), often analyzed for induction motors, is also a huge issue in large hydro generators. This paper focuses on large vertical shaft synchronous machines describing the UMP as a function of eccentricity, irrespective of its origin on the rotor, stator, or both. The static and the dynamic eccentricity impact on the air-gap length is described through an original mathematical model in which the magnetic flux density spatial distribution is amplitude modulated and the UMP is calculated applying Maxwell's tensor. This process allows including the machine saturation when calculating the no-load rated voltage. Hence, with constant rotor excitation current, corresponding to the rated generator voltage at no-load, the magnetic field amplitude variation results in a linear function of the air-gap length variation. Seven case studies are presented comparing traditional methodology with the proposed one. Two of them are also calculated by applying the finite element method (FEM). The proposed methodology gets more realistic answers if FEM results are taken as a reference. Finally, UMP triggered by a dynamic eccentricity is shown, and the resulting force that followed the orbital eccentricity is depicted clearly. [ABSTRACT FROM AUTHOR]

Rotor eccentricity is a common fault in turbo generators, but there is currently no effective means of evaluating the eccentric state of the generators. In this article, the air‐gap permeance method was used to analyze the influence of rotor eccentricity on the no‐load main magnetic field, and the installation of U‐type detection coils within the stator core was proposed. Using this method, the dynamic eccentricity level can be measured by detecting the 2nd harmonic amplitude of the coil‐induced voltage, and the static eccentricity level can be measured using the difference in the induced voltages from the U‐type coils. Two dimensional numerical simulation results show that the U‐type detection coil is suitable for the detection of dynamic and static eccentric faults. Therefore, this method can be used for the evaluation of the eccentric state in turbo generators. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Here, analytical expressions of the unbalanced magnetic force (UMF）of the stator and the rotor under static eccentricity (SE) are deduced by using complex relative magnetic conductivity method and Maxwell stress tensor method. The frequency characteristics of the UMF are obtained. Further the influence of different eccentricity ratio on the UMF is researched. Then, an external rotor permanent magnet brushless direct current motor (PMBLDCM) with 46 poles and 51 slots used as an in‐wheel motor is taken as an example to verify the frequency characteristics by finite element analysis (FEA). The research shows that the frequency characteristics of the UMF of the stator s related to electric frequency. The frequency characteristics of the UMF of the rotor are related to the power source frequency and the rotation frequency of the wheel. It does not introduce new frequency components when the motor SE occurs. As the SE ratio increases, the amplitude of the UMF increases. The UMF without eccentricity exists in all directions with the change of the time. However, as the eccentricity ratio increases, the direction of the UMF is closer to the eccentric direction. [ABSTRACT FROM AUTHOR]

Unbalanced magnetic pull (UMP) occurred due to the uneven distribution of magnetic flux around the airgap, which can be caused by the existence of rotor eccentricity in the machines. Here, a UMP damping coefficient is introduced to explain the UMP damping effect from the counteracting flux produced by a parallel‐connected cage rotor. An empirical method is proposed to calculate the UMP using the damping coefficient and an analytical model. Using the proposed method, a four‐pole and eight‐pole squirrel cage induction machine with static eccentricity are investigated, which uses inputs from both finite element analysis and experimental work. Then, the UMP calculation for a dynamic eccentricity with the extracted parameters is done to verify the empirical method. A slip control method is described which uses a UMP/torque ratio to find the operating slip with the lowest UMP. Comparisons between results with and without slip control are made on both induction machines. It shows that great reduction in UMP can be achieved when the machine is lightly loaded. [ABSTRACT FROM AUTHOR]

This paper is focused on the design of a single protection layer to cover both the screening and damping characteristics of a large-scale high-temperature superconducting (HTS) wind turbine synchronous generator under sudden short-circuit conditions. Due to small synchronous reactance of HTS generators, short-circuit condition causes substantial fault current in the stator windings, which produces high unbalance variable magnetic field as well as substantial mechanical fluctuations issues. The former one can lead to unstable condition for HTS field windings, due to induced ac loss and field overcurrent, and the latter one can produce large fluctuations on the generator rotational speed and rotor torque angle. The proposed protection layer is designed in a way that not only screening capability is provided for the HTS windings by preventing unbalance magnetic field penetration, but desirable damping ratio is also achieved so that the fluctuations are suppressed in a proper transient time. A 10-MW-class HTS synchronous generator is modeled and simulated using finite element method under different short-circuit conditions. The temperature variation study and field overcurrent analysis are provided to show the compatibility of the proposed model. In addition, magnetic force distribution and static eccentricity fault detection analyses are provided, which guarantee the proper dynamic performance of the studied generator using the proposed protection layer. Simulation results confirm that with the proposed protection layer, both the screening and damping characteristics of the 10-MW-class HTS generator are obtained and proper transient dynamic responses are deduced for wind power applications. [ABSTRACT FROM AUTHOR]

Rotor eccentricity is a common fault in permanent magnet synchronous motors. Its effect on the vibration and noise is thoroughly investigated in this paper. The additional force harmonics due to static eccentricity and dynamic eccentricity are firstly derived with the rotational direction of force harmonics into consideration. A finite element model is built to calculate the force and two dimensional fast Fourier transform is employed to obtain the space and frequency orders under different types of eccentricity. Then, a multiphysics model is established to predict the vibration and acoustic noise under different eccentricity types and levels. Finally, the conclusions drawn from the analytical and simulation results are partly validated by experimental test. It is found that rotor eccentricity greatly intensifies the vibration and noise due to the induced force harmonics with lower space orders. Dominant vibration and noise peaks would transfer to the frequency band in the vicinity of the lower modal frequency when eccentricity occurs. [ABSTRACT FROM AUTHOR]

Different faults in permanent magnet synchronous machines (PMSMs) cause various and independent changes to the machine magnetic flux distribution, which affect the machine parameters and performance. These changes are reflected in the machine flux linkages and can be estimated from the machine voltages. In this paper, we continue the work of Haddad et al., where a method was proposed to detect and separate three types of faults in PMSMs: 1) static eccentricity; 2) demagnetization; and 3) turn-to-turn short circuit. The method proposed here is based on using the change in the commanded $d$- and $q$-axis voltages, while the machine is operating at steady state, for fault detection and separation. Simulation tests using finite element analysis (FEA) software (MAGSOFT-Flux2D) were performed under healthy and the tested fault conditions on a three-phase ten-pole fractional-slot concentrated-winding PMSM. An analytical method is proposed to estimate the commanded voltages at any operating condition, and a classification algorithm is implemented for fault detection and classification. Experimental tests were carried out and compared with FEA. The effects of the variation in the operating speed and temperature were simulated and tested to validate the detection method under different operating conditions. [ABSTRACT FROM AUTHOR]

Position sensors are inseparable part of motion control systems. Linear resolvers (LRs) are electromagnetic position sensors that are suitable for high vibration, polluted environments. The accuracy of their detected position can be affected by different mechanical faults. In this study, variety of possible mechanical faults along with their mathematical index in LRs is introduced. Static eccentricity, dynamic eccentricity, inclined mover and run out error are the presented mechanical faults that are discussed independently and simultaneously. Then, three‐dimensional non‐linear, time‐stepping finite element method is employed to investigate the performance of the studied resolver under different mechanical faults. Finally, the prototype of the studied sensor is built. An experimental test setup is designed and built in order to measure the output characteristic of the LR under studied mechanical faults. Good correlation between the experimental and simulation results is obtained. [ABSTRACT FROM AUTHOR]

An improved superposition method accounting for both permanent magnet (PM) and armature field is proposed to predict the unbalanced magnetic force (UMF) of PM machines having static/dynamic eccentricity. It virtually divides the original eccentric machine into a number of sections along the circumferential direction. Then, a series of concentric machine models are established with equivalent air‐gap lengths corresponding to those air‐gap sections. From the electromagnetic field of each concentric machine predicted by subdomain method, the air‐gap field of the original eccentric machine can be synthesised. Finally, the UMF can be easily obtained by the integral of force density along the air‐gap circumference. The effectiveness of the proposed method is validated on both rotating asymmetric and symmetrical PM machines by direct finite‐element analysis and experiment, with particular emphasis of rotor eccentricity influence on the UMF of later one. [ABSTRACT FROM AUTHOR]

Early detection and diagnosis of faults in synchronous machine (SM) are crucial since they drive critical applications. In this paper, the authors exploited the combined information from numerical simulation and experimental validation to evaluate the merits of certain fault indicators, for detecting machine faults. A specially designed SM was chosen for both simulation and measurement with the ability to physically introduce electro-mechanical failures. Shorted turn fault was made through accessible intermediate terminals of respective stator and rotor windings. Eccentricity faults of different intensity were created by suitable changeover of customized end-shield. Finite element method was used to develop healthy and faulty simulation models. The experimental setup facilitated measurement and subsequent calculation of key parameters such as stator branch currents, phase current, circulating current, rotor field current and shaft voltage. From the investigation of both simulation and experimental data, field current and shaft voltage were found to be two effective fault indicators from safety and reliability prospects. Both indicators have the ability to identify and discriminate between electro-mechanical and electrical faults. Further, it is demonstrated that with availability of physical dimensions and measured rotor parameters, a know-how can be created to detect failures, well before a catastrophic event occurs. [ABSTRACT FROM AUTHOR]

The axial flux brushless resolver without rotor windings is newly proposed resolver that has the advantages of variable reluctance (VR) resolvers for having no winding on rotor and also, its manufacturing process is much simpler than that of VR resolvers. The influence of different mechanical faults on the position error of the studied resolver is discussed. Different types of eccentricities, inclined rotor and run out error independently and simultaneously are studied using 3D time stepping finite‐element method. The results show the maximum position error is related to the resolver under static eccentricity (SE), so an optimised rotor is proposed for the studied resolver to overcome this challenge. Finally, the optimised resolver is built and the experimental tests are done to validate the simulation results. [ABSTRACT FROM AUTHOR]

In spite of numerous research activities performed so far, determination of type and exact degree of the eccentricity faults in induction motors is challenging yet. This study presents a model‐based fault diagnosis technique for identifying all the three eccentricity fault types, including static, dynamic and mixed eccentricities, with their exact degrees in the mentioned motors. This technique uses a special analytic model prepared for simulating squirrel‐cage induction motors under healthy and all eccentricity fault conditions as well as the particle swarm optimisation method. Correct performance and effectiveness of the proposed technique is verified by using simulation and experiments. Finally, an algorithm is introduced for the eccentricity fault treatment using the identified degrees of the fault components and their time trends. [ABSTRACT FROM AUTHOR]

In this article, an analytical model is developed for the magnetic field calculation of the vernier machine with a normal or an eccentric rotor. The electromagnetic performance considering the armature reaction can be taken into consideration and calculated since the magnetic vector potential is adopted. In the analytical model, the whole working domain is divided into several subdomains, and the partial differential equations of the magnetic field can be built in all subdomains. The magnetic vector potential expressions can be obtained in all subdomains through applying boundary conditions to general solutions. The perturbation method is used to describe the rotor eccentricity. The effect of static or dynamic eccentricity on the flux density, flux linkage, cogging torque, electromagnetic torque, unbalanced magnetic pull, and winding inductances is calculated and validated by the finite-element method. [ABSTRACT FROM AUTHOR]

In this research, considering slot opening and distributed winding effects, torque ripple analysis is studied for four separate synchronous reluctance machines (SynRMs) under health and eccentricity fault conditions using a mathematical method. A finite element method (FEM) validated model is produced by mathematical modeling, and numerical method is used for the machine's behavior studying with voltage source supplying. With this aim, the machine's parameters have been computed under health and eccentricity fault conditions, using modified winding function theory (MWFT). A method of dynamic and static eccentricity fault diagnosis is proposed, which uses machine vibration analysis, and the results suggest that the eccentricity fault does not have any significant effect on the machine's currents. Moreover, unbalance magnetic pull (UMP) is computed under eccentricity fault conditions and mechanical un-stability is shown. Mathematical base model and voltage source machine supply and also presenting a discrete machine modeling method are the main advantages of this paper compared with other similar works that are usually FEM-based studies or have been based on current source power supply. The research is applicable to healthy and faulty machine behavior, and the methodical modeling is obviously applicable to other machines. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents fault detection techniques in an attempt to discriminate between two common faults in axial-flux permanent magnet wind generators namely; static eccentricities and interturn short circuit faults. A combination of condition monitoring systems is proposed to achieve the discrimination; with detection techniques derived from current and vibration signatures for both faults using signal processing techniques. Parametric spectral estimation technique is applied as an alternative to the Fourier transform to process the fault signatures. This effectively overcame the problem of non-stationarity of signals due to variable wind speed as high frequency resolution was attained with less than three seconds of measurement data. The results will advance the development of standards and technical guidelines in the condition monitoring of permanent magnet synchronous generators in wind turbines. [ABSTRACT FROM AUTHOR]

This paper deals with the discernment of broken magnet and static eccentricity faults in permanent magnet synchronous motors through the stator phase current. Broken magnet and static eccentricity faults exhibit very similar fault patterns in back-electromotive force (emf) and flux spectrums. Therefore, it is essential to separate these faults from each other for a true diagnosis. In this study, stator emf and phase current waveforms are analyzed in detail to identify the discerning components and characterize their dynamic behaviors. Two-dimensional time-stepping finite-element simulations and experimental results show that the fault classification process can be implemented by using fault-dependent in-phase current fault signatures. [ABSTRACT FROM AUTHOR]

Detection of a static eccentricity fault in rotating electrical machines is possible through several measurement techniques, such as shaft voltages and flux probes. A predictive maintenance approach typically requires that the condition monitoring technique is online, accurate, and able to detect incipient faults. This paper presents a study of the optimal measurement modality that leads to a minimal identification error of the static eccentricity in synchronous machines. The Cramér–Rao lower bound technique is implemented by taking into account both measurement and model uncertainties. Numerical results are obtained using a two-dimensional finite element model and is experimentally validated on a synchronous two-pole generator. Results indicate that shaft voltage measurements are better suited to the detection of static eccentricity. [ABSTRACT FROM AUTHOR]

• Transient modal integration combined with Newmark-HHT method is proposed. • Effects of journal static eccentricity and base motion on bifurcation are discussed. • Fluid inertia effect increases oil-film reaction force for large eccentricity ratio. • Sub- and super-harmonic frequencies are stimulated under base harmonic translation. • Motions of SFD journal with static eccentricity fluctuate seriously in resonance. When an oil-lubricated rotor-bearing system is subjected to base motions, it will inevitably be affected by oil-film forces, base excitations, and inertial forces. The alignment state cannot be guaranteed over time, resulting in a static eccentricity. An inertia model for open-ended SFD incorporated three-dimensional fluid velocities and pressure distribution represented by the Reynolds number. In addition to viscous pressure, the inertial pressure distribution was also solved by finite difference method (FDM), and the oil-film forces were determined by numerical integration. Using transient modal integration method, dynamic responses of a rotor-SFD-support system considering oil-film inertia were simulated. The effects of oil-film inertia, static eccentricity, and base motions on transient responses and bifurcation behavior were discussed. The results indicate that for large eccentricity ratio, the oil-film inertia increases the reaction forces. For medium and large static eccentricity, the journal performs quasi-periodic motions. Under base harmonic translation, a series of sub- and super-harmonic frequencies k Ω ± Ω z are stimulated along with the multiples of rotational frequency k Ω and base harmonic frequency Ω z. The bifurcation motion of journal with static eccentricity fluctuates seriously in resonance. Overall, nonlinear dynamic responses of rotor-damping-support systems subjected to base motions can be evaluated during dynamics design and vibration suppression. [ABSTRACT FROM AUTHOR]

This paper describes a new method for the evaluation of the static eccentricity $$e_{s}$$ and the ratio $$\Omega _{\uptheta } $$ of uncoupled torsional to lateral frequencies in real multi-storey buildings. The above-mentioned parameters greatly affect the lateral-to-torsional coupling of the response of asymmetric systems and thus are of paramount importance in the assessment of the in-plan irregularity of buildings. The proposed method, which is a generalization of that suggested by Calderoni et al. (Earthq Spectra 18(2):219-231, ), allows the calculation of the static eccentricity $$e_{s}$$ and the ratio $$\Omega _{\uptheta } $$ from the structural response to arbitrary distributions of forces and torsional couples. The effectiveness of the method is validated on some regularly and non-regularly asymmetric buildings characterised by different in-plan irregularity. The analyses demonstrate that the results of the method are rigorous in the case of regularly asymmetric systems and only slightly depend upon the heightwise distribution of the forces in the case of non-regularly asymmetric systems. Finally, the values of the static eccentricity $$e_{s}$$ and the ratio $$\Omega _{\uptheta } $$ resulting from the proposed method are compared to those obtained by means of the procedure suggested by Makarios and Anastassiadis in (Struct Des Tall Spec Build 7(1):33-55, ; Struct Des Tall Spec Build 7(1):57-71, ) . [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The paper shows a theoretical rotor dynamic analysis of two-pole induction motors regarding excitation due to static rotor eccentricity, which causes an oscillating magnetic force in the air gap of the machine. The hereby caused rotor vibrations are mathematically described, showing the orbit movements of the rotor centre, the shaft journals and the bearing housings. The influence of the rotor speed as well as influence of the direction of the magnetic force on the vibration behavior is investigated, based on a numerical example. On the one hand the aim of the paper is to derive the mathematical coherences-based on a simplified rotor dynamic model-between rotor dynamics, electromagnetic and the oil film characteristics of the sleeve bearings for two-pole induction machines, considering electromagnetic excitation due to a static rotor eccentricity. On the other hand the aim is to derive a method for calculating the maximum height of the shaft vibrations-as a worst case-caused by a static rotor eccentricity. Therefore the paper shall prepare the basis for implementing this method into more detailed numerical programs, e.g., finite element programs. [ABSTRACT FROM AUTHOR]

This paper studies on the fault analysis of 3-phase cage induction motor with the mixed fault of the static eccentricity and the broken rotor bars at steady state. A mathematical fault model is presented by the coupled magnetic circuit approach. The calculation of winding inductances is derived by means of a winding function theory. The stator current and the torque are obtained by means of the coupled magnetic circuit method and Park's transformation. The characteristics of single fault and mixed fault are analyzed. From the simulation results it is shown that there is its own peculiar frequency component obtained by the spectrum analysis of the stator current in the case of a single fault. But in the case of mixed fault, there is a mutual effect between two faults. From the comparison with FEM results, it is shown that the proposed approach can be simulated to diagnose faults in 3-phase cage induction motor. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This article models the simultaneous presence of broken rotor bars and static eccentricity (mixed fault) faults in a three-phase squirrel-cage induction motor using the time-stepping finite element method. A stator current signal is then used for the noninvasive diagnosis of mixed fault. The major problem in the analysis of an induction motor under mixed fault is the determination of the number of broken rotor bars and static eccentricity degree. Broken bars cause an asymmetrical rotor cage and influence the amplitude of the harmonic components. On the other hand, these harmonics are normally used to diagnose the static eccentricity degree independently. Also, static eccentricity leads to asymmetrical air gap flux and flux density distribution, which influence the amplitude of the harmonic components. Therefore, it is not easy to discriminate the contribution of each fault in the mixed-fault motor. Spectrum analysis of the stator current around the main component is used to diagnose the mixed fault and to determine the number of broken rotor bars. It is shown that this spectrum cannot be used to precisely detect the static eccentricity. Therefore, the spectrum analysis of current around the principle slot harmonic is used to diagnose the static eccentricity degree in the mixed-fault case. [ABSTRACT FROM AUTHOR]

Static eccentricity (SE) is frequently generated by manufacturing processes. As the nonuniformity of the air-gap length is caused by the SE, the torque ripple and cogging torque increase in the motor. This study analyzes the distorted back electromotive force (EMF) and cogging torque due to SE. Further, a motor design considering SE is performed for stable back EMF and low cogging torque. First, the SE was diagnosed and analyzed using the back EMF and cogging torque measured from the test results of the base model. In addition, the rotor position was calculated using the unbalanced back EMF due to the SE. The calculated rotor position is used when analyzing phenomena due to SE and applied to robust design. Subsequently, robust design optimization was performed to improve the unbalanced back EMF and cogging torque due to SE. Using finite element analysis (FEA) considering SE, the shape of the stator was designed based on the base model. The estimated rotor position from the base model was applied to the optimum model to confirm its robustness from SE's effects. Finally, the base and optimum models were compared through the test results. [ABSTRACT FROM AUTHOR]

This article investigates the combined partial demagnetization and static eccentricity fault in an Axial Flux Permanent Magnet (AFPM) Synchronous Generator. The machine is simulated using 3D FEM, while the EMF spectrum is analyzed in order to export the fault related harmonics using the FFT analysis. Firstly, the partial demagnetization fault, without the coexistence of eccentricity, and both the static angular and axis eccentricity faults, without the coexistence of partial demagnetization, are studied. In the case of eccentricity fault, the phase EMF sum spectrum has also been used as a diagnostic mean, because, when only eccentricity fault exists in the generator (either angular or axis) new harmonics do not appear in the EMF spectrum. Secondly the combination of partial demagnetization fault with static axis and static angular eccentricity is investigated and different comparisons are made when the demagnetization and the eccentricity level changes. The investigation revealed that the combination of eccentricity and demagnetization creates new harmonics in the EMF spectrum. The novelty of the article is that these combined faults are studied for the first time in the international literature, and the phase EMF sum spectrum has not been previously used for eccentricity diagnosis in this machine type. [ABSTRACT FROM AUTHOR]

Annular seals of turbomachinery usually suffer from various degrees of eccentricities and disturbances due to the rotor–stator misalignment and radial loads, while the discussion of annular seal under both large static eccentricities and dynamic disturbances is relatively limited. In this paper, the applicability of linear assumption and reliability of nonlinear dynamic model for eccentric annular seals under large eccentricities and disturbances is discussed based on the investigation of seals with various rotor motions through computational fluid dynamics (CFD). After the validation of transient CFD methods by comparison with experimental and bulk theory results, the dynamic behaviors of annular seal are analyzed by adopting both direct transient simulations and the nonlinear Muszynska model. The results show that the nonlinear dynamic model based on rotor circular whirls around seal center can predict the fluid excitations of different types of rotor motions well under small static eccentricities, while it is limited severely with large static eccentricities, which indicates that the dynamic characteristics of annular seal under large eccentricities are related with the rotor's motion ways. The paper provides a reference for studies of rotor–seal system with complex rotor motions considering radial loads or running across the resonance region. [ABSTRACT FROM AUTHOR]

The paper firstly summarizes a simple analytical model of the air gap flux-density distribution for isotropic permanent magnet (PM) synchronous machines, in the presence of static eccentricity. The model was proposed by the authors in a previous paper and is based on an efficacious analytical expression of the variable length of air gap magnetic field lines which occur in eccentric brushless machines with surface-mounted permanent magnets. The approximate expression of the air gap field makes it possible to achieve a mathematical model with concentrated parameters close to that of a PM machine without eccentricity. The expression of the armature voltages and electromagnetic torque are found, also with reference to steady-state operating conditions at fixed rotor speed and impressed currents. The differences introduced by the considered type of eccentricity are evaluated and highlighted especially with reference to the air gap inductance and to waveforms and frequency spectra of voltages and shaft torque. Numerical results in a case-study of an 8-pole, 110 kW PM motor are compared to those obtained by using finite element analysis. [ABSTRACT FROM AUTHOR]

Large synchronous generators are the heart of the modern world, while producing the vast majority of the electric power consumed globally. Although they are robust devices, they are prone to degradation and failure. If such failures are not detected at an early stage, then the negative impact may be catastrophic in terms of financial costs, repair times, human lives and quality of life. This is the reason for continuous research in the field of condition monitoring aiming towards the reliable operation of synchronous generators. This paper proposes a novel technique for the diagnosis of the static eccentricity in synchronous generators. The proposed approach is off-line and non-intrusive, allowing the estimation of the fault severity with stator current measurements only. The performed work has been carried out with Finite Element Simulations and extensive experimental testing. [ABSTRACT FROM AUTHOR]