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Magnetic flux leakage from the rotor core bridge must be improved in interior permanent magnet motors to improve their performance. The partial non-magnetization of bridges is effective in reducing magnetic flux leakage. In our previous studies, we proposed a new partial nonmagnetization process for silicon steel, which was used for the rotor core. The portion of the silicon steel sheets that becomes a bridge after pressing can be non-magnetized by melting and mixing Ni-Cr-B alloy powder with the silicon steel sheets using a laser beam and then laminated to produce the rotor core. In this study, the effect of B addition to Ni-Cr alloy powder was widely investigated to optimize the B addition amount. Based on the appearance, solidification defect, and magnetic and mechanical strength properties of the improved portion, the optimal content of B was within the range of 0.5-1.0 mass%. Furthermore, core sheet samples with an improved portion, which had the improved length of 1.0mm and has the composition of Fe-13.9 mass%Cr-15.1 mass%Ni-2.3 mass%Si-0.5 mass%B, were prepared by laser and press processing. A rotor core was fabricated using core sheets and evaluated for its magnetic flux and high-speed rotation for practical use. The prototype rotor core exhibited a 32% higher magnetic force and could rotate at speeds of up to 43,000 rotations. It is expected that the size of interior permanent magnet motors will be reduced due to the increased magnetic force. [ABSTRACT FROM AUTHOR]

The interturn short circuit fault is one of the common faults in power transformers. At present, research on interturn short circuit faults focuses on high, medium, and low voltage windings, while there is relatively little research on interturn short circuit in regulating windings. Specifically, there is a lack of reported studies on the transient electromagnetic processes, magnetic field distribution, and electromagnetic force characteristics of interturn short circuits in regulating windings unconnected to the circuit. This study presents an actual fault scenario involving interturn short circuits occurring in the untapped portion of the regulating windings of a specific power transformer. A field-circuit coupled model was established to analyze the transient electromagnetic processes during the fault, and the model's effectiveness was validated by comparing its results with actual fault recording data. Additionally, the magnetic field distribution and electromagnetic force characteristics during the fault were analyzed, and discussions were carried out regarding various ratios of short-circuit turns in the regulating windings. The results indicate that even when an interturn short circuit occurs in the portion of the regulating winding that is not connected to the circuit, the current in the short-circuited turns can reach several tens of times the rated value. Additionally, the leakage magnetic field and the electromagnetic force experienced by the short-circuited ring also increase significantly. The short-circuit ratio has a significant impact on the current of the short-circuited ring, leakage magnetic field intensity, and electromagnetic force. This study contributes to a better understanding of the impact of interturn shortcircuit faults in the untapped portion of the regulating windings, offering crucial technical support for fault diagnosis and prevention of power transformers. [ABSTRACT FROM AUTHOR]

Internal permanent magnet motors suffer from leakage flux in their rotor core bridges, which can be removed through the partial nonmagnetization of the bridges. In a previous study, a process was proposed in which the bridged portion of the silicon steel sheet was non-magnetized after pressing by melting, an Ni--Cr alloy powder was added to the silicon steel sheet using a laser, and the rotor core was produced via lamination. However, because the final solidification step produced solidification defects, such as cracks and shrinkage cavities, a homogenous alternative step that does not produce solidification defects needs to be developed. To reduce the area of improvement, we previously investigated a chemical composition that suppressed solidification defect formation. The addition of B to the improved portion suppressed the formation of cracks and shrinkage cavities, and a crack-suppression mechanism was proposed. In this study, we focus on the mechanism of shrinkage cavity suppression. We determine that the solidification shrinkage rate decreases owing to the precipitation of Cr2B, which has a lower density than the austenite phase, and results in the suppression of the shrinkage cavities. Minimization of the area of nonmagnetic improvement is possible by suppressing solidification defects. Consequently, the laser processing speed per piece and amount of expensive nickel are reduced. These new alloys show promise for practical partial non-magnetizing applications. [ABSTRACT FROM AUTHOR]

This paper introduces an evaluation of the flux air gaps of Shunt Reactors (SRs) to effectively mitigate fringing and leakage fluxes along the height of the iron core. The assessment of these discretely distributed flux air gaps in SRs is a rigorous and challenging process. To define their exact number, the case of one flux air gap is analyzed and investigated to observe/simulate the influence of the flux density distribution and the leakage flux along the air gaps on the reactive power and the operation conditions of the SR. Based on that, to reduce leakage flux, a large flux air gap is divided into smaller ones. Initially, an analytic model is presented to define the main parameters of the SRs. Then, a finite element method is developed to simulate electromagnetic quantities, such as the magnetic flux density, leakage flux, and electromagnetic force. The obtained results can help manufacturers define the exact number of flux air gaps along the iron core of the SR. From that, a suitable technology can be given in manufacturing high voltage SRs applied to high or super high voltage transmission lines. [ABSTRACT FROM AUTHOR]

The interturn short circuit fault is one of the common faults in power transformers. At present, research on interturn short circuit faults focuses on high, medium, and low voltage windings, while there is relatively little research on interturn short circuit in regulating windings. Specifically, there is a lack of reported studies on the transient electromagnetic processes, magnetic field distribution, and electromagnetic force characteristics of interturn short circuits in regulating windings unconnected to the circuit. This study presents an actual fault scenario involving interturn short circuits occurring in the untapped portion of the regulating windings of a specific power transformer. A field-circuit coupled model was established to analyze the transient electromagnetic processes during the fault, and the model’s effectiveness was validated by comparing its results with actual fault recording data. Additionally, the magnetic field distribution and electromagnetic force characteristics during the fault were analyzed, and discussions were carried out regarding various ratios of short-circuit turns in the regulating windings. The results indicate that even when an interturn short circuit occurs in the portion of the regulating winding that is not connected to the circuit, the current in the short-circuited turns can reach several tens of times the rated value. Additionally, the leakage magnetic field and the electromagnetic force experienced by the short-circuited ring also increase significantly. The short-circuit ratio has a significant impact on the current of the short-circuited ring, leakage magnetic field intensity, and electromagnetic force. This study contributes to a better understanding of the impact of interturn short-circuit faults in the untapped portion of the regulating windings, offering crucial technical support for fault diagnosis and prevention of power transformers.

The aim of this study is to examine and analyze the axial and radial forces, electromagnetic forces (EMFs) acting on the low and high-voltage windings of an amorphous core transformer via the two different approaches: an analytic approach and a 3-D finite element method (FEM). Firstly, the analytic method is proposed to analyze the distribution of leakage magnetic field in the magnetic circuit and the forces acting on the transformer windings. The FEM embedded in the Ansys Maxwell tool is then proposed to compute and simulate the axial and radial forces under three different operating conditions: no-load, rated full-load, and short-circuit. The obtained results from two different methods such as the rated voltage, rated current, short-circuit current, axial and radial forces and EMFs in the low and highvoltage windings are finally compared to illustrate an agreement of methods. The validation of the methods is applied on a three-phase amorphous core transformer of 1600kVA-22/0.4kV. [ABSTRACT FROM AUTHOR]

Leakage flux magnitude and pattern greatly affect transformer short-circuit resistance. In this paper, finite element calculations and experimental measurements is used to calculate the leakage magnetic field of a transformer. This paper analyzed the radial and axial leakage flux distribution of each winding under different operating conditions to obtain a comprehensive view of the magnetic flux leakage distribution in all directions. This analysis can provide valuable insights for optimizing the anti-short-circuit ability of transformers.

Electromagnetic forces generated by the short circuit current and leakage flux in low- and high-voltage windings of distribution transformers as well as amorphous core transformers will cause the translation, destruction, and explosion of the windings. Thus, the investigation of these forces plays a significant role for researchers and manufacturers. Many authors have recently used the finite element method to analyze electromagnetic forces. In this paper, an analytic model is first developed for magnetic vector potential formulations to compute the electromagnetic forces (i.e., axial and radial forces) acting on the low- and high-voltage windings of an amorphous core transformer. The finite element technique is then presented to validate the results obtained from the analytical model. The developed model is applied to an actual problem.

Leakage flux in rotor core bridges is a problem specific to interior permanent-magnet (IPM) motors. It is widely known that the partial non-magnetization of bridges reduces the magnetic flux leakage. In a previous study, a process was proposed whereby a part of the silicon steel sheet that bridges after pressing was non-magnetized by melting and mixing Ni--Cr alloy powder with a silicon steel sheet using a laser, and the rotor core was produced by laminating them. However, because the final solidification part had solidification defects, such as cracks and shrinkage cavity, the process was proposed to leave a homogenous part free of solidification defects. Therefore, the area of the improved portion increased. We focused on developing a new alloy for non-magnetic improvement to suppress solidification defects. The improved portion was melted and mixed using a laser with various B contents to obtain a composition of Fe--(15--20) mass%Ni--(15--20) mass%Cr--(2--3) mass%Si--(0--1.6) mass%B. Large cracks and large shrinkage cavity were observed in the boron-free alloy. The cracks and shrinkage cavity decreased with an increase in the B content. The minimization of the area of non-magnetic improvement is possible by suppressing solidification defects. Consequently, the laser processing speed per piece and the amount of expensive nickel were reduced. These new alloys show promise for practical applications in the partial non-magnetization process. [ABSTRACT FROM AUTHOR]

Flux leakage in the rotor core bridges is a problem specific to interior permanent magnet motors and has been unsolved till date. It is widely known that if the bridges are partially non-magnetically improved with low magnetic polarization, the leakage flux will be smaller, and the rotor will have a higher magnetic flux. We proposed that the portion of the silicon steel sheets that becomes the bridge after pressing can be nonmagnetized and laminated to fabricate the rotor core. Partially non-magnetic material with a polarization of almost zero was obtained by melting and mixing NiCr alloy powder with the silicon steel sheets. This non-magnetic improvement treatment was applied to the bridge in the rotor core sheet, in which the non-magnetic area width was 1.45 mm, and the prototype rotor core was fabricated by laminating 60 rotor core sheets. Upon measurement, the rotor core showed approximately 35% higher magnetic flux than a conventional one, with the actual value nearly identical to that obtained from the magnetic field analysis. [ABSTRACT FROM AUTHOR]

Wound-rotor resolvers are the oldest and most widely used resolvers. They are two-phase synchronous generators with high-frequency AC excitation. Rotary Transformers (RTs) are used to supply the rotating excitation winding of the resolver. Although RTs offer the benefits of contactless power transmission, the harmonic contents of the secondary voltage, phase shift error between the primary and secondary voltages, and high leakage flux are the main challenges in their applications in the resolvers. The current study aims to examine different configurations of the ferromagnetic core of the RTs to overcome the mentioned problems. To this end, all simulations were done using 3D Time Variant Finite Element Method (TVFEM), and the best configuration was chosen for experimental prototyping and measurements. Close agreement between the simulation and experimental test results approved the performed analysis. [ABSTRACT FROM AUTHOR]

This paper has developed electromagnetic equations based an analytical model to design a three-phase line start permanent magnet synchronous motor (LSPMSM) of 2.2 kW. In order to enhance the torque and efficiency of this machine, an optimized slot shape of rotor permanent magnet is proposed. The analytical model is first presented to evaluate the magnetic characteristics, and then analytical expressions are derived under the open circuit condition. The influence of the magnet size variables on the analytical model is considered to investigate the magnetic leakage flux and flux density distribution in air gaps. Moreover, the variation of design has a significant impact on the steady-state performance characteristics of this motor. In addition, in order to check the output results from the analytical model, a finite element method is developed to evaluate these solutions. Finally, experimental and simulation results have been compared and analyzed to validate the development of method. [ABSTRACT FROM AUTHOR]

Abstract This paper addresses the influence of the primary and secondary resistances on the behavior of minor hysteresis loops when the electromagnetic device is fed by three-level PWM (pulse width modulation) voltage. To study the device transferring energy to a load, the experimental approaches are different of traditional procedures to material characterization, where problems inherent to the process are added. Analytical, FEM and experimental analysis are performed on a toroidal transformer equipped with a flux sensing coil. The leakage fluxes related to the primary and secondary currents are shown to cause errors in the measurement of the core magnetization current. A solution to mitigate this problem is employed, consisting in twisting and winding together primary and secondary conductors. Experimental methodologies for obtaining the value of the iron losses when the device is transferring energy to a load are also performed. The study shown showed that supply voltage with three-level PWM waveform causes minor hysteresis loops and the greater the resistance value of the excitation winding, the larger the areas of the minor hysteresis loops. On the other hand, by increasing the energy transferring to a load the minor loops areas tend to decrease.

In the current research of the magnetic circuit model of the servo valve torque motor, the magnetic flux leaking from working air-gaps is regarded as constant. However, the working air-gaps leakage flux varies with the armature rotation angle, which affects the accuracy of the existing mathematical model of the torque motor. To solve this problem, a new mathematical model of the torque motor with two working air-gaps is built. First, different from the previous model, the variation of the working air-gaps leakage flux is considered in the magnetic circuit model. A more detailed mathematical model of the torque motor is established based on the magnetic circuit model. Second, the finite element method is used to reveal that there is a linear relationship between working air-gaps leakage flux and armature rotation angle in a certain range of rotation angles. Then, the new model is validated by numerical calculation, which indicates that the theoretical results calculated by this new model show better agreement with the simulation results compared to the previous model when the armature rotation angle increases. Further, the theoretical results of the electromagnetic torque constant and magnetic spring stiffness acquired by the new model and the previous model are compared. The comparison shows that the variation of the working air-gaps leakage flux has the greatest influence on the magnetic spring stiffness. Finally, the experiments on the torque motor are conducted to verify the accuracy of the new model. The theoretical results obtained by this new model are better consistent with the experimental results than that obtained by the previous model. This study shows that considering the variation of working air-gaps leakage flux is valuable to improve the accuracy of the magnetic circuit model of the torque motor, which provides an effective guidance for the structural optimization and performance prediction of the torque motor. [ABSTRACT FROM AUTHOR]

With the aid of mathematical and physical simulation the electromagnetic field distributions in the end zone of a powerful turbogenerator has been obtained. On the basis of the comparison of the axial component of the magnetic induction on the surface of the extreme package of the stator core of the large-scale physical and mathematical models with the data of the field experiment, conclusions are drawn about the reliability of the results obtained. The data of the simulation and the field experiment correspond to the same turbogenerator, which makes it possible to evaluate the correctness of the construction of the mathematical model. It is shown that physical modeling makes it possible to evaluate the regularities of the distribution of the electromagnetic field (without obtaining accurate quantitative indicators) and can be used for qualitative comparison of the effectiveness of various design solutions of the end zone of the stator. However, such models have not become widely used, since numerous studies are required to form meaningful and sufficiently detailed conclusions about the parameters and characteristics of the object, the design of the end zone of high-power generators is complex, and the calculation of three-dimensional models is time-consuming and even with modern computer technology is associated with a number of simplifying factors. In mathematical modeling, a sequential logical transition is applied from a simple model of the central part of the machine to a more complex model of the end zone using preliminary results, which makes it possible to obtain data on the distribution of the electromagnetic field in complex areas. With the help of specialized software, a model has been created that is quite flexible in terms of modifying individual components, characterized by accessibility, visibility and unlimited possibilities for experimentation, including predicting situations that have not previously occurred or can give unpredictable results.

This article investigates the effect of airgap length on the electromagnetic performance of direct-drive surface mounted permanent magnet Vernier (SPM-V) machines with different power ratings. Using 3 kW machine as an example, its performance is comprehensively compared with a conventional SPM machine with the same airgap lengths using two-dimensional finite-element analysis. For each airgap length, the slot/pole number combination for the SPM-V machine is investigated to achieve the optimal performance compared to the conventional SPM machine. In order to make the study more generic, the slot/pole number and the airgap length variations are expressed as normalized pole pitch, i.e., $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ (ratio of rotor pole pitch to electromagnetic airgap length). The results show that for 3 kW machines, $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ >2.2 is a good design criterion for the SPM-V machines to achieve higher average torque and efficiency than the conventional SPM machines. In addition, a reasonably good power factor (>0.9 in this case) can be achieved. Although the power factor of SPM-V machines drops significantly at multi-MW power level, i.e., 3 and 10 MW, the criterion $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ >2.2 still results in achieving a performance closest to their optimal capability. However, when $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ >2.2, special consideration should be paid to avoid potential irreversible magnet demagnetization at multi-MW power levels. [ABSTRACT FROM AUTHOR]

This paper presents a modelling approach for a transformer with different saturation levels. First, the magnetic field distributions at different saturation levels in the transformer are analyzed by using numerical simulations. Then, the characteristics of the leakage magnetic flux are analyzed, and the magnetic circuits with varying leakage reluctance topologies are modeled. Finally, based on the mature duality relationship between electric and magnetic circuits, the equivalent electric circuit models are obtained. These kinds of models embody the effect of different saturation levels on the connection points of the leakage flux branches, and it can fully reflect the various working states of the transformer. The accuracy of the models is verified by comparing the circuit simulation results with those of FEM transient simulations. [ABSTRACT FROM AUTHOR]

This paper addresses the influence of the primary and secondary resistances on the behavior of minor hysteresis loops when the electromagnetic device is fed by three-level PWM (pulse width modulation) voltage. To study the device transferring energy to a load, the experimental approaches are different of traditional procedures to material characterization, where problems inherent to the process are added. Analytical, FEM and experimental analysis are performed on a toroidal transformer equipped with a flux sensing coil. The leakage fluxes related to the primary and secondary currents are shown to cause errors in the measurement of the core magnetization current. A solution to mitigate this problem is employed, consisting in twisting and winding together primary and secondary conductors. Experimental methodologies for obtaining the value of the iron losses when the device is transferring energy to a load are also performed. The study showed that supply voltage with three-level PWM waveform causes minor hysteresis loops and the greater the resistance value of the excitation winding, the larger the areas of the minor hysteresis loops. On the other hand, by increasing the energy transferring to a load the minor loops areas tend to decrease. [ABSTRACT FROM AUTHOR]

A quasi-three-dimensional field mathematical model of the electromagnetic field and heat transfer processes in end zone of a powerful turbogenerator has been developed. A model is the intermediate version between two-dimensional and three-dimensional solutions and is based on the numeral calculations in transversal and longitudinal sections of turbogenerator, interconnected by a complex of boundary conditions. On the first stage, a two-dimensional field model of the electromagnetic field in transversal section of central zone of a turbogenerator is considered. Then, taking into account the field distribution in central part, the magnetic field in longitudinal section is simulated. In response to the symmetry of the machine along axial and radial directions, the calculation area of end zone is considered as a half of the rotor section along its axis and the section of the stator core tooth in the tangential direction (circumferentially). Having taken the distribution of electromagnetic parameters obtained in the load mode of the machine as the initial data, the thermal losses in the elements and nodes of the end zone are determined. As a result of solving the joint problem of calculating the electromagnetic field and heat exchange processes, the distribution of heating has been obtained not only on the surface, but also inside the structural parts of the end zone. In particular, it has been found that the maximum temperature of 97.3 °C takes place in the tooth area of the end package of the stator core. This is explained by the combined effect of the main radial field, the axial leakage flux of the frontal portions of the stator and rotor windings, as well as by the “buckling” of a portion of the main flux out of the air gap. In addition, the pressure plate shielding effect is the cause of local field concentration in the toothed zone of the end package. The presented model makes it possible as early as at the design stage to evaluate the efficiency of design solutions for the formation of the end zone of the turbogenerator stator for different load modes of the machine, including the modes of consumption of reactive power.

Motor current signature analysis (MCSA) has been accepted in the field as a reliable means of detecting faults in the rotor cage of induction motors. However, there are many limitations to MCSA-based detection for other types of faults including rotor eccentricity and load defects. Recently, there has been increasing interest in airgap or leakage flux monitoring as an alternative to replace or complement MCSA. Flux monitoring can provide a reliable means of detecting rotor faults since anomalies in the rotor magnetomotive force or airgap can be directly observed. In this article, a new method based on monitoring the attenuation of rotor rotational frequency sidebands in the flux spectra is proposed for reliable detection and classification of rotor cage and eccentricity faults. It is also shown that flux monitoring can provide detection of rotor faults that is insensitive to the load defects. An experimental study under controlled broken bar, eccentricity, misalignment, and load unbalance conditions are given to support the claims. The results show that rotor cage, eccentricity, and load defects can be detected and distinguished for cases where MCSA alone is ineffective. A comparative evaluation between the proposed flux monitoring method and existing methods (MCSA, vibration analysis) is also given. [ABSTRACT FROM AUTHOR]

With the increasing demand for high power density and high-speed electrical machines, ac copper loss issue becomes more severe and poses a significant challenge for machine design. This article proposes a suppression technique by transposing the coil connection in the same branch to balance the inductances of parallel strands, thus reducing the circulating current ac loss. Compared to the commonly used transposition method implemented within one coil (e.g., Litz wire), the proposed method can be beneficial to reduce the transposition points and have no influence on the slot filling factor. The proposed idea is investigated by the field-circuit coupled finite element analysis (FEA), taking the bundle-level circulating current into account. It shows that the copper loss can be reduced by 17% compared to the nontransposed one at 400 Hz for a studied 12-slot 10-pole permanent magnet machine. The influence of winding layout and slot/pole combination on the effectiveness of the proposed transposition method is also investigated. Finally, experiments are implemented on a designed test-rig to validate the FEA method and the effectiveness of the new transposition. [ABSTRACT FROM AUTHOR]

To execute soft switching methods in resonant power converters, transformers with larger leakage inductance are getting more attention. Many papers have constructed various concepts in this regard. However, a discussion about, how the transformer efficiency is affected is lacking in the literature. This paper analyses the effects of the increased leakage inductance on the performance of the transformer. A transformer for increased leakage inductance is modelled and constructed to investigate the losses. The model discusses the effects of increased leakage inductance either by increasing the inter-winding spacing or by integrating the magnetic shunt within the transformer. The investigations show that increasing the leakage inductance by inserting a magnetic shunt can have severe degrading effects on the performance of the transformer, if not designed adequately. Additional losses are also calculated and the effects are verified by the experiments. [ABSTRACT FROM AUTHOR]

This article presents a quasi-3-D analytical model for double-sided axial-flux permanent magnet machines (AFPMMs) with coreless structures. A simple, fast, and accurate technique is developed to calculate flux densities in different parts of the AFPMM combining the solution of Maxwell’s equations and the magnetic equivalent circuit (MEC). In this technique, Maxwell’s equations are used to generate flux sources that are used in the reluctance network of the MEC. After calculating all the reluctances and flux sources, the magnetic flux densities are obtained. This method takes into account the effects of permanent magnet (PM) reluctance, leakage flux between PM-to-PM, PM-to-rotor leakage flux at different PM edges, and the fringing flux effect. By considering these leakage fluxes as a factor called variation function in the design procedure of the machine, the analysis time is dramatically reduced compared to numerical methods while maintained high reliability. It should be noted that since considering saturation phenomenon effects in coreless AFPMM analysis does not give rise to significantly different performances, they are not included in the proposed model. Furthermore, the machine’s main features, such as the axial and tangential components of the no-load flux density in the air-gap and stator areas, as well as the back electromotive force (EMF), are derived by using magnetic field solutions and simple equivalent circuits. Finally, to validate the accuracy of the proposed method, the analytical results are compared to the case that no leakage fluxes are included in the analytical model and to the 3-D finite-element analysis (FEA) in terms of computation time and accuracy. [ABSTRACT FROM AUTHOR]

In this article, to improve the adjustment ability of air gap flux, a new interior permanent magnet (IPM) synchronous machine with permeability modulation characteristics is proposed for electric vehicles’ (EVs) potential applications. The main trait of the machine structure is that a bridge between the rotor poles is intentionally established, which can produce a smooth magnetic path for the leakage flux. Thus, the flux leakage state can be adjusted by controlling the magnetic saturation of the bridge according to the machine load current. To clarify this feature, the machine performances are investigated by theoretical analysis and finite-element method. Finally, the designed machine is manufactured and its performances are verified by experiments. Both the simulation and experimental results prove that the torque of the proposed machine under loaded conditions can be flexibly adjusted by the magnetic permeability modulation without any complex control strategy. [ABSTRACT FROM AUTHOR]

In the conventional flux reversal permanent magnet (FRPM) machine, half of the permanent magnets (PMs) produce the leakage flux at each operation moment, which results in poor utilization of magnets. In order to improve the magnetic flux utilization in the FRPM machine, this article proposes a novel consequent-pole FRPM machine topology with Halbach array magnets in the top of rotor slot, where Halbach array magnets in the rotor slot are employed to guide the flux into the rotor teeth to reduce the leakage flux. Therefore, compared with the conventional FRPM machine, the proposed counterpart exhibits larger back-electromotive force (back EMF) and torque density. In this article, the structure and operation principle of the proposed FRPM machine are investigated based on a classical 12-slot/17-pole FRPM machine topology. Furthermore, the electromagnetic performances of the proposed machine, including back EMF, electromagnetic torque, losses, flux-weakening, and overload capabilities are obtained and compared with the conventional machine by the finite-element method (FEM). [ABSTRACT FROM AUTHOR]

The thin wobble motors that are required to hold rating shafts employ an electropermanent magnet. This turns the holding force on and off by applying a momentary electrical pulse. To design the magnet devices without the need for finite element analyses, a theoretical force model is necessary for predicting the attractive force. In this paper, first, a force model is derived by estimating the permeance around the air gap. A magnetic circuit is constructed, employing a relatively simple method to build the model in clouding leakage flux. Thus, the basic structure and driving principle are also presented. Next, an analytical force model is constructed on the basis of distribution parameter analysis between the stator and the rotating shaft. The design of the electromagnet core and the control method are presented. Finally, a prototype model of the motor that is 30 mm in diameter and 7 mm in thick is fabricated. The two models are verified by comparing the results of FEM with the results of the experiments. They can properly predict the attractive force, so the thin wobble motor with holding force can be applied in portable electric equipment. [ABSTRACT FROM AUTHOR]

This paper presents a novel leakage model for transformers that includes losses. This new model is physically based (topological) and it is possible to connect it to a topological core model without using any fictitious windings. The methods to calculate its parameters from standard test data and from design data are detailed within the paper. The results show that the new coupled leakage model with losses is able to match exactly the test report, when using standard test data. Preliminary investigations show that the results are very close to measurements, when using design data. [ABSTRACT FROM AUTHOR]

The appealing advantages of high-temperature superconducting (HTS) power transformers over conventional ones have attracted transformer manufacturing companies, power companies, research institutes, and universities worldwide to conduct research and development in this field. Unfortunately, HTS transformers are more vulnerable to mechanical stresses than conventional transformers. The results of the interaction between current carrying windings and leakage magnetic fluxes are the electromagnetic forces, which act on transformer windings. Under short circuit events, these forces are remarkable, and, therefore, catastrophic failure of transformer may arise. Flux-diverter applications have been reported in earlier literatures for increasing critical current or decreasing ac losses in HTS transformers. In this paper, a genetic algorithm based method is employed for the optimal design of flux diverter to minimize the axial short circuit force, in design stage of a sample 132/13.8 kV, 50 MVA three-phase core type HTS transformer. In this paper, the optimal dimensions, placement, and permeability of a flux diverter have been determined. It has been shown that utilizing this optimized flux diverter, the axial short circuit forces have been reduced significantly. Electromagnetic modeling and simulations, by the application of finite element method, have been employed for the verification of the analytical method results. A high degree of consistency has been observed between the analytical results and the simulation results. [ABSTRACT FROM AUTHOR]

Magnetic field distribution in the airgap of rotating machines, consisting of tangential and normal components, determines the instantaneous value of torque. Lorentz force (LF), Maxwell stress tensor (MST), and virtual work (VW) methods are commonly used to estimate its value. In their well-known forms, as used by design engineers of rotating machines, these three methods reflect distinct significance for field components. The LF method does not require the distribution of tangential field components to compute torque, whereas in MST and VW, it is required. In this article, torque expression-based equivalence of LF, MST, and VW methods is presented, starting from a simple two-coil conceptual system. Using this equivalence as a basis, certain indicative factors are derived, which provide insights on the typical significance of the tangential component in average and ripple torque. The analysis presented here helps designers obtain a better overview of the method-specific significance of field components and flux paths in instantaneous torque, from a numerical perspective. [ABSTRACT FROM AUTHOR]

• This study examines surface-mounted permanent magnet synchronous motors' eccentricity faults. • An analytical modeling, finite element simulation, and experimental study were carried out for this research. • This study suggests a flux base method for eccentricity fault detection based on moving the flux-measuring sensor around the motor and mapping the stray flux outside it. • The proposed method is easy, effective, and more convenient for field testing and enhances the index of the performance per cost in online monitoring. • The methodology can be used for any motor configuration and operating conditions. The paper discusses the impact of rotor eccentricity in permanent magnet synchronous motors (PMSMs), which leads to increased motor vibration and unbalanced magnetic pull, resulting in accelerated aging of motor parts. Undetected eccentricity in the motor can exacerbate these issues and lead to a higher risk of stator-rotor contact and forced outages. The study proposes a technique for detecting eccentricity faults using an analog magnetic field sensor outside the motor, without requiring the sensor to be installed within the motor. The proposed technique was evaluated using analytical calculations, 2-D finite elements, and experimental results. The proposed method was evaluated in different scenarios and it was found to be capable of providing detection and identification of parallel and inclined eccentricity. The size of the magnetic field at a specific point in the outer space of the motor was estimated to be 26 μ T , 30 μ T , and 43 μ T , respectively, through analytical modeling in healthy conditions, 10% and 30% eccentricity, and it was confirmed by experimental testing. Since the proposed method does not require installing sensors or search coils within the motor, such a method is more appropriate for practical applications and improving the cost-performance in online condition monitoring. In addition, with some specific modifications, the suggested concept becomes useful for fault detection in other rotating machinery types. [ABSTRACT FROM AUTHOR]

This paper proposes a novel spoke-type permanent magnet (PM) machine, which adopts asymmetric modular consequent-pole (AMCP) rotor to enhance the effective PM flux due to the increased flux-focusing effect and reduced leakage flux and to improve the flux-weakening capability due to the increased d-axis inductance. Moreover, the pole-shaping method based on three sectional arcs is proposed to suppress the harmonics of airgap flux density. Since the rotor structure is relatively complex, the finite-element analysis together with multiobjective genetic algorithm is adopted to optimize this design. Furthermore, the electromagnetic performance of the spoke-type PM machine with the proposed AMCP rotor (Spoke-AMCP), including the open-circuit airgap flux density, phase back electromotive force, torque, PM utilization ratio, efficiency, and flux-weakening capability, are compared with two conventional spoke-type PM machines with evenly distributed and alternate flux barriers (Spoke1 and Spoke2) and consequent-pole spoke-type PM machine (Spoke-CP). It is demonstrated that the Spoke-AMCP machine obtains the largest output torque and PM utilization ratio, lowest torque ripple and similar efficiency compared to Spoke1, Spoke2 and Spoke-CP machines. Moreover, although the Spoke-AMCP machine has the largest PM flux linkage, it has slightly better flux-weakening capability than the Spoke1 and Spoke2 machines. Finally, a 12-slot/10-pole Spoke-AMCP machine is built and tested to verify the analyses. [ABSTRACT FROM AUTHOR]

In low-speed applications, variable-reluctance permanent magnet machines are often proposed due to their efficient use of magnet material and high torque density. This becomes even more important in large linear applications, where the translator is longer than the stator. Often, however, very low power factors are experienced by this class of machines. This paper proposes a V-shaped flux concentrated version of a consequent pole linear Vernier hybrid permanent magnet machine and compares it to a surface-mounted magnet variant. Using finite-element analysis validated by two laboratory prototypes, it is shown that the flux-concentrated version increases the airgap flux density, which potentially leads to an improvement in the force density and efficiency or can be used to increase the operating power factor. [ABSTRACT FROM AUTHOR]

In order to improve the torque density of the magnetic flux concentrated permanent magnet synchronous motor utilizing a ferrite permanent magnet, it is important to reduce the leakage magnetic flux flowing through the rotor core. For satisfying the robustness of the rotating body and improving the torque density, we propose a structure in which two types of cores with different shapes are cross laminated. The proposed rotor structure consists of a core with a bridge that is necessary to maintain the rigidity of the rotor assembly, and a rotor assembly by cross laminating the segment-type rotor cores necessary for minimizing the leakage flux as well as improving the torque density. The complex three-dimensional (3-D) magnetic circuit of the cross-laminated rotor assembly has been modeled as a two-dimensional (2-D) model on the mathematical basis of an equivalent magnetic circuit. Using the equivalent 2-D model, the design of the cross-laminated rotor shape and the electromagnetic characteristics were examined comprehensively. At the same time, mechanical stresses due to centrifugal force and torque transmission between rotor core and shaft were examined. Finally, after the prototype was fabricated, the analysis and design methods were verified through no-load and load tests. [ABSTRACT FROM AUTHOR]

Deformation of the windings is one of the main causes of the power transformers failure. Here, for the first time, the electromagnetic forces exerted on the windings are computed in ferroresonance condition and compared with that of the inrush current for a typical power transformer. In both cases, the magnetic core of the transformer saturates and the leakage flux around the windings increases, which leads to large forces on the windings carrying high currents. Therefore, precise modelling of the transformer core is required to calculate the forces inside the transformer. For this purpose, the Jiles–Atherton vector hysteresis model is employed in conjunction with finite element method (FEM) to simulate the laminated grain‐oriented steel core, and then the radial and axial forces inflicted on the windings are estimated. [ABSTRACT FROM AUTHOR]

This paper introduces a primary pad for wireless charging applications, which is able to transfer high power over large air gaps and is tolerant to lateral displacements suitable for electric vehicle charging applications. The developed pad is an improved solenoid designed specifically to address issues such as flux leakage and loss while retaining good coupling. It is a hybrid structure that consists of a combination of rectangular- or square-shaped coils and a central solenoid, all connected in series. When energized, it produces a single-sided, polarized flux similar to the flux pattern of the solenoid and double D (DDP) pads. The power transfer capability of this pad is investigated through finite-element analysis simulations. The results are compared first to a similar sized solenoid from which it was derived, and also a DDP primary pad and are verified through measurements on prototype systems in the laboratory. The aim of this paper is to provide an improved hybrid solenoid pad showing higher coupling factors and lower stray field emissions with a performance (coupling and stray field emissions) similar to that of DDPs. [ABSTRACT FROM AUTHOR]

High-temperature superconducting (HTS) transformers have a promising feature in reduction of total weight, total size, and the losses of large-scale distribution transformers. However, the lower leakage reactance of HTS transformers results in a higher short-circuit fault currents and electromagnetic forces. Therefore, optimization of short-circuit electromagnetic forces is one of the crucial aspects in the design of HTS transformers. In this paper, a novel analytical method is proposed for determination of optimum distributive ratios resulting in minimization of these forces for asymmetrical multi-segment windings of an HTS transformer. Employing these distributive ratios, radial and axial components of short-circuit electromagnetic forces in an HTS transformer are significantly reduced. Two- and three-dimensional (2D and 3D) finite element method (FEM) simulations are employed to verify the analytical method results. [ABSTRACT FROM AUTHOR]

The thin wobble motors that are required to hold rating shafts employ an electropermanent magnet. This turns the holding force on and off by applying a momentary electrical pulse. To design the magnet devices without the need for finite element analyses, a theoretical force model is necessary for predicting the attractive force. In this paper, first, a force model is derived by estimating the permeance around the air gap. A magnetic circuit is constructed, employing a relatively simple method to build the model in clouding leakage flux. Thus, the basic structure and driving principle are also presented. Next, an analytical force model is constructed on the basis of distribution parameter analysis between the stator and the rotating shaft. The design of the electromagnet core and the control method are presented. Finally, a prototype model of the motor that is 30 mm in diameter and 7 mm in thick is fabricated. The two models are verified by comparing the results of FEM with the results of the experiments. They can properly predict the attractive force, so the thin wobble motor with holding force can be applied in portable electric equipment.

This study proposes a two‐phase single‐air‐gap axial flux permanent magnet (AFPM) motor that offers a trapezoidal back‐electromotive force (EMF) waveform to improve the performance of the only‐pull drive technique compared with the radial flux PM (RFPM) motor. The only‐pull drive technique provides the benefit of allowing the use of thin magnets in the motor without suffering from irreversible demagnetisation. In the proposed motor, the design geometry is primarily considered to achieve the desired trapezoidal shape of back‐EMF. The effects of the geometry are explained with the help of air‐gap flux density, flux linkage, and the leakage flux. Both the radial flux and the proposed motor adopt the same design concept and hold equal electromagnetic loadings. The profile of back‐EMF and the electromagnetic torque driven by the only‐pull drive technique are compared with that of RFPM motor with non‐trapezoidal back‐EMF. Furthermore, the split configuration is proposed for the AFPM motor to reduce torque ripples. The demagnetisation analysis is performed to confirm the operating point of the magnets in a split‐AFPM motor. The results reveal that the AF motor is a good candidate for the only‐pull drive technique. [ABSTRACT FROM AUTHOR]

Power transformer, as one of the most important apparatus in power system, must be protected against the turn-to-turn faults. Although the various methods based on the terminal currents and/or voltages have been presented for transformer protection, the flux-based methods can be used to achieve the more accurate, sensitive, and secure results. Since the symmetrical form of the magnetic flux distribution will be disturbed due to any fault occurrence in the transformer windings, it can be considered as an appropriate criterion to achieve a suitable protection algorithm, which can detect the fault occurrence and identify the faulty phase/region. In this paper, a new leakage flux sensor is introduced and then a flux-based technique is proposed to detect and identify the faulty phase in transformers to apply in online conditions. By using the proposed technique, the faulty region can be identified in offline conditions, as well. The experimental results (which are done on a distribution transformer) show that this technique is secure in the face of overfluxing and transformer energizing conditions and can detect turn-to-turn faults with high sensitivity. Moreover, tap changer operation, imbalanced loads, and/or unsymmetrical voltage sources cannot influence the proposed technique security. [ABSTRACT FROM PUBLISHER]