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Soil resistivity is the key parameter influencing resistance and potential distribution on the soil surface for grounding systems and electrodes for HVDC power transmission. The paper presents a novel approach that does not rely on analytical expressions or simplifications inherent in the Wenner and classical characterization methods for obtaining a layered soil model. The new method and corresponding computational tool are implemented as an iterative process using a finite element method coupled with a numerical parameter estimation solver. The novel method is applied on soil with a very thin and highly resistive surface layer compared to a resistivity of a lower layer, where accurate implementation of the classical method would require Wenner measurements for short electrode spacings a. Since the classical characterization methods rely on the assumption that the electrode driving depth b is much smaller than a, it is practically (physically) impossible to drive the electrodes to sufficiently small depth b. The application of the novel method and a comparison with the classical approach are presented on examples including normal soils, one hypothetical soil with a thin highly resistive surface layer, and one experimental desert location. The application of the proposed method leads to an extreme increase in the characterization accuracy for the case of ideal two-layer soil with thin high resistivity topsoil justifying considerable computational time. [ABSTRACT FROM AUTHOR]

When overhead ground wire (OGW) is struck by lightning, the damage or rupture accident occur. This is unacceptable for the stable operation of the power system. Therefore, the investigation on the lightning-induced damage mechanism of OGW is significant for the optimization of lightning protection measures. Combined with the structural characteristics of OGW, this paper evaluated the thermal ablation damage of OGW caused by lightning strike, which provided the data support for the damage mechanism research. Firstly, the magnetohydrodynamics (MHD) models based on OGW and plate structure were established. The current density distributions as well as the arc root radii of OGW and plate under lightning strikes were compared. The thermal ablation damage model of OGW was also established. The influence of arc root radius on thermal ablation damage evaluation of OGW under continuing component of lightning current was analyzed. The results show that the arc root radius of lightning striking OGW is reduced by at least 50% compared with that of lightning striking plate. When using arc root radius of OGW for modeling, the results of the thermal ablation damage model are consistent with the reported experimental results. The maximum error is 9.80%. While the arc root radius of plate is adopted, there is an obvious difference between the thermal ablation damage model and the experimental results. The maximum error exceeds 20%. Therefore, in the numerical modeling of thermal ablation damage of OGW, it is necessary to consider the influence of structural characteristics of OGW on arc root radius. [ABSTRACT FROM AUTHOR]

In order to reduce the cogging torque of a symmetrical V-type line-start permanent magnet synchronous (LSPMS) motor, this paper proposes a multi-objective optimization method based on the combination of design parameter stratification and response surface methodology (RSM). The optimal solution to the RSM model is acquired using the max–min ant algorithm. The permanent magnet width, pole opening angle, stator slot width, rotor axial length, and rotor tooth width are selected as optimization variables. The cogging torque and average torque are the optimization objectives. Finite element method (FEM) results show that the cogging torque is reduced by 71.5%, the torque ripple is reduced by 65.6%, and the average torque is improved by 12%. Finally, the effectiveness of the algorithm is verified with simulation results. [ABSTRACT FROM AUTHOR]

This paper concerns the human feet resistance estimates in safety studies of earthing systems, taking into account small effective thicknesses of the surface layer and mutual resistance between the feet. Based on simulations using the finite element method, performed to determine the variation of the feet resistance to earth with the following parameters: resistivity of natural soil, surface layer resistivity and thickness, and separation distance between the feet, the available literature was analyzed; then, expressions for the surface layer derating factor based on the one-foot model are suggested that best match the simulation results. Simple correction factors are also proposed for calculating the earth resistance of two feet in parallel and in series that take into account the mutual interference of the feet for different separation distances between the feet. The influence of inaccuracies in feet resistance assessment on estimates of permissible prospective touch and step voltages is discussed in various cases, taking into account that resistance of the human body depends on the applied voltage and current path. [ABSTRACT FROM AUTHOR]

This paper is the first that proposes an extended hybrid analytical method (HAM) based on a two-dimensional (2-D) coupling between the semi-analytical Maxwell-Fourier analysis and finite-element method (FEM) in polar coordinates. The proposed model is applied to any rotating electrical machines. The main objective of this paper is to establish the magnetic field solution in the whole machine by coupling an exact analytical model (AM), proposed for all regions having relative magnetic permeability equal to unity, with a FEM in ferromagnetic regions. The AM and FEM are coupled in both directions (r , θ) in the edge separating teeth regions and all its adjacent regions by applied boundary conditions (BCs). The developed HAM gives accurate results on the magnetic flux density distribution and the cogging torque whatever the operating conditions, the magnetic or geometric parameters. All results obtained give very satisfactory agreement with 2-D finite-element analysis (FEA). [ABSTRACT FROM AUTHOR]

High voltage high-frequency (HVHF) transformers have a crucial part in the realization of high voltage direct current (HVDC) isolated power supplies. Nevertheless, they are the bulkiest component in the system besides being one of the major contributors to the power losses. Special care is therefore required to design HVHF transformers. The main objective of this paper is to design and implement a high voltage (10 kV), high-frequency (50 kHz) center-tapped transformer with high efficiency, small size, and low cost. The proposed transformer is designed as part of a 100 kV, 10 kW DC/DC converter for supplying power to a particle accelerator. The proposed transformer steps up the input voltage (500 V) to 10 kV. Then, a five-stage full-wave Cockcroft–Walton voltage multiplier (CWVM) is used for boosting the voltage to 100 kV. A detailed step-by-step design guideline for designing an HVHF transformer is also presented. To reduce the transformer's parasitic capacitance, the secondary windings are wrapped in segments. This taken approach has been illustrated in the paper and later verified through finite element analysis (FEA). The FEA analysis shows that the transformer parasitic capacitance has reduced significantly. Following the presented design guideline, the implemented prototype transformer has been built and later tested with a single-stage CWVM. The experimental results demonstrate that the prototype transformer has successfully met the design requirements including the small size, less weight, and low-cost objectives. [ABSTRACT FROM AUTHOR]

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]

This paper presents a two-dimensional analytical model for brushless double-rotor flux-switching permanent magnet machines (BDRPFSPMM) with yokeless stator recognized as a type of partitioned-structure flux-switching permanent magnet that is an appropriate machine to be employed as the electric motor in industry. The most salient advantages of the proposed machine are low iron loss due to volume of iron in stator and high space of stator slot for winding. The radial and tangential components of the magnetic flux density due to permanent magnets and armature currents in each active domain of the machine, electromagnetic torque, self- and mutual inductance, unbalanced magnetic force (UMF), and local traction are calculated based on the subdomain method. Teethes on both rotor and stator structures are effective on magnetic quantities, so interactions of rotor and stator saliency are considered. The method is general for the magnetic field calculation with any combination of rotor- and stator-pole number. To validate the proposed model, the analytical outputs are compared with those obtained from the finite element method (FEM). [ABSTRACT FROM AUTHOR]

Estimating losses accurately for magnetic materials in power conversion circuits is a challenging task. Solving the partial differential equations in a complex geometry of inductive components such as filter-integrated transformers is an additional prominent challenge. While there are some commercially available finite element simulation tools that provide loss calculations in time-domain for multi-dimensional geometries of magnetic materials, the principle of analysis is not fully disclosed and less flexible for engineers to use. In this paper, we introduce a comprehensive method for systematically and flexibly applying time-domain dynamic loss equations to geometric finite element methods in multi-dimensions. The developed post-process framework for magnetic core loss calculations is coded in an open-source programming language, Python, and verified by comparison with analytical solutions for a filter integrated isolation transformer under a variety of operating conditions. Parallel processing is used to deal with the large datasets associated with element-by-element numerical calculations in the time domain. A high level of accuracy is achieved and verified. [ABSTRACT FROM AUTHOR]

The permanent magnet electrodynamic suspension (PMEDS) owns the promising application prospect, due to its simple structure, low cost and reliable load capacity. However, the underdamping of the PMEDS system is still a challenge in engineering applications of transportation. This paper proposes a passive damping method and its implementation structure to improve the underdamping characteristics. This method utilizes the inherent magnetic leakage of on-board magnets technically. The principle of passive damping and its implementation structure is introduced in detail. And the kinetic models of ordinary and improved structure are established based on the topology graph. Besides, the magnetic field and the electromagnetic force involved in the kinetic models are analyzed, and the numerical analysis method of the drag force is verified by the high-speed test rig. Furthermore, the performance of passive damping is verified by finite element method (FEM) and the time-domain response analysis. The results show that the improved damping structure can effectively suppress vibration and improve the dynamic stability of the PMEDS system. It is beneficial to the engineering application of the PMEDS in the future. [ABSTRACT FROM AUTHOR]

The estimation of armature reaction is of great importance in the design and operation of synchronous machines. This paper proposes a new method to reduce quadrature armature reaction in salient-pole synchronous generators. The proposed method is to reduce the quadrature axis synchronous reactance of a salient-pole synchronous generator by novel flux barrier to the rotor poles. Finite element analysis by Maxwell software was used to evaluate the nonlinearity of the synchronous reactances and to obtain the result that the quadrature axis synchronous reactance decreases when the flux barrier is introduced into the rotor pole of a salient-pole synchronous generator. As part of the study, a new flux barrier was introduced and experimented on the rotor pole of a 50 kW, 4-pole salient-pole synchronous generator without damper winding used for diesel generator. [ABSTRACT FROM AUTHOR]

This paper presents an electrical endurance design method of multi-operation isolators using semi-physical simulation via algebraic multigrid iteration (AMG). The mathematical model of Magnetohydro dynamics (MHD) is built by simultaneous equations of mass conservation, horizontal momentum, vertical momentum, conservation equation of ion energy, as well as electromagnetic equation. In addition, the physical properties of plasma medium in non-solid state, including thermal conductivity, electrical conductivity, dielectric density over temperature are used to dynamically update the coupled multi-physics. The established model can thus be solved via AMG, which is a fast iterative method for solving large-scale sparse normal equations based on geometric multigrid method. The finite element method (FEM) is likewise conducted under the various operating conditions to seek arc plasma temperature, the electric potential, electromagnetic distribution. The electrical endurance reliability can be reckoned using the maximum likelihood estimator of the desired shape parameters and scale parameters of Weibull's distribution, by integrating analogical semi-physical simulation. The physical experiment is carried out which involves electrical safety test, the withstanding voltage test, also called Hipot test or dielectric test, arc ignition test, resistance test. It proves that the proposed method can realize the endurance design of electrical equipment with high convergence efficiency and low residual error, and is especially suitable for the analysis under multiple working conditions. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of corrosion on the magnetic circuit's influence on the induction machine's magnetic characteristics. To achieve this objective, we initially evaluated the magnetic properties of the induction machine's magnetic circuit under both corroded and non-corroded conditions by analyzing hysteresis loops using a vibrating sample magnetometer. We systematically examined magnetic parameters extracted from these experiments, including saturation magnetic flux density, coercive field, remanence, and the squareness ratio. Subsequently, we employed the finite element method to scrutinize the magnetic behavior of the induction machine under both corroded and non-corroded conditions. The magnetic parameters obtained from the experiments were then incorporated into the model representing the induction machine's magnetic circuit. The results demonstrate that corrosion in the magnetic circuit significantly impacts the induction machine's magnetic behavior, ultimately leading to reduced machine efficiency. [ABSTRACT FROM AUTHOR]

In order to relieve the problem of bearing wear in high-speed permanent magnet generator, a semi-symmetrical double winding structure with the same number of poles is proposed in this paper. The coupling of the winding magnetic fields enables the rotor to be subjected to a radial electromagnetic force along the direction of overcome gravity, which could effectively extend the service life of the bearings. Firstly, the design principle of the semi-symmetrical double winding structure and the winding MMF are analyzed based on the AC machine winding theory, and the elliptical magnetic field characteristics of the harmonic winding are clarified. Combining the characteristics of order and frequency for harmonic magnetic field, the magnetic fields coupling mechanism of the double winding is revealed, and the analytic model of the power generation and radial electromagnetic force are determined. Secondly, based on rolling contact fatigue theory, the service life improvement of bearing by the double winding structure is certificated. In addition, the magnetic fields of double winding are decoupling calculated by using the finite element method, and the consistency of results between the theoretical analyses and the finite element calculations is determined. Finally, the calculation accuracy of the finite element analysis is demonstrated by experiments on the prototype. [ABSTRACT FROM AUTHOR]

The impulse grounding impedance of the tower grounding device affects the lightning trip-out rate of the transmission line. It is necessary to optimize the design of the grounding device for impedance reduction. In this paper, a finite element model for the impulse property of the grounding device is established. The thin-shell theory is introduced to solve the problem of mesh division singularity caused by excessive dimensional differences between the conductor sectional area and soil dispersion area. Physical quantities such as potential, electric field strength, and current density of tower grounding devices were analyzed, and the impedance reduction mechanism of the needle-shaped grounding device was obtained. A simulation study of the needle-shaped tower grounding device was carried out to obtain the effects of five factors related to the needling: position, number, distance, length, and angle on the impulse grounding impedance, as well as their optimal values. The results show that adding the needling at the end of a star grounding electrode branch can effectively reduce the impulse grounding resistance. The number of needling is not the more the better, and the unit length utilization is maximum when 2 needles are used. Changes in the length of the needling have a greater impact on the impulse grounding resistance relative to changes in spacing. When the spacing between the two needles is 2 m and the length is 5 m, it is appropriate to set the angle in the range of 30°–60°. The optimized design of the tower grounding device can effectively reduce the impulse grounding impedance. [ABSTRACT FROM AUTHOR]

This paper aims to propose a novel data-driven approach for exploring the partial discharge inception voltage (PDIV) of turn-to-turn insulation in inverter-fed motors. To this end, the gas discharge theory-based finite element method is investigated to simulate the state of turn-to-turn insulation, and a comprehensive database is established concerning the structural and environmental factors. Subsequently, a bisected deep belief network (BDBN), which combines with deep belief networks (DBN) and the bisection method, is proposed to explore PDIV. Specifically, DBN is designed to distinguish the discharge state of turn-to-turn insulation, and the testing applied voltage is adaptively adjusted to explore PDIV by the bisection method. The experiment result demonstrates the effectiveness and reliability of BDBN in exploring PDIV of turn-to-turn insulation in terms of precision. [ABSTRACT FROM AUTHOR]

Many optimization problems in electrical engineering consider a large number of design parameters. A sensitivity analysis identifies the design parameters with the strongest influence on the problem of interest. This paper introduces the adjoint variable method as an efficient approach to study sensitivities of nonlinear electroquasistatic problems in time domain. In contrast to the more common direct sensitivity method, the adjoint variable method has a computational cost nearly independent of the number of parameters. The method is applied to study the sensitivity of the field grading material parameters on the performance of a 320 kV cable joint specimen, which is modeled as a finite element nonlinear transient electroquasistatic problem. Special attention is paid to the treatment of quantities of interest, which are evaluated at specific points in time or space. It is shown that the method is a valuable tool to study this strongly nonlinear and highly transient technical example. [ABSTRACT FROM AUTHOR]

This paper deals with the development of the multilevel simulation model of wireless power transfer coil system. The main purpose of this approach is related to the design of verified simulation model, whose main capabilities are related to the optimization purposes of the operational characteristics of WPT system, i.e., self- and mutual inductance identification, transfer characteristic influence, quality factor influence and radiated emission performance investigation. For these aims, the simulation model of the WPT coil is presented within FEA (finite element analysis) software. The electrical circuit of the WPT system is designed in PSpice software, and relevant input–output electrical variables are then supporting the FEA model for higher accuracy compared to the physical sample. In order to validate the accuracy of the model, the comparison of the transfer characteristic of proposed experimental prototype of WPT system is realized. At the end of the paper, the evaluation of various geometric alternatives of coil's shielding is done in order to investigate its influence on the WPT performance. [ABSTRACT FROM AUTHOR]

Reliability in the supply of electricity depends on isolation from the electrical power system. Insulators are components that have the function of insulating and supporting the electrical grid. The design of electrical distribution network insulators can have a great influence on the distribution of the electric field over its surface. When there is a great intensity of electric field applied specifically in a location, there may be a greater chance of the development of a fault. An optimized insulator profile design can ensure that the network has better performance. In this paper, particle swarm optimization is applied to optimize the profile of an insulator of the conventional electric power grid, based on the electrical potential data obtained using the finite element method, defined in this paper as optimized finite element method. The component parameters are optimized to obtain a parametric model. The parametric model is evaluated and compared with the usually employed profiles to define an optimized design. The results show that the proposed method is a promising alternative for the design of electrical energy distribution insulators. [ABSTRACT FROM AUTHOR]

The paper discusses design methodology, constructional alternatives and calibration procedure of current sensor suited for high-power semiconductor systems operated at medium switching frequencies (industrial contact and contactless power chargers). Even there are several types of the sensor on the market, for medium frequency operation they usually exhibit problems with measured signal and its postprocessing. Proposed sensor is designed for a current up to 200 A and 120 kHz and is based on current transformer principle. Design procedure is focused on winding analyses and its impact on operational characteristics. In order to verify proper choice of magnetic core and windings distribution, finite element analysis have been provided to verify magnetization and saturation of sensor core. Consequently, the internal structure of the sensor and its construction is being described, while it is considered that the sensor is equipped with an electronic unit in a common housing. The electronic transducer evaluates the measured data and produces the digital output signals, which are easy to transfer even to a long distance. Prototype of constructed sensor has been undertaken to experimental measurements for given frequency range in order to evaluate quality factors and accuracy. At the end of the paper, the required process of calibration was provided through the evaluation of the algorithm required by digital logic of the sensor. [ABSTRACT FROM AUTHOR]

This paper proposes a design scheme for a wireless power transfer (WPT) system based on multi-relay coils to solve the power supply demand of 500 kV transmission line online monitoring equipment. The relationship between the operating frequency and the coil loss is established to analyze the influence of the number of relay coils and the coil distance on the transmission performance. The particle swarm optimization model is established with transmission efficiency as the optimization objective. The distribution spacing between coils, the working frequency, and the number of coils are optimized. Based on the equidistant arrangement of relay coils, an optimization scheme of non-equidistant arrangement is proposed. Under the condition of the same number of relay coils, the transmission efficiency of the system is increased by 20.56% and has been verified by experiments. In addition, finite element analysis software has simulated the surrounding high-voltage field strength of the WPT system added to the insulators. The results show that the insulators still meet the insulation standards. The simulation and experimental results show that the proposed scheme can effectively meet the power demand of high-voltage line monitoring equipment. [ABSTRACT FROM AUTHOR]

The permanent magnet claw pole machine (PMCPM) with soft magnetic composite (SMC) cores has shown better performance than the traditional transverse flux machine, and its performance can be improved by developing its stator with hybrid silicon sheet and SMC cores, and this kind of PMCPM is named as HPMCPM. Due to its complex 3D magnetic structure, analyzing its performance by using the traditional finite element method (FEM) is time-consuming. To overcome this constraint, this paper proposes a magneto-electric-thermal coupling network (METCN) model with bidirectional data transmission to calculate the electromagnetic performance and temperature distribution and the calculation results are verified by the FEM method and experimental measurement results. Compared with the 3D FEM, the proposed METCN method has the advantage of fast calculation speed and similar accuracy. [ABSTRACT FROM AUTHOR]

This paper proposes a new design for line-start operation of synchronous reluctance motors. In the past years, synchronous reluctance motors have been studied by many researchers. Due to high efficiency, they have gained increasing interest because in the synchronous operation, there is limited losses in the rotor. On the other hand, line-start operation of the synchronous reluctance motors is an important challenge that can make this type of the motors popular in many applications. However, line-start operation techniques should not considerably affect the steady-state characteristics of the motor. In the proposed design, the arrangement, size and shape of the rotor conductor bars are designed based on the rotor magnetic circuit difference between induction and reluctance synchronous motors. Complete assessment of the motor parameters are examined using finite element analysis. The proposed structure improves the starting characteristics of the motor. Moreover, power factor of the proposed motor is slightly increased in comparison to that of conventional line-start synchronous reluctance motors. The results obviously show effectiveness of the proposed line-start operation strategy for the synchronous reluctance motors. Finally, experimental verification are also included to confirm the finite element analysis results. [ABSTRACT FROM AUTHOR]

In this paper, three typical permanent magnet machines for All-Electric aircraft propulsion are designed, optimized and compared. Firstly, the necessary performances are determined based on the requirements of high power/torque density and an aircraft with a maximum takeoff weight of 1500 kg. The initial structures of interior permanent magnet (IPM) synchronous machine, vernier permanent magnet (VPM) machine and flux-switching permanent magnet (FSPM) machine are designed with identical stator outer radius and rotor shaft length. Then, parametric sensitivity analysis and multi-objective particle swarm are combined as an optimization methodology to optimize these machines. Based on the finite element analysis, the electromagnetic performances such as no-load airgap flux density harmonic spectrum, cogging torque, average output torque, losses, efficiency and power factor, etc., are generally compared and analyzed. Subsequently, the discussions are carried out, where the strength and weakness of these three machines are concluded and the future prospects are suggested. Finally, it is concluded that if effective measures are implemented to reduce the permanent magnet eddy current loss and improve the power factor, the VPM machine would be the most suitable choice among these machines for All-Electric aircraft propulsion. [ABSTRACT FROM AUTHOR]

As permanent magnet claw pole machine (PMCPM) is designed with a complex 3D magnetic structure, the 3D finite element method (FEM) is commonly used for its accurate performance analysis. However, using 3D FEM will consume a long time in the initial design stage. Its analysis time can be saved greatly by using the analytical method (AM) or equivalent magnetic circuit method (MCM), however, the obtained performance is not accurate and some performance even cannot be obtained if only one of these methods is used. To overcome the above constraints, this paper proposes a calculation method that combined analytical and equivalent magnetic circuit method (AMCM) to calculate the main electromagnetic performance of PMCPM quickly. Its calculated results are verified by corresponding results obtained by using the 3D FEM. It can be seen that the proposed AMCM is effective for calculating the main electromagnetic performance and designing of PMCPM. [ABSTRACT FROM AUTHOR]

Safety of electric power systems depends heavily on distribution of electric field in high-voltage switchgear. Switchgear failure can lead to fatal disasters in important systems. It is necessary to evaluate electric field and insulation performance for high-voltage switchgear in key systems. In this paper, considering a high-voltage switchgear system designed for nuclear power station, a three-dimensional finite element model is developed for the whole system. Distribution of electric field is simulated under different loads, including the specified voltage and the overload. The insulation property of the switchgear system is then evaluated. Experiment on the physical prototype validates the simulation evaluation. To make the electrical field well distributed and reduce peak value, method of orthogonal experiment is used for parameter design. Optimization and improvement are then proposed. The optimization results show that the reliability is improved and the electric field is well distributed. The numerical model is established on personal computer, while it is solved remotely on High Performance Computing Center. Corresponding modeling techniques and computing methods are provided in this paper. [ABSTRACT FROM AUTHOR]

The total electric field on the roof platform of buildings becomes a new and important indicator of the environmental assessment of HVDC projects. In this paper, the upper-stream finite element method is used to simulate and calculate the distribution characteristics of the total electric field on the roof platform of the flat-roofed building adjacent to an HVDC line, from the factors of material conductivity and three-dimensional structure. The results show that when the conductivity of the building is greater than 10−10 S/m, it can be regarded as an equipotential body with the ground. Therefore, when the field mill measures the electric field on the roof platform, the field mill can be connected to the building to achieve the purpose of grounding. Otherwise, additional appropriate grounding treatment is required. Moreover, the protrusions such as parapets and stairwells on the roof platform of the building have both distortion and shielding effects on the total electric field. The larger the area of the protrusions, the better the shielding effect, making the total electric field on the roof platform weaker. Therefore, when measuring the total electric field on the roof platform, to avoid the unpredictability of the measurement results of the field mill, the field mill should be arranged in the center flat area at least 2 m away from the protrusions. [ABSTRACT FROM AUTHOR]

In this paper, a variable reluctance generator with segmental stator utilizing an assisted DC field for variable speed applications is proposed. In this work, analytical design, magnetic field analysis, and Parametric Sensitivity Analysis of the proposed machine are presented. The stator of suggested configuration, in addition to the distributed phase windings, is included the distributed assisted dc field coils, which are responsible for producing an adjustable magnetic flux in the generator. The segmental stator, the controllability of magnetic flux and generated voltage are the prominent features of the presented generator. Maintenance-free and easy accessibility of each stator segment due to utilizing the segmental stator, and high reliability due to the absence of brush and winding on the rotor is other features of the proposed machine. Finally, the Field Analysis using the finite element method is performed to verify the analytical design and sensitivity analysis. The results obtained from the FE analysis confirm the analytical design and the controllability of magnetic flux and generated voltage for the proposed configuration. [ABSTRACT FROM AUTHOR]

This paper introduces a reliable approach based on start-up transient analysis using continuous wavelet transform (CWT) and ridges (local maxima in spectrogram) for early detection of a broken rotor bar fault in an induction motor. The main goal is to track the evolution of the fault frequency components related to rotor bar breakage in the starting current of the motor. The CWT has been used to limit the current signal to a specific frequency band (suitable for observing the dynamics of fault frequencies), and ridges in the time–frequency domain are computed to observe the fault feature related to rotor bar breakage. The suggested work's key benefit is the precise visualization of the fault feature in the time–frequency plane to detect the rotor fault. A quantitative analysis of fault severity has also been presented. A finite element model (FEM) of the machine is simulated in ANSYS 2D workbench to investigate the fault. The proposed method is validated with simulated data, and to demonstrate the efficacy of the method, various simulation scenarios with varying load torques have been presented. Finally, the diagnosis approach is validated using an accessible public data set corresponding to the aforementioned fault. [ABSTRACT FROM AUTHOR]

Thermal stresses on the induction machine are the main cause of reliability reduction, which can lead to further faults in the machine. Using the thermal sensors to determine the temperature of the electric machine is costly and difficult; therefore, indirect methods have been considered to this end. One of these methods is utilizing the thermal model of the induction machine, which can determine the temperature of various parts of the motor without requiring any additional circuits for signal injection or the use of rotor resistance estimation techniques. This paper presents a modified thermal model of the induction machine. In this model, each rotor bar's current is designated as a heat source. Therefore, to solve the new model, it is required to calculate the rotor bars' current. The currents of the rotor bars of a squirrel cage induction motor are calculated by using the motor terminals data measured with an experimental test setup and both winding function and finite element methods. Then, the losses of the rotor cage are obtained by these currents. By inserting these losses into the modified lumped parameter thermal model of the machine, the rotor temperature will be determined. The results have been validated by analyzing the motor temperature with MotorCAD software, and it has been observed that the new proposed model achieves more accuracy compared to the conventional model. In addition, the accuracy of MotorCAD simulation was confirmed by implementing a temperature sensor in stator winding and comparing the achieved temperature with MotorCAD simulation results. [ABSTRACT FROM AUTHOR]

In this paper is presented a two-dimension analytical model for linear permanent magnet inner armature double-sided synchronous motors (LPMIADSSMs). The flux density in all areas of the proposed machine is calculated based on the sub-domain method. According to this method, the machine areas are divided into eleven sub-regions such as first external, first mover, first PM, first air gap, first winding, stator, second winding, second air gap, second PM, second external and second mover, which sign as FE, FR, FP, FAG, FW, S, SW, SAG, SP, SE and SR. To find the flux density equations, it is mandatory to solve the extracted Maxwell equations and apply the boundary conditions between each two sub-regions, which lead to find the unknown coefficients for flux density in each sub-region. In addition, the influences of magnetization patterns, i.e., parallel, ideal Hal Bach, 2-segment Halbach and bar magnet in the shifting direction of the flux distribution and armature reaction (AR), are investigated. To validate the obtained results, the proposed model results are compared with those obtained from finite element method (FEM) and Maxwell software. [ABSTRACT FROM AUTHOR]

Part of power transformers failures are result of great electromagnetic forces acting on its windings due the circulation of high currents, as in case of short circuits. To contribute for a more reliable mechanical design, this paper presents a finite element analysis (FEA) for a complete calculation and evaluation of electromagnetic forces on transformers windings. Three arrangements of concentric windings are analyzed considering three-phase and three-dimensional models, dealing with issues as the influence of magnetic core window and lateral phases presence, ensuring more accurate results. The adopted modeling allows to determinate the total axial and radial forces on all the phases and its distribution over the height of windings and around the core leg. It was possible to identify points of greater and lesser forces and the behavior of forces on different constructive arrangements, allowing its choice improvement during the design stage. The results present good agreement to the analytical method, allowing the application of the developed FEA for transformer design optimization, contributing for a time and costs reduction and avoiding future mistakes in its construction and failures during its operation. [ABSTRACT FROM AUTHOR]

Coreless fault current limiter with variable series reactor is an emerging technology for limiting the amplitude and shortening the fault duration in the power network with simple and reversible operation. The device includes two coaxial, coreless reactors with axial mobility to vary and increase the effective inductance of the network during the short circuit fault. The reactors are automatically returned back to their initial position after the fault is cleared, with minimal net inductance. This paper aims to analytically describe the electromagnetic theory and validate the functionality of the device. For this purpose, the resistance and inductance of the device are first computed at normal condition via the basic theory of engineering electromagnetics. Next, the respective electromechanical performance characteristics such as force, positional displacement of the reactors, and the effective inductance are calculated at the faulty condition. For verification purposes, analytical results are compared against the finite element model. [ABSTRACT FROM AUTHOR]

The effective insulation design of the stress grading (SG) system in form-wound stator coils is essential for preventing partial discharges and excessive heat generation under pulse-width modulation excitation. This paper proposes a method to find the optimal insulation design of the SG system aimed at reducing the dielectric and thermal stresses in the machine coil. The non-uniform transmission line model is used to predict the voltage propagation along the overhang, SG, and slot regions considering the variation in the physical properties of the insulation layers. The machine coil parameters for different insulation materials are calculated by using the finite element method. Two optimization algorithms, fmincon and particle swarm optimization (PSO), are applied and compared to find the optimal thickness and material properties of each insulation layer as well as the length and location of the SG system. The results under different rise-time excitation show that the optimized geometry by using PSO can produce a higher reduction in the dielectric and thermal stresses, as well as in the maximum overvoltage along the machine coil than the original geometry and the optimized geometry using fmincon. The machine coil model is validated by means of comparisons with experimental measurements. [ABSTRACT FROM AUTHOR]

In this paper, an equivalent circuit model of electro-mechanical converter (EMC) is developed using Cauer circuits, which can be used to improve the response speed of high-speed switching valves (HSVs), and this model can replace the transient analysis method of finite element model with high computational cost and the traditional magnetic circuit model that cannot accurately reflect the eddy current and skinning effect of coils. For EMC with high-frequency operation, the Cauer circuit can be used to describe the eddy currents on the physical layer and the skinning effect of the soft magnetic material. In this paper, a multi-field coupled EMC trapezoidal circuit simulation model is developed, and the reliability of the model is verified by experiments. The model can be used to analyze the energy consumption in order to identify the main optimized components of the EMC, and the genetic algorithm is selected as the optimization method to improve the structure, which leads to the reduction of eddy current losses and the improvement of the overall dynamic response of the EMC. [ABSTRACT FROM AUTHOR]

No-load losses are caused by the magnetizing current that needed to energize the transformers core. These losses are constant and occur 24 h a day, regardless of the load. So, the customers should pay the fixed monthly cost for these losses. In recent years, amorphous alloy has been used to improve distribution transformers performance with the decrease in No-load losses and the increase in the efficiency of transformers. This paper outlines the 2605SA1 amorphous core as a new development of the amorphous alloy with a higher saturation induction. This paper presents a comparison between traditional distribution transformers and amorphous distribution transformers. Distribution of flux density in two different transformers with amorphous core and M5-type silicon steel core has been simulated using 3-D finite element modelling. The simulation and modelling results have been compared with the tests results of 630 kVA, 34.5/0.4 kV prototypes manufactured in the TEK TRANSFORMER factory in Turkey. A good agreement has been obtained between the simulation and experimental results. The simulation and test results show that amorphous core considerably (about 63%) reduces the no-load power losses as well as efficiency of transformers. [ABSTRACT FROM AUTHOR]

In traditional wireless power transfer (WPT) system, the output power and efficiency of the system decrease sharply when there is an angular misalignment between the transmitter and receiver. To solve this problem, this paper proposes an omnidirectional WPT system based on the tripolar pad to power up electronic devices, which can realize multiple degrees-of-freedom wireless charging. Firstly, the circuit model of the omnidirectional WPT system based on tripolar pad is established with LCC compensation network, the expression of output power is calculated, and the effect of cross-coupling between transmitting coils on the system is analyzed in detail. Through finite element analysis (FEA) simulation with ANSYS Maxwell, the expression of mutual inductance with rotation angle is fitted, which proves that the output power is independent of the rotation angle. Besides, it is found that the tripolar pad can generate a rotating magnetic field, which enables the receiving coil to pick up magnetic energy under an arbitrary angular misalignment. Then, considering the requirements of practical application, the design method of the proposed omnidirectional WPT system is given. Finally, a 100 W experimental prototype is set up to verify the effectiveness of the proposed WPT system. The output power fluctuation is within ± 8.7%, which verifies that the output power is independent of the rotation angle. [ABSTRACT FROM AUTHOR]

In this paper, the authors propose a flexible automatic procedure for optimizing multiphase single-layer winding end-connections by the differential evolution algorithm. By using the winding distribution in slots as a predefined input, connections between phase conductors located in different slots are determined to minimize the winding average coil pitch and to simultaneously maximize the number of coils with identical coil pitch. For an adopted geometrical shape and number of turns of individual coils, minimization of winding average coil pitch results in minimized end-connection length, winding resistances, end-leakage inductances, winding mass and copper losses, while machine efficiency and power factor are maximized. However, maximizing the number of identical coils simplifies and speeds up the process of coil fabrication during machine assembly, but potentially leads to higher average coil pitch. The proposed method is applied to single-layer windings with different slot, pole and phase combinations, where it is proven that the method automatically provides end-connection arrangements which are better or equal in terms of copper usage and simplicity of fabrication than the ones found in the literature. Verification is conducted by comparing overall performance of several Rotor Permanent Magnet Flux Switching motors with different stack lengths, outer diameters and optimized end-windings by means of 2D finite element analysis and 3D analytical approach. The proposed method is conceived as an automatic tool for optimization of single-layer winding end-connections during comprehensive electrical machine design optimization. [ABSTRACT FROM AUTHOR]

Different environmental conditions such as pollution, rain, and frost affect the performance of polymeric insulators. In cold climates, insulators may become frozen, resulting in non-uniform distribution of potential and electric field around the insulator. Non-uniform distribution of potential and electric field along the insulator in turn cause problems such as erosion and flashover. Also, due to the wind direction in cold regions, the pollution layer accumulates non-uniformity on the insulator surface. This paper investigated the effect of ice layer with different configurations in combination with ring-shaped contamination, which is more common in cold regions, on the insulator surface to obtain the electric field distribution and leakage current of a 20 kV polymeric insulator. For this purpose, software based on finite element method (FEM) was used. Experimental test for evaluating the leakage current analysis of ring-shaped polluted insulator under ice condition was done in a laboratory clean fog chamber. The results of experimental data and the proposed simulated models were compared and validated. The results revealed that parameters such as increasing the freezing layer and its intensity, continuity of the freezing structure and electrical conductivity of the ice layer would enhance the amplitude of the electric field and leakage current, increasing the probability of flashover. Also, in the combination of ring-shaped contamination layer and freezing, the parameters of the ice layer are more influential than the contamination layer on the electrical behavior of the insulator. [ABSTRACT FROM AUTHOR]

In this paper, a finite element analysis (FEA) based fast optimization method to optimize a lightweight in-wheel switched reluctance machine is presented. This method speeds up the switched reluctance machine optimization procedure by running the FEA simulations with single-phase constant current excitations for half electrical cycle and estimating the machine performance metrics using the gathered FEA data. Hence, the machine's dynamic performance estimation process takes shorter for each design candidate. The optimization algorithm employs designs of experiments (DOE), response surface (RS) analysis method, and differential evolution algorithm (DE). Here, the DOE method is used to reduce the search space by narrowing down the upper and lower boundaries of each design variable based on the RS analysis. Although this process does not guarantee getting the Pareto front, it places the search space close to the actual one. Hence, the multi-objective DE optimization finds the Pareto optimal solution set without requiring a large number of iterations as well as a large number of candidate designs for each iteration. The method is applied to a 24/16 SRM that is intended to be used in a lightweight race car as a hub motor. Six dimensionless geometric variables are optimized to satisfy three objective functions, namely torque ripple, motor mass, and copper loss. While the conventional DE takes at least 3000 candidate designs, the proposed method considers only 559 designs to reach a similar Pareto front. It is observed that the proposed method takes about 6 h 30 min compared to the conventional method that takes 32 h 50 min using the same computer. Therefore, the computation time is reduced almost five times with the proposed method. [ABSTRACT FROM AUTHOR]

This paper analyses the impact of the number of stator slots to rotor bars, i.e. the slot combination, in a cage rotor induction motor (IM) on its electromagnetic torque ripple during steady-state conditions. The study is focused on a conventional low voltage, eight-pole, three-phase, mains-fed IM design. To adequately evaluate the torque ripple magnitude, a 'torque ripple factor' is introduced and numerically calculated. To this end, IM behaviour in two common eight-pole stator slot number geometries is examined using numerical models, where, for each examined stator geometry, operation with a range of different rotor bar numbers used in practical IM designs is evaluated. For the sake of completeness and cross-validation, two different modelling approaches are used: a recently reported low-computational intensity winding function-based model and a commercial finite element analysis electromagnetic modelling software package. The paper findings deliver a detailed insight into the impact of rotor bar number, whether skewed or otherwise, on the motor steady-state torque ripple level. The presented results are indicative of the fact that the number of rotor bars only, and not the slot combination, is the dominant factor that influences the electromagnetic torque ripple in IMs with skewed rotor bars. [ABSTRACT FROM AUTHOR]

This paper presents the optimal design and performance analysis of a novel synchronous reluctance motor with outer rotor for determination of the effect of the rotor pole shape on the machine's performances. The investigation has been made in order to find the possible ways to improve the power factor with refining the rotor geometry without using permanent magnets. Starting from the design of the machine with classical rotor pole that was implemented in FLUX 2D, a finite element analysis software coupled with an optimal design procedure implemented in MATLAB was performed. The purpose of this complex co-simulation was to obtain several outer rotor structures that increase the performances of the machine: saliency ratio, power factor and torque density. For the proposed structures, especially for the modular topology, the obtained results of saliency and power factor have never been presented in the past literature. Hence, this represents a useful starting point for the following analysis of outer rotor synchronous reluctance machines with improved power factor. [ABSTRACT FROM AUTHOR]

In this paper, a high-efficiency wireless power transfer (WPT) system based on magnetic resonant coupling is designed to operate at low frequency for electric vehicle charging. For simplicity, two coils wireless power transfer is proposed. Transmitter and receiver coils of WPT system are designed to improve quality factors and coupling coefficient. Effect of turns, coil radius, and misalignment on coil parameters and system performance are analyzed using three-dimension finite element method. Compensation circuit is designed and analyzed to achieve maximum power transfer efficiency. The effect of coupling coefficient value on system efficiency and resonance frequency is investigated. Input power, output power, and compensation capacitors voltage stress of the two compensation methods are analyzed and compared. Finally, the system performance is tested under different spacing and misalignment. Power transfer efficiency is more than 95% even under misalignment. [ABSTRACT FROM AUTHOR]

Double-turbine systems offer a higher capability of wind energy conversion compared to single-turbine systems. Therefore, in order to improve the performance of double-turbine systems and eliminate mechanical gearbox systems by utilizing the direct-drive concept, a new direct-drive generator design is required. In this paper, the structure of a novel spoke-type permanent magnet induction generator (STPMIG) exploited in double-turbine wind systems is investigated, and the performance and relationships of the proposed generator with and without iron bridges are studied. The proposed generator consists of a stator, and two concentric permanent magnet and squirrel-cage rotors, in which the voltage induction in the stator windings is possible only by the permanent magnet outer rotor. Although utilizing the permanent magnet rotor with iron bridges enhances the mechanical strength, the leakage flux increases, which leads to the reduction in the generator output power. In order to decrease the leakage flux and improve the output power of the proposed generator, the bridgeless outer rotor structure is preferred over the rotor with iron bridges. The bridgeless structure offers lower leakage flux, higher efficiency, and lower voltage regulation in comparison with the bridged structure. Furthermore, the novel structure of double-rotor STPMIG allows rotors to rotate independently at different speeds without employing additional rings and brushes, regarded as considerable merit for double-turbine wind systems. Finally, a 250-W bridgeless double-rotor STPMIG exploited in double-turbine systems is constructed and tested to verify the finite element analysis (2D-FEA) results. [ABSTRACT FROM AUTHOR]

This paper presents a simple turn-on and turn-off angles adjustment method to increase the efficiency of small-size switched reluctance motor (SRM) in wide speed and torque range. The simplicity of the control algorithms allows building a variable speed drive without a high-performance microcontroller and FPGA or ASIC. The firing angles calculation uses a second-order polynomial and look-up table. An increase in efficiency is demonstrated on the finite element analysis (FEA) model of SRM which was verified against measurement on an experimental test bench. Measured efficiency maps have a flat top for the investigated motor. Therefore, the angle jittering due to limited position sensor precision and 50 µs processor cycle time have a small impact on motor efficiency. The evaluation of the angle adjustment method and comparison with measurements identifies which part of the FEA model is crucial for the one-to-one implementation of the angle adjustment formulas obtained from simulation to the motor control algorithm. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of different magnetization patterns in the performance of three-phase permanent magnet synchronous motors (PMSMs). Three magnetization patterns widely used in surface-mounted PMSMs are radial magnetization, parallel magnetization and Halbach magnetization. In this paper, these magnetization patterns are applied to 9-slot/10-pole and 12-slot/10-pole surface-mounted PMSMs. The electromagnetic characteristics and performance of the motors such as air gap flux density distributions, phase back-emf, cogging torque, unbalance magnetic force and output torque are intensively evaluated in 2D finite element method. Important findings indicate that PMSMs with ideal Halbach magnetization exhibit almost zero cogging torque and sinusoidal phase back-emf waveform. Parallel magnetization and radial magnetization yield more trapezoidal phase back-emf waveform which results in higher torque ripples. One way to minimize the torque ripples is by reducing the higher-order harmonic components in the phase back-emf waveform which can be achieved with the best value of magnet pole arc. Additionally, a potential cost saving can be realized since the motor has smaller magnet volume as being demonstrated in the case of 9-slot/10-pole, three-phase surface-mounted PMSM in this paper. [ABSTRACT FROM AUTHOR]

In this paper, gradient-based optimization methods are combined with finite-element modeling for improving electric devices. Geometric design parameters are considered by piecewise affine parametrizations of the geometry or by the design element approach, both of which avoid remeshing. Furthermore, it is shown how to robustify the optimization procedure, that is, how to deal with uncertainties on the design parameters. The overall procedure is illustrated by an academic example and by the example of a permanent-magnet synchronous machine. The examples show the advantages of deterministic optimization compared to standard and popular stochastic optimization procedures such as particle swarm optimization. [ABSTRACT FROM AUTHOR]

Paper presents a mathematical model of the radial active magnetic bearing, which is indented for the simulation of the magnetic bearing dynamic response. The circuit model of the bearing is based on differential equations. The circuit model has incorporated results of magnetic field analysis, which led to the creation of the field-circuit model. Presented model of the magnetic bearing takes into account the necessary control system. The experimental results are presented to validate the proposed model. [ABSTRACT FROM AUTHOR]

Energy efficiency is primary target for electric motor designers. The Eddy current losses can cause deterioration of permanent magnet machines magnetic properties and increase rotor temperature. Therefore the rotor eddy current loses can decrease efficiency of permanent magnet brushless DC (PM BLDC) motors. Permanent magnets when designed with axial segmentation help reduce the eddy current losses. This paper presents an investigative study on calculating eddy current losses of in-wheel permanent magnet brushless direct current motors and the effect of segmented axial direction magnets on the efficiency of these motors used in light electric vehicle. In this study in-wheel PM BLDC motor has been designed and analyzed on with slot/pole combinations 24/20, 36/30, and 42/36, that the motor is rated power of 4 kW at rated speed of 1500 rpm. Finite Element Method (FEM) is used to carry out numerical analysis for an accurate result. The magnet losses and efficiency are calculated for segmented magnets with different quantity of magnets in the axial direction. Changing the number of axial magnet segment from 1 to 20 causes approximately 1% increase in the efficiency. Following the change in number of axial magnet segment, the shaft power values increment is about 40 W, while shaft torque is between 0.25 and 0.30%. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive degrees-of-freedom finite element method is extended to three-dimensional (3-D) nonlinear magnetic field analysis. The error distribution of the discrete solution changes along with the iterative process, and mesh coarsening or other operations with the same effect is needed to keep the scale of the problem small. In this proposed adaptive method, dispensable degrees of freedom (DoFs) are eliminated from the unknown list by constraining them with supplementary interpolation functions, which are formulated with master DoFs. Compared with mesh coarsening, the administration of DoFs and geometric data are no longer required, while the topology of the mesh is maintained. To extend to 3-D problems, a novel constraint, which produces accurate coefficients for an alterable number of master DoFs, is presented. The constraint is integrated into the element algebraic equation, followed by a conventional assembly. Other techniques for the adaptive algorithm are also included in this method. Several numerical examples are tested to showcase the effectiveness of this method in 3-D problems. [ABSTRACT FROM AUTHOR]