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Reducing motor losses is very important in connection with raising the requirements set by international regulations on reducing electricity consumption. As induction motors are increasingly powered by high-frequency voltage, core losses starting to play a dominant role in motor loss balance. The presented paper shows how to calculate the basic and additional losses in the core of the induction motor, generated by the reluctance and slot harmonics of the magnetic field in the motor and by the higher harmonics produced by the inverter, using analytical and field-circuit methods. The results for motor operation at frequencies of supply voltage 10, 20 and 350 Hz were presented and compared with the results of measurements. The main achievement is the statement that losses in the core of the motor fed from the inverter should be calculated as the sum of losses generated by individual harmonics both in the motor and generated by the inverter.

Smart bidirectional high-power electric vehicles charger can be based on Solid-State transformers (SSTs). A specific design of a low-cost smart charger is proposed using a medium frequency transformer based on a wound core made with Grain Oriented Electrical Steel (GOES) operating at medium frequencies and a temperature higher than coil ones. The preliminary study, based on core losses measurements made with rectangular and sine voltages, proves that the best case is the simplest possible converters producing rectangular voltages. Experimental investigations made on a smaller transformer of the same structure provide data for designing the 350 kVA transformer coils and estimating the efficiency.

The technologies of cutting the cores of electric machines change the magnetic properties and the loss of the electrical sheets used, affecting the machine’s parameters, mainly power losses and efficiency. This is particularly important in the case of induction motors, which are a significant consumer of electricity. Therefore, the problem of increasing their efficiency is important from the point of view of environmental impact. The article presents a method of approximating a material’s magnetic properties based on the results of measurements carried out with specimens of various widths. The presented method allows for an approximate representation of the changes in the structure of the material caused by the cutting technology. It is used in the analytical method for calculating motor parameters, and gives results that are in good agreement with the measurement. This method can determine the operating parameters of electrical machines of various sizes and rated powers.

Purpose The purpose of this paper is to present a comparison between reluctance synchronous machine-enabling work at high internal temperature (HT° machine) with laminated and solid rotor. Design/methodology/approach To obtain heat sources for the thermal model, calculations of the electromagnetic field were made using the Opera 3D program including effect of rotation and the resulting eddy current losses. To analyse the thermal phenomenon, the 3D coupled thermal-fluid (CFD) model is used. Findings The presented results show clearly that laminated construction is much better from a point of view of efficiency and temperature. However, solid construction can be interesting for high speed machines due to their mechanical robustness. Research limitations/implications The main problem, despite the use of parallel calculations, is the long calculation time. Practical implications The obtained simulation and experimental results show the possibility of building a machine operating at a much higher ambient temperature than it was previously produced for example in the vicinity of the aircraft turbines. Originality/value The paper presents the application of fully three-dimensional coupled electromagnetic and thermal analysis of new machine constructions designed for elevated temperature.

The method of cutting motor core sheets causes a change in their magnetic properties and core losses, especially additional losses. Reducing motor losses is very important because of the fulfillment of increasingly stringent requirements set by international regulations for reducing electricity consumption. Due to fact that more and more often induction motors are supplied with high-frequency voltage, core losses are beginning to play a dominant role in the motor’s loss balance. That is why accurate determination of these losses is very important and cutting has a significant impact on them. This report shows how the method of cutting sheet metal affects losses in the finished induction motor working in a wide frequency range. The paper presents the impact of various motor core fabrication technologies on its operational parameters and an approximate way of including this impact in analytical calculations at the design stage of new machine designs, as it is necessary to use sheet metal cutting technologies such as laser or electrical discharge machining (EDM) at the prototype stage. The proposed method is based on measurements of sheet parameters made on toroidal samples with appropriately selected dimensions, so that the width of the sample corresponds to the average width of the motor core elements.

This paper presents the core losses and performance characteristics of a small power induction motor with the core made from different electrical sheets, supplied from mains or PWM frequency inverter at 50, 100, and 200 Hz. Field-circuit and analytical methods are used for loss calculations, taking into account the nonlinear phenomena and additional core losses. In the calculations, the characteristics of mechanical losses measured against the speed for the motors and different electrical sheets magnetization, for frequencies up to 2000 Hz, as well as losses density characteristics against the flux density were used. The results show a significant increase in core losses concomitant with the motor load increase. In addition, analytical methods were used to calculate the performance characteristics versus load power. Calculated results were verified by measurements.

This paper presents a comparison of losses at no load and full load of six different induction motors which rated powers are between 3 kW to 280 kW. The results show that additional core losses are strongly dependent on the load of the motor. The reason is the saturation of rotor tips which leads to an increase of the effective slot openings and the strengthening of harmonic by the induced currents in rotor cage. That leads to significant increase in additional core losses concomitant with motor load increases. For loss calculations, field-circuit and analytical methods are used. Using the FEM is presented an in-depth analysis of the phenomena at no-load and load indicating the reasons for increasing losses at the load conditions. Additionally, improved analytical method was employed to calculate the curves of stray losses versus load power. The results for no-load losses, stray losses and efficiency are compared with the measurements and good agreement was obtained for both field-circuit and analytical method. The change of stray losses versus output power was compared with formula proposed by IEC 60034-2-1 standard. The assigned values of stray load loss were found to be generally lower than average test result for motor with rated power below 18.5 kW and generally higher for motors with bigger rated power. In situations where a fixed value of stray load losses may be required the obtained curves can be used.

Purpose The purpose of this paper is to determine the physical design parameters that influence the total resistance of a twisted conductor (cable). One of the physical parameters characterizing this type of structures is the uneven distribution of resistivity due to hardening, which is the result of stress exerted on the wires during the manufacturing process. Design/methodology/approach The authors have developed a method to take into account the effect of localized hardening on the inhomogeneous distribution of electrical conductivity in the distorted structures of the conductor. To achieve this goal, the authors have implemented a mechanical-electrical simulation method. The resistance characteristics have been measured as a function of mechanical stress. Findings As demonstrated by the results of measurements conducted on various samples and with various cable design parameters, the resistance of a given material (copper or aluminum), expressed as a function of stress, does not depend on the type of force applied. Therefore, the same characteristics may be applied to various cable designs. Practical implications The method presented in this paper enables more detailed investigation of the influence of particular design parameters on the total resistance of a cable. It also provides the ability to determine optimal settings of design parameters. Originality/value The approach is distinct from similar studies because it takes into account the deformed geometry of the conductor and the uneven distribution of the resistivity within a filament. In the literature, it is sometimes stated that the distribution of resistivity in a compacted cable is uneven, but its measurement is deemed impossible. This paper provides a method for determining such a distribution.

Purpose – The purpose of this paper is to present the distribution of the magnetic field and additional losses analysis of the induction motors (IM) with opened and closed rotor slots. Design/methodology/approach – In the field-circuit approach the distribution and changes of magnetic flux density in the motor are computed using a time-stepping finite element method. The additional losses in each element are evaluated at different frequencies. Findings – An approximate analytical formulation is derived for rapid losses computation confirmed by the results of field-circuit method. For high-voltage motors due to the size ratios of the core and relatively deep stator and rotor slots major role in causing loss of higher harmonics play a fundamental slot harmonics. Higher harmonics order bigger than 100 cause only small part of total higher harmonics core losses. Closed rotor slots construction influenced significantly on no-load losses mainly due to reduction of losses at slot upper part. For nominal load condition that influence is not so strong according to the saturation of slot tips by rotor leakage flux. Nevertheless, core losses at load are several times higher as at no-load. Research limitations/implications – In future research authors will take into account motors feed from PWM inverter, working in the frequency range up to 400 Hz. Practical implications – The results of investigation will be used in more detailed design of IMs especially for motors with closed rotor slots. Originality/value – The methods presented in the paper was not used before. Also results of additional losses in the motor core calculation, especially according motors with closed slots at no load and load conditions are new.

In this paper we propose a new method using finite elements modelling to predict the impact of stranding and compacting process on a conductor electrical resistance. The experimental work has highlighted the complexity of physical phenomenon within the conductor caused by elastic and plastic deformations and inters-strands electrical contact resistance. In reality, electrical performance of a conductor depends on the nature of the material and its metallurgical state, on the me- chanical pressure and electrical conductance of inter-strands contact areas. For these reasons, mechanical models have been developed in Abacus software to study different parameters involved in the stranding and compacting process to determine the actual conductor shape, strands actual deformations, residual stresses and contact pressure, etc. The deformed geometries were exported to COMSOL Multi-physics software using ECAD IMPORT module. DC simulations were, then, performed to analyze the electrical resistance of the conductor. Finally, the results obtained by simulation have been compared to the measurements to determine the accuracy of the models.

PurposeIn the majority of devices for measuring the resistance of wires or cables, the supplying voltage is applied via some clamping arrangement. Thus, current enters the bundle of conductors through the side surface of the outside wire. The purpose of this project was to establish the distance from the supplying point after which the current may be considered to be uniform and normal to the cable cross‐section.Design/methodology/approachWhen current passes from one wire to another, the crucial parameter is the resistance of the contact region. The paper presents a method by which this region can be identified and relevant resistance measured. A comprehensive simulation was conducted for different types of wires and cables to assess the influence of design parameters on the current distribution and uniformity.FindingsThe distance from the current entry point (the clamps) to the position where current density may be considered uniform has been established. This has facilitated estimating recommended positions of voltage taps with reference to current taps.Practical implicationsThe look‐up tables and graphs allow adjustments to the position of the taps and/or correction of the measured results.Originality/valueThe original contribution of this paper is in the way the contact region is identified where current passes from one wire to another. Original relationships have been proposed showing the relationship between contact resistance and the design parameters of the cable and mechanical stress.

The paper presents the simulations of influence of a shaft of induction motors on the magnetic field distribution and the resultant magnetizing current. Motors are supplied from mains at 50 and 200 Hz. For that calculations, field-circuit and analytical methods are used, taking into account the nonlinear phenomena. The results show a significant increase in magnetizing current for two-pole motor concomitant with the use of nonmagnetic shaft. Calculated results have been verified by measurements.

PurposeThe large size of models and long computing time prevent the creation of full‐scale, three‐dimensional models of end region of turbogenerators. Only exact three‐dimensional model can illustrate complex phenomena of end region losses. Also some methods of decreasing such losses cannot be simulated in two‐dimensional models. The purpose of this paper is to focus on a method of creating three‐dimensional models of turbogenerators' end regions for calculations of eddy current losses.Design/methodology/approachTime‐stepping is the most expensive part of computation. A harmonic model would be free from that disadvantage and it can provide a tool to make an accurate, fully three‐dimensional model of a steady state for different loads and provide results in a reasonable time.FindingsThe research focuses on the method of creating three‐dimensional models of turbogenerators end region for calculations of eddy current losses. By using two‐dimensional, time‐stepping models and empirical loss functions for a main flux and three‐dimensional models for eddy current losses from a perpendicular flux of an end connections, it is found that fast analysis of that complex part of a machine can be achieved.Originality/valueThe approach proposed in the paper is a universal and novel method of calculation losses of turbogenerators' end regions. Combining two‐dimensional and three‐dimensional models provides advantages of both known methods: fast computation time from simplified models and good representation of complex geometry of a machine.

This paper presents a no-load core loss analysis of a three-phase energy-saving small-size induction motor supplied by a sinusoidal voltage. In the field-circuit approach, the distribution and changes of magnetic flux density in the motor are computed using a time-stepping finite-element method. The discrete Fourier transform is used to analyze the magnetic flux density waveforms in each element of the motor model. The rotational aspect of the field is included by introducing a correction to the losses generated by the first harmonic of magnetic flux density. The core losses in each element are evaluated using a loss curve measured on a toroidal core at different frequencies. Finally, an approximate analytical formulation is derived for rapid field computation. The results are compared with measurements.

PurposeThe purpose of this paper is to present a comparative analysis concerning the influence of eddy currents on the distribution of the magnetic flux density in the laminated anisotropic structures.Design/methodology/approachThe influence of the magnetic flux normal to the lamination surface is particularly analysed. Several models containing internal air gaps and overlapping are tested. For every structure, the eddy currents are first taken into account and then, they are neglected. At last, the 3D simulation of the anisotropic conductivity permits to analyse separately the longitudinal and normal flux in the structure and the eddy currents induced by those fluxes.FindingsThe study leads to a more realistic numerical model with conducting laminations. The results show that the normal flux does not turn at once on lamination. The normal and longitudinal fluxes induce eddy currents which modify the flux distribution in the laminated structure.Practical implicationsThe results of the presented simulations make it possible to elaborate a more realistic numerical model of homogenized characteristics taking into account eddy currents.Originality/valueThe eddy currents induced by the fluxes modifies the field distribution in the structure and should be taken into account. The internal air‐gaps higher than 0.1 mm have an influence on the field distribution; the isolation between the laminations of 0.01 mm has a smaller but not negligible effect on the magnetic flux. The direction of the normal flux from one sheet to another one does not change immediately after the entrance of the lamination, the transition is progressive.

PurposeThe purpose of this paper is to present the plan to develop the known algorithm for thermal and electromagnetic coupled problem calculation. This is used for three‐phase induction motor (IM) on nominal load. An additional purpose is verification empiric expressions of the heat transfer and equivalent thermal conductivity coefficients for external faces and air zones in analysed motor taken from literature.Design/methodology/approachThe numerical investigations proposed in this paper are based on 3D finite element models for thermal and electromagnetic fields analysis. Electromagnetic analysis includes iron core losses. It gives additional heat sources to thermal analysis. Heat transfer and equivalent thermal conductivity coefficients are assessed applying empiric expressions. Thermal model is experimentally validated.FindingsThe results of calculations and experimental test shows that heat transfer coefficient for external zones taken from literature does not guarantee the equal accuracy of the distribution of the temperature in all volume of the machine.Research limitations/implicationsTaken from literature, empirical equations do not give correct values of heat transfer coefficient. It states ways to go further in the evaluation of heat transfer coefficients.Originality/valueThis paper presents modelling methodology of 3D transient thermal field coupled with electromagnetic field applied in three‐phase IM at rated load conditions.

Purpose – This paper aims to present the plan to develop the known algorithm for thermal and electromagnetic coupled problem calculation. This is used for a one‐phase induction motor with locked rotor for nominal and lowered voltage excitation values. It also aims to prepare a calculating method for the average heat transfer coefficient for natural convection from the induction motor housing external face.Design/methodology/approach – The numerical investigations proposed are based on 3D finite element models for thermal and electromagnetic fields analysis and 3D volume element model for average heat transfer coefficient calculations. The thermal model is experimentally validated.Findings – The paper provides a numerical method to calculate average heat transfer coefficient for the induction motor housing external faces. This coefficient is shown as a temperature function. Temperature variations in the various parts of the induction motor with locked rotor are calculated. The calculation results are compa...

PurposeThis paper aims to focus on the numerical modelling of 3D structure of surface micromachined (MEMS) accelerometers.Design/methodology/approachThe paper focuses on the methods of mechanical design and analysis of electrostatic accelerometers (comb drive structure) and uses computer simulation procedure leading to final structure design, then to be defined as a basic structure for stress analysis.FindingsThe strategy in computer modeling of accelerometer MEMS is satisfactory in order to simulate the electromechanical characteristics of different accelerometer structures (IMEMS).Originality/valueA novel complex strategy in computer modeling of accelerometer MEMS, based on solid modeling is proposed.

PurposeTo investigate the use of amorphous iron as the stator core material to increase the efficiency of electric machines in serialised production.Design/methodology/approachIn the design process of a new structure for the induction motor with a stator core made from amorphous iron it is necessary to apply the circuit method and the field‐circuit method. The use of the circuit method allows quick calculations of many versions of the designed motor, but the use of the field‐circuit method is necessary for verification of the maximal value of the flux density in the entire area of the cross‐sections of the motor core.FindingsA new construction for the small induction motor with the stator core made from amorphous iron was designed based on the classical structure of the four‐pole induction motor. In the designed motor a decrease of the electric energy costs was observed, which is much bigger than the material costs, and in effect lower total costs for the designed motor were obtained.Practical implicationsAccording to necessary changes in the motor construction, due to lower saturation limit for this material, the authors obtained a significant increase in the motor efficiency and a decrease in the total cost of the motor. The development of a new technology allows the cutting of amorphous magnetic materials and the production of electric motors from them.Originality/valueThis paper shows the possibility of using amorphous magnetic materials for stator core of small induction machines and the advantages of such construction for obtaining more efficient motor construction.

Applies the field/circuit two‐dimensional method and improved circuit method to engineering designs of the induction motor with stator cores made of amorphous iron. Exploiting of these methods makes possible computation of many different specific parameters and working curves in steady states for the “high efficiency” three‐phase small induction motor. Compares the results of this calculation with the results obtained for the classical induction motor with identical geometric structure.

This paper presents operational characteristics of a small induction motor with the stator core made of amorphous laminations, supplied from mains or a frequency inverter at 50, 100, and 200 Hz. Calculations were performed using field-circuit and equivalent circuit approaches, taking account of nonlinearity and additional losses, both in the core and in the windings. Data for mechanical losses, magnetization curves, and magnetic losses of the amorphous material were experimentally obtained; magnetic measurements were taken as a function of magnetic flux density in the frequency range up to 2000 Hz. Calculated results are compared with measurements.

This paper deals with the field and force calculation in a model electromagnet which is the power drive of the shuttle loom. Hermitian hierarchical finite elements have been successfully applied to the field and force computation of the electromagnet. The computational results have been reported.

Comparative calculations of electromagnetic field distributions in double salient switched reluctance motor based on the Finite Element Method (FEM) and the Reluctance Network Method (RNM) are presented. It has been shown that the results of calculations and measurements are in good agreement. The RNM can be successfully applied to torque calculations, while a simple discretization of the motor cross-section is used.

The complex geometrical structures, transient states and non‐linearity of the magnetic circuit of electromechanical converters are rather unfavorable for field calculation. A very small air gap width and different slot numbers of primary and secondary part of a converter cause big changes of the field gradients and thus demand a very fine discretization or even coupling different methods and formulations. Furthermore, these also cause scientists to look for the other more effective methods. In spite of these permanently growing possibilities of the software packages there still exists the need to look for more accurate methods for calculating the electromagnetic field in electromagnetic devices. In the paper, attention is focused on the transient states occuring in the power transformer. The solution of such a problem could allow engineers to estimate the power losses in tank walls and hot‐spots localization as well.