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Reducing losses in electrical devices is essential for reducing global energy consumption. Losses in the core of electrical machines constitute a significant part of the overall losses—their share increases with the number of machines powered by PWM converters, especially for high-speed machines. Limiting core losses requires precise determination at the design stage of the device. Achieving this goal is possible thanks to numerical or analytical simulation. A necessary input for this process is the correct determination of the properties of the core material. The sheet loss, however, changes due to the machining process, primarily punching. The subject of the work is to develop a sufficiently accurate approximation of electrical steel sheet-specific loss, taking into account the effects of cutting and the width of a given machine element for a wide range of induction and frequency. The method also enables the extrapolation of losses for higher frequencies relevant from the point of view of generating losses in the machine. The developed loss approximation can be used in the finite element simulation and in applying analytical methods. The technique can be successfully used for many grades of non-oriented sheet metal, provided that the requirements specified in the work are met. The proposed approximation allows us to determine the loss of a sample of a certain width in a wide range of magnetic induction magnitude and frequency with an accuracy not worse than 4%.

The paper proposes a simple structure of high-power solid-state transformers (SSTs) able to control the energy flow in critical lines of the medium-voltage (20 kV) distribution grid. With an increasing number of renewable intermittent sources connected at the nodes of the meshed distribution grid and a reduced number of nodes connected to large power plants, the distribution grid stability is more and more difficult to achieve. Control of the energy flow in critical lines can improve the stability of the distribution grid. This control can be provided by the proposed high-power SSTs operating a 20 kV with powers over 10 MW. This function is difficult to achieve with standard SST technologies that operate at high frequencies. These devices are made with expensive magnetic materials (amorphous or nanocrystalline cores) and a limited power by SST cells. The required total power is reached by assembling many SST cells. On the other hand, existing SST designs are mainly aimed at reducing the equipment’s size and it is difficult to design small objects able to operate at high voltages. The authors propose to use cores made with grain-oriented electrical steel (GOES) thin strips assembled in wound cores. Experimental results obtained, with GOES wound cores, show that the core losses are lower for a square voltage than for a sine one. This counterintuitive result is explained with an analytical calculus of eddy currents and confirmed by a non-linear time-stepping simulation. Therefore, simple converter structures, operating with rectangular voltages and low switching losses, are the best solutions. Experimental results also show that the core losses decrease with temperature. Consequently, high-power SST cells can be made with transformers whose GOES cores are hotter than coils for reducing core losses and keeping copper losses at low levels. The paper proposes an appropriate transformer mechanical structure that avoids any contact between the hot GOES wound core and the winding, with a specific cooling system and thermal insulation of the hot GOES wound core. The proposed design makes it possible to build SST cells over 1MW and full SSTs over 10 MW at moderate costs.

The global drive to reduce energy consumption poses new challenges for designers of electrical machines. Losses in the core are a significant part of losses, especially for machines operating at an increased rotational speed powered by PWM inverters. One of the important problems when calculating core losses is considering the effect of material degradation due to mechanical or laser cutting. To this aim, this paper analyzes and summarizes the knowledge about the sources of material property deterioration and ways of describing this phenomenon. The cited results of material tests indicate the lack of unequivocal relationships allowing us to estimate the degree of material damage and the resulting deterioration of material properties. The main task of this article is to present the state of knowledge on the possibility of taking into account the impact of cutting the core sheets of electric motors on core losses and their impact on the efficiency of the machine. This is a significant problem due to the need to design and manufacture energy-saving electric motors powered with a voltage of 20 to 350 Hz, whose magnetic cores are made of laminates. However, the performed analysis indicates the most important parameters of the cutting process, affecting the degree of material structure destruction. The method of the solution proposed by the authors for core punching and laser cutting, illustrated with a practical example, is also presented.

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.

Reducing induction motor losses is very important because of the fulfilment of increasingly stringent requirements set by international regulations for reducing electricity consumption. Since core losses begin to dominate in motors operating at higher frequencies the exact calculation becomes more and more important. The common view is that losses due to higher harmonics caused by stator and rotor slotting constitute an important part of losses in the motor core. Proper calculation of the core losses requires inclusion both hysteresis and eddy current phenomena. For the hysteresis simulation, method included in package Opera 3D has been used. Using that model it was possible to investigate flux behavior at high frequency like as for higher harmonics field. Next part is focused on practical determining of proper method for higher harmonics losses limitation.

This paper aims to present and analyze the materials adapted to design a machine that can work with a high current density without any specific cooling system. In other words, the machine is equipped with material that supports high internal temperature, about 500°C. Candidate materials are selected and the authors indicate that inorganic insulation should be preferred for conductors and slot insulations. Tests are carried out on material selection through measurement of the turn-to-turn voltage, insulation resistances, and the parallel capacitances.

The article proposes an analysis of the possible architectures of synchronous machines with an ability to operate at high temperatures of over 200°C in their environment. Two machine principles have been considered: the permanent magnet synchronous machine and the synchronous reluctance machine. The numerical analyses are carried out with 3D-coupled electromagnetic-fluid-thermal models; the electromagnetic one provides the local losses that give the input data to the coupled thermal-fluid analysis model for computing the temperatures inside the machines. The simulation results are used for estimating the temperature limit of each machine architecture, considering the characteristics of their critical parts.

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.

Purpose The purpose of this paper is to present the application of the loss approximation method for non-oriented electrical steel developed by the authors. A new model of a toroidal sample with dimensions ensuring high uniformity of the field was presented. Design/methodology/approach A critical analysis of the methods used was carried out. Based on these considerations, the authors proposed their own loss approximation method, which allows obtaining high accuracy in a wide range of induction and frequency. The proposed method is based on the assumption that for a certain frequency range losses can be describe by two terms formula. For a fixed value of the peak flux density Bm, the graph of specific loss divided by the frequency should have the form of a straight line. Then, the obtained coefficients for different Bm are the basis for approximation with the power function. Findings The comparison of measurement and approximation results shows that the method allows to obtain very good accuracy in a wide range of induction and frequency. Research limitations/implications More detailed studies on the impact of cutting on a larger number of samples with different geometrical dimensions are needed. Practical implications Application of the new method provides a better approximation of the curve of the loss and thus a more accurate calculation of the core loss in the electrical machines. Originality/value The paper presents the application of the loss approximation method for non-oriented electrical steel developed by the authors. A new model of a toroidal sample with dimensions ensuring high uniformity of the field was presented. It is shown that the approximation introduced allows for high accuracy in a wide range of frequency and magnetic flux density.

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.

In this study, the authors aimed to analyse the influence of massive ferromagnetic shaft on the distribution of the electromagnetic field and to evaluate the magnetising current from the mains. To achieve this, they used motors powered by 50 and 200 Hz. They also used both numerical two-dimensional (2D) and 3D field-circuit methods as well as an analytical method based on the results of field analysis. This modified analytical method is based on the magnetisation characteristics of the shaft's material. According to the results, there was a significant impact of shaft's saturation on the machine with one pair of poles in the form of a significant increase in the amplitude of induction in the rotor yoke, which resulted in an increase in the magnetising component of the current drawn by the motor from the grid. This phenomenon was found to increase, in particular, when using non-magnetic shafts. In the case of machines with two pairs of poles, this effect was found to be much smaller than that of one pair of poles. They verified the results experimentally by comparing the calculated and measured magnetising currents.