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.
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%.
In the drives of high-speed devices, such as a blood centrifuge, dynamic states also play an important role in terms of the time and quality of the tests performed. The article presents the application of modified equations resulting from the mathematical model of an induction motor to model dynamic phenomena during motor start-up, both with mains supply and with frequency start-up. The applied solution considers the phenomenon of current displacement in the rotor bar and the phenomenon of saturation. The comparison of the obtained results with the experiment shows that the method is sufficiently accurate. The obtained results can also be extended to higher power machines and to modeling other dynamic states.
The process of cutting laminations from which the cores of electric machines are built causes a change in their magnetic properties and losses, which can significantly affect machines’ parameters, mainly losses of power and efficiency. Electric motors are a significant consumer of electricity; therefore, the problem of increasing their efficiency is fundamental from the point of view of environmental impact. The subject of the work is the study of the influence of punching and laser cutting on the magnetization and loss characteristics of sheets, taking into account the phenomenon of magnetic anisotropy. For this purpose, samples cut in different directions were tested. As the direction of the field action in the motor core varies in different parts of the machine and time moments, it was investigated how to obtain average characteristics for different directions of magnetization. Then, a simplified method for determining the characteristics of punched sheets of various widths based on small-width samples and water cut samples is presented. The proposed solutions allow for refinement of the calculations of magnetic circuits with a simplified consideration of the influence of punching.
The classic relationships concerning the harmonic content in the air gap field of three-phase machines are presented in form of series of rotating waves. The same approach is applied to modeling of permanent magnet motors with fractional phase windings. All main reasons of non-sinusoidal shape of flux density distribution, namely, magnets’ shape and their placement, slotting, magnetic saturation and eccentricity are also related to their counterparts in modal-frequency spectrum. The Fourier 2D spectrum of time-stepping finite element solution is confronted with results of measurements, with special attention paid to accuracy of both methods
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