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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.

PurposeThe purpose of this paper is to suggest a procedure which makes it possible to reduce the radial vibrations of doubly salient switched reluctance motors (SRMs).Design/methodology/approachAn analytical method for the SRM radial vibration determination is first described. It is then extended to the active vibration reduction. An auxiliary winding equips the stator. The paper explains how the corresponding currents have to be adjusted to achieve a simple and robust control, with a special emphasis about the compatibility of the main and auxiliary supplies and about the reduction control principle. At last, an example of drastic noise reduction is presented.FindingsThe proposed method makes possible to define the theoretical vibration spectrum of SRM and thus it gives the major components to be reduced. The feasibility of automating the principle of active reduction is shown. The process of active reduction shows that a vibration component can be diminished by over 90 percent.Research limitations/implicationsThe active reduction is applied for reducing one component of the vibration spectrum. Future developments will focus on the simultaneous reduction of several components of vibration spectrum.Originality/valueThe method offers an automated process to reduce considerably the component of highest amplitude in the vibration spectrum.

This paper investigates a back to back test simulation of an interior permanent magnet (IPM) synchronous machine with fractional slot concentrated windings (FSCW). The studied machine is designed to equip a floating vertical axis wind turbine. The principal characteristics and the structure of the machine are presented, as well as the back to back test principle. The parking brake mode is investigated to determine at which aerodynamic torque the system converters have to be started. The designed system and the simulations results, obtained with the Matlab-Simulink platform are described. Simulation results obtained with the proposed control are compared to those obtained with the equivalent single-phase diagram.

In this paper, in order to predict magnetic acoustic noise emitted by electrical machines, five methods used to determine machine natural frequencies are presented and compared considering elementary structures such as smooth cylinders. Then, the cases of toothed rings such as induction and switched reluctance machine stators are taken into account, leading finally to consider these complete machines. The different methods can be divided into three sets. The first one is analytical and considers Jordan laws and suggested extension. The second one uses a finite element software. The three other methods are experimental and make use of an impact hammer, a shaker and the magnetic excitation technique.

PurposeThis paper aims to propose a high‐frequency (HF) model able to compute the flux density in the vicinity of the laminated stator core of an AC machine.Design/methodology/approachExperiments form the main approach. Analytical results previously obtained with a simplified rectangular laminated structure are confirmed with a standard cylindrical magnetic core.FindingsThree frequency domains are defined, depending on the skin depth relative to the thickness of the magnetic sheets. A methodological approach is proposed for each domain. For higher frequencies, the magnetic core can be considered as transparent for external field computation.Research limitations/implicationsThe HF model is valid for skin depths much lower than the thickness of the magnetic sheets.Practical implicationsThe proposed HF model provides a link between the weak field measured in the natural void existing between the stator core and the housing of large electrical machines. With such a link, it is possible to develop a new monitoring system able to detect and to localize the partial discharges in the stator winding of a large machine.Originality/valueThe low‐frequency limit of the model has been measured. It corresponds to a ratio of 1/40 between the skin depth and the magnetic sheet thickness. Therefore this model offers a new perspective for maintenance applications.

The paper develops an efficient computational method for establishing equivalent characteristics of magnetic joints of transformer cores, with special emphasis on step-lap design. This enables comparative analysis of designs without the need for difficult measurements.

Vibration and acoustic noise can be particularly severe in the switched reluctance machine (SRM). The results of an analytical study for calculating the radial force and predicting the acoustic noise are described. Building on an airgap permeance model, analytical developments take into account the slotting effects to determine the flux density harmonics and then the pressure components using a Maxwell formula. Mechanical aspects are also developed with natural frequencies determined using extended Jordan laws. A series of step-by-step experimentations allow validation of the analytical theory. Theoretical inductance, flux in the airgap, vibration and noise spectra are successively compared to experimental ones. A new noise cancellation technique is then presented, based on current harmonic injection in auxiliary windings. The new reduction technique concerns an SRM with two short pitch windings, such as the structure of brushless doubly fed reluctance machine. Using this new method, experimental results show that the vibration and acoustic noise produced by the SRM can be reduced dramatically. It allows the reduction of any mode 2 component of the acoustic spectrum without significant consequences on the other ones and without affecting the performance of the drive. An experimental example of marked reduction is given.