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The torque harmonics generated by asynchronous machine slotting are essentially linked to air‐gap permeance variations due to the rotor rotation. These variations lead to machine inductance coefficient fluctuations which are at the begining of torque harmonics. So the problem consists to determine the permeance variation law as well as for its mean value that for its “harmonics”. The aim of this study is to end at analytical expressions which allow to calculate the torque harmonic magnitudes whatever the considered machine. In consequence the numerical methods (e.g. finite element method) are not appropriated because their implementation considering the rotation will be too long and, in the other hand, they only permit, from calculus results, to estimate this permeance variation law. To resolve this problem by analytical way this law must be characterized by a simple expression. That leads the authors to translate the complex phenomena, linked to the field line repartition in the slotting, by simple laws applied to a fictitious slot model. After presenting the selected model to characterize the slots, the authors introduce the angle per unit permeance notion which permits to make clear the air gap permeance variation law in function of rotor rotation. The experimental verifications which relate to inductance coefficients and torque harmonics permit to validate these permeance variation law and in consequence the selected fictitious slot model. The evolution of these quantities in function of the magnetic field magnitude inside the machine permits the authors to propose a fictitious slot model evolution law which can take the saturation into account.

The aim of this paper is to estimate the iron losses for an induction machine in the healthy case taking the slotting effect into account and to study the effect of an inter‐turn short‐circuit on these losses. Theoretical results are then compared with experimental ones.

A simple analytical model of iron losses allows one to calculate and to appreciate the contribution of the slotting effect on induction machine iron losses without and with an inter‐turn stator short‐circuit. This semi‐analytical approach is based on the iron stator and rotor flux density repartition which is deduced from the air‐gap flux density.

The iron losses are not only due to the fundamental air‐gap flux density, but also to the slotting harmonics. In fact, the slotting effect generates harmonic flux density waves with very low magnitudes but with high‐angular velocities, leading to non‐negligible harmonic iron dynamic losses which have similar values on both the stator and the rotor. The inter‐turn short‐circuit generates an iron losses and a slotting harmonic contribution increase.

Experimental measurements give the total iron losses. They do not allow separating the fundamental and the slotting harmonics contribution.

The knowledge of the iron losses behaviour in the healthy machine taking into account the slotting effect is important to optimize the design. The fault contribution on these losses allows one to estimate the damage which can be engendered by the fault.

Generally, iron losses studies and calculations are performed numerically using finite element software. The analytical approach can be interesting because it allows one to make faster calculations and to analyze the influence of the machine geometric parameters.

Electrical machines are more and more fed by static converters. These power supplies impose nonsinusoidal statoric waveform to the machines. In these conditions, behaviour of magnetic material can be very different compared with sinusoidal ones. The characterization of magnetic material under non‐sinusoidal excitations is not clearly defined. At the present time, there is not any standard about operating test and specific parameters to be measured in order to get efficient knowledge of soft magnetic materials in distorted excitation mode. The aim of this paper is to present the effect of statoric connections on harmonic characterization parameters. The experimental results correspond to a Fe‐Si non oriented material excited by two different waveforms in a classical Epstein frame. The behaviour of the material is divided into two parts: the fundamental and the harmonic responses. The fundamental parameters are representative of the duty frequency of the machine, harmonic ones give information about additional losses; especially their harmonic distribution. They also allow us to estimate harmonic impact on the fundamental response.

The 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).

An 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.

The 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.

The 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.

The method offers an automated process to reduce considerably the component of highest amplitude in the vibration spectrum.

For the proposed coupling transformer, a magnetic bypass based on the virtual air gap principle is realized by inserting auxiliary windings in a return leg added to a standard transformer. With such a setup, it is able to act as a voltage regulator as well as protect the power electronics of the dynamic voltage restorer from electrical grid fault currents. This paper focuses on the electrical design part of the coupling transformer. It aims to explain how the behavior of the auxiliary windings electrical circuit of the magnetic bypass impacts the performances of the device.

The influence of the electrical auxiliary windings circuit configurations on the operation of the coupling transformer is studied by finite element analyses with nonlinear and isotropic magnetic materials.

A configuration for the realization of the electrical circuit of the auxiliary windings is determined according to the finite element simulation results to achieve the design of the coupling transformer whose magnetic core was previously designed.

By studying the operation of a special coupling transformer with nonlinear saturation phenomenon by finite element analyses, a to-do list of the electrical circuit parameters is described to design this device well.

This paper aims to present the principle of virtual air gap inductance and the design of a voltage regulation device based on this principle. The authors provide a comprehensive analysis of this specific application that consists of locally saturating the magnetic circuit of the voltage regulator to modify its global properties. This saturation is created by a direct current flowing in a small auxiliary coil inserted in the specific area of the magnetic circuit to saturate this zone.

Analytical calculation and finite elements simulations are used to optimize the device for a specific application tied to the supply of electrical ovens in metallurgic usage. Experimental results are presented at the end of the paper.

The experimental results presented in this paper are in concordance with the analytical calculation and with the finite element simulations for different operation points. The difficulty of the study of the virtual air gap comes mainly from the nonlinearity of the phenomena because the principle is based on a local and controllable saturation of the magnetic circuit.

The originality of the paper concerns the introduction of virtual air gap principle in a specific industrial application.

Non‐intrusive magnetic measurements in AC machines are possible with small flat coils stuck on the external surface of the housing of a running motor. The aim of the paper consists in determining transmission coefficients able to give a direct relationship between the weak external flux density and the airgap one.

An experimental approach shows that the decoupling principle can be applied. Transmission coefficients are determined separately for the stator yoke, the motor housing and the external air.

For low frequencies and a housing made of steel, eddy current can be neglected. The transmission coefficient depends strongly of the mode (number of poles) of the rotating field. Conversely, for higher harmonic ranks, the additional attenuation caused by eddy currents in the housing does not practically depend on the mode but is strongly dependant on the frequency.

The transmission coefficients are determined considering a 2D electromagnetic model and several simplifying hypothesis. Experiments prove the validity of the proposed approach up to 550 Hz.

Up to now, many fault detection systems are based on the presence of additional harmonics in the external magnetic field spectrum. With the knowledge of simple transmission coefficients, an analysis of the variation of the magnitude of critical spectrum lines is now possible for a more precise fault detection in AC machines.

To the authors' knowledge, the only alternative way for the interpretation of external field measurements consist in using a numerical method with a full model of the machine which takes a lot of computation time. The proposed transmission coefficients provide a faster method valid for most of the interesting spectrum lines.

This paper aims to study the influence of supply voltage variations on the external magnetic field emitted by grid-powered induction machines (IMs).

Two models are developed in the paper to analyse, for different supply voltage values, the influence of the variations of the magnetizing voltage for which there is a link with the tangential component of the external flux. The first is an analytical model based on the IM single-phase-equivalent circuit with variable magnetizing reactance to take into account the saturation of the magnetic circuit. The second is a numerical finite element simulation to model the same phenomenon. Results of both models are analysed with experimental measures of the external flux.

The study shows that the amplitude of the external field strongly depends on supply voltage values.

The investigation is mainly focused on the tangential component of the external magnetic field which is of high importance concerning the applicability of non-invasive methods of diagnosis, as electromagnetic torque estimation developed by the authors or internal fault determination.

The originality of the paper concerns the characterization of the external flux with the supply voltage for IMs. It is shown that the magnetic circuit radiates external flux differently with the load and with the supply voltage.

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.

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.

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.

In future research authors will take into account motors feed from PWM inverter, working in the frequency range up to 400 Hz.

The results of investigation will be used in more detailed design of IMs especially for motors with closed rotor slots.

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.

The purpose of this paper is to present a design method for induction machines including a three-phase damper winding for noise and vibrations reduction.

In the first part, the principle of the damper winding is recalled. The second part presents the iterative design method which is applied on a 4-kW pulse width modulation (PWM)-fed induction machine to study the impact of the additional winding on the geometry. In the third part, the finite-element method is used to validate the designed geometry and highlight the harmonic flux density reduction. Finally, some experimental results are given.

The study shows that the impact of the additional three-phase winding on the geometry and weight of the machine is low. Moreover, the proposed noise reduction method allows one to reduce the total noise level of a PWM-fed induction machine up to 8.5 dBA.

The originality of the paper concerns the design and characterization of a three-phase damper winding for a noiseless induction machine. The principle of this proposed noise reduction method is new and has been patented.