94 publications from this institution
This paper deals with a new kind of superconducting limiter. Usually, superconducting current limiters are based on the transition from superconducting state to the normal state by overtaking the critical current. This new superconducting current limiter has no current transport in the superconductor. Indeed, in our structure, the limitation is based on the saturation of a high temperature bulk superconductor by the magnetic flux. We show that our structure enables one to limit the current.
The application of geotechnical centrifuge modeling to environmental problems seems promising. In this paper, one aspect of similitude laws concerning the flow of water through soils is investigated. Within the Network of European Centrifuges for Environmental Geotechnic Research, several tests have been carried out to study similitude laws describing the capillary ascension in porous media at different levels of acceleration. The aim of this paper is to present the results obtained at Ruhr-Universität Bochum. A fine sand is used in the experiment. For the visualization of capillary height in the soil sample, image processing is used. Different boundary conditions (constant or variable water level) have been investigated and discussed. All these experiments confirm that capillary rise appears scaled by the factor N and time seems to be scaled with N2. Thus, these results support the possibility of extending the use of accelerated small-scale models to the capillary phenomenon in centrifuge and open the way to more complex investigations of flow and pollutant transport in unsaturated soils.
Abstract This work presents a model of a three‐phase induction machine which includes the first space harmonics of the magnetomotive force. Special attention has been paid to the way of improving detection of broken rotor bars. This detection is based on the spectral analysis of the stator current. We show that it is essential to extend the analysis to the amplitudes of the side bands due to the space harmonics. This thorough method makes it possible to detect with a higher degree of accuracy the type and the importance of a defect in the rotor cage. Copyright © 2005 John Wiley & Sons, Ltd.
Vector controlled induction machine drives are increasingly used in industrial drive systems, but the drive performance often degrades with the machine parameter variations. In this paper, a modified vector control system is proposed to achieve decoupling when saturation and iron losses are taking into account. The simulated and experimental results of the modified controller are presented to verify the effectiveness of the proposed approach.
This paper deals with an implementation of a stator flux oriented method on a DSP board to drive an induction motor. This method is based on the integration of EMF directly provided by two extra coils located on the equivalent /spl alpha/, /spl beta/ reference axes of the stator. The open-loop integration problem is solved thanks to an online offset compensation algorithm which offers robustness especially at low speed. Experimental results of speed control are presented and commented to show the effectiveness of this method.
The influence of the startup instant of the quench in a superconducting current limiter is studied. The heat transfer equation is numerically solved, using the finite difference method, and taking the effects of current sharing into account. The results show the importance of this instant on the dissipated power, the temperature-increase and on the efficiency of the current limitation.
The analytical modeling of toric coils is considered. The mathematical relations involve elliptic integrals which are rapidly and easily calculated using the arithmetic geometric mean (AGM) method. Two applications are studied, numerical results are analyzed and compared, when possible, with those obtained directly. The analytical method presented provides all the characteristics (such as inductances, flux densities, forces, etc.) of toric coils with any section. Thanks to the AGM method, which is used for intermediate calculations, the final results are obtained rapidly with a very good precision.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
This paper presents an efficient tool for design analysis of a Synchronous Reluctance Motor (SynRM).The Winding Function Analysis (WFA) is used instead of the Finite Element Analysis (FEA).With WFA approach, parameters sensitivity analysis and the impact on the machine design can be evaluated very rapidly (under linear condition).The effect of rotor skewing, stator winding chording, pole arc and interpolar air-gap length on average torque and torque ripple is investigated.The results obtained by WFA are compared with those obtained by two-dimensional FEA.It is shown that the two methods give approximately the same results but require different computation time.
