A. Foggia

Simulation of induction machine operation using a step by step finite element method coupled with circuits and mechanical equations

The authors present the modeling of an induction machine using a nonlinear magnetodynamic complex method coupled with the circuit equations. The method is an extension to the harmonic solution of nonlinear magnetodynamic problems of the proposed classical finite element method. The coupling of the circuit equation completes the 2-D finite element method by making it possible to take into account the 3-D part of the motor. Another advantage is the ability to include voltage sources. >

End winding reactance computation using a 3D finite element program

The computation of end winding reactance using a 3-D finite element program is presented. The program used is FLUX3D, which takes into account the exact geometry of the machine and the 3-D distribution of the flux density. Special attention is focused on induction machines. Different windings are analyzed and, when available, experimental results are compared against computed values. The comparison shows very good agreement between the two values. >

Finite Element Modelling of a Synchronous Machine : Electromagnetic Forces and Mode Shapes

Manufacturers in electrical machinery are becoming highly interested in the reduction of noise and vibrations; this is due to the increasing awareness of the problem in some industrial and military applications : one of the main causes of noise production in electrical machines is resonance between the electromagnetic force and the stator. Two fundamental steps are of importance to deal with the acoustic noise reduction problem: -study and assessment of the vibration behaviour of the stator (resonant frequencies, mode shapes....); -analysis of the electromagnetic force distribution. The objective of this paper is to report an advancement of the above works using the finite element method. The results of all previous steps are mentionned and discussed below. For this work we have used a permanent magnet synchronous machine.

Analysis of shaft voltages in large synchronous generators

In order to improve maintenance of large turbogenerators, a new diagnostic tool is developed by analysing shaft voltages. This study is validated by a comparison between the measurements made on a 30 kVA synchronous machine and its modelling with a finite element program.

Circulating current analysis in the parallel-connected windings of synchronous generators under abnormal operating conditions

In large synchronous generators, the windings are usually parallel-connected in order to deliver the normal characteristics at the terminals of the machines. Under normal conditions, there is no circulating current between the windings of one phase. But when a failure occurs like an eccentricity or some other faults, the symmetry between parallel windings is broken and a circulating current will occur. The aim of this paper is to compute the current that circulates under faulty conditions like eccentricity and short-circuits in the rotor winding. A comparison with measurements made in a laboratory machine is also presented.

3D finite element computation of the high frequency parameters of power transformer windings

A computation of power transformer parameters with a numerical method using finite elements is presented. The modeling, based on the calculation of the 3-D electromagnetic field, allows a novel approach to the study of the high-frequency phenomena that propagate along the transformer windings. These parameters include the inductive and capacitive parts of a discretized winding. The energy method is used for finding the inductive parameters. The capacitive matrix is obtained using a method based on the computation of the charge on each disk winding. These methods are very efficient compared with analytical and 2-D numerical techniques: they allow the exact computation of the discretized winding parameters for any complex 3-D geometry. Examples of calculated parameters are given. An objective is to establish a computational model to study the propagation of step front surges along transformer windings. >

Magnetic fields in nonlinear anisotropic grain-oriented iron-sheet

The authors propose a 2-D magnetic field calculation method that takes into account the nonlinear anisotropic property in the grain-oriented steel. An elliptical model is used; the magnetic permeability is represented by a tensor with field-dependent components. This model is applied to a finite-element method using a scalar potential. The iron nonlinearity is considered and a Newton-Raphson method is applied to a family of B-H curves to improve convergence. To minimize variation of flux density between elements, an auto-adaptive process has been used. This modelling of nonlinear anisotropic magnetic fields is applied to a three-phase transformer core. >

Some armature reaction compensation methods numerical design of experiments and optimization for a hybrid excitation machine

This paper presents a hybrid excitation synchronous machine which combines a permanent magnet excitation with a wound field one. With two sources of flux, this kind of machines is cited more and more frequently in vehicle application for easier control of flux. After a brief description of the structure, some methods will be presented to improve the performances of this machine. Simulation results have shown that the armature reaction has a magnetizing effect when it enters in a pole face and a demagnetizing effect when getting out from the same pole, which distorts the main field and to some extent deteriorates the performances of the machines. The methods we present here are based on the principle of armature reaction compensation which might be extended to many synchronous machines. And then, in the last section, a general optimization tool (numerical design of experiments and optimization) is used to maximize the impacts of these methods.

Magnetic discretion of naval propulsion machines

Magnetic silencing is required for specific naval applications, especially for some oceanographic or military ships. It is therefore necessary to study the field radiated by electrical propulsion motors. This can be achieved using a numerical modeling based on magnetic moments. In the present paper, this model is presented and then compared to some experimental signatures for validation.

A three dimensional finite element analysis of the magnetic field in the end region of a synchronous generator

The magnetic field in the end-winding region of a synchronous generator is intrinsically three-dimensional. The aim of this paper is to show the contribution of 3-D finite element field-computation software in the analysis and the understanding of the magnetic field distribution in these regions under steady-state conditions.