INVESTIGATION OF THE CROSS-MAGNETIZING PHENOMENON IN SATURATED SYNCHRONOUS MACHINES APPLYING THE FINITE ELEMENT METHOD
Date
2003-09
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Masters
Abstract
It has been recognized recently that the magnetic coupling between the direct and quadrature axes of saturated synchronous machines(the cross-magnetizing phenomenon) plays an important role in their analysis. This phenomenon results in the reduction in the magnitudes of the direct- and quadrature-axis magnetic fluxes from their corresponding magnitudes. The fundamental components of the induced electromotive forces corresponding to these reductions in the magnetic fluxes could be used as the parameters representing the cross-magnetizing phenomenon. To calculate these parameters, the two-dimensional finite element method is applied to determine the parameters from the static electromagnetic field solutions. A specially designed synchronous machine that can be excited from both its direct and quadrature axes is used in the investigations in order that the parameters representing the cross-magnetizing effect could be measured experimentally and, thus, the accuracy of the solutions using the finite element method can be verified.
In order to obtain these parameters, the saturation characteristics of the machine in the direct, quadrature and various intermediate axes are needed. The calculations of these characteristics using the finite element method are carried out on both the central line of the air gap and the inner surface of the stator of synchronous machines for three different relative positions between the stator and rotor. Four models with different air-gap lengths have been considered in the investigations. These calculations indicate that their accuracy are not practically affected by performing the calculation on the central line of the air gap or on the inner surface of the stator and, thus, both cases can be used without affecting the accuracy. With regards to the relative positions between the stator and rotor, there are only very slight discrepancies between the calculated results for the various relative positions considered and practically the relative positions have no effect on the accuracy of the calculations. Thus, the calculations can be carried out at any relative positions. Moreover, the knowledge of the accurate values of the air-gap length
11of the synchronous machines is essential to obtain accurate results for the saturation characteristics of the synchronous machines. Since such accurate values are usually not available, the d-axis saturation characteristics calculated by the finite element method can be used to obtain accurate estimations of the air-gap length by fitting these calculated results with the measurable d-axis open-circuit characteristics. The accuracy of the calculation of the saturation characteristics has been verified by comparing them with the measured open-circuit characteristics of the specially designed synchronous machine.
With regards to the cross-magnetizing phenomenon, the results of the investigations carried out in the thesis have confirmed its existence and have shown that the calculated parameters representing this phenomenon using the finite element method are in a
reasonable agreement with the measured values. This lends credence to the use of the finite element method for predicting these parameters.
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Degree
Master of Science (M.Sc.)
Department
Electrical Engineering