Search results

Electrical machines with nonlinear magnetic circuits are usually modelled by coupling magnetic and electric equations using software for magnetic field investigation. These hybrid methods are practically effective only for steady states, due to their time‐consuming calculations. The separation of both sets of equations will be possible if the unique relationships between linked fluxes and all armature currents become determined. It needs, of course, the neglect of the eddy‐currents in the machine rotor. Generally, they are defined as the partial derivatives of coenergy:

The aim of the paper is to present the approximation methods of the magnetizing characteristics of the salient pole synchronous machines with the fundamental MMF harmonics.

The energy based approach is used to formulate a set of the functions approximating the magnetic flux linkages versus an equivalent magnetizing current in the circuit model of the synchronous machine. The estimation of the approximation functions parameters is based on the results of the field calculations.

The identification of the approximation functions is effective and significantly simpler on the basis of the magnetic field co‐energy function, than on the basis of the magnetic flux linkages.

The magnetic field co‐energy function determined by FEM is sufficient for simplified calculations of the magnetic parameters occurring in the circuit models of the electrical machines with nonlinear core.

The paper provides guidance for the circuit modelling of the multi‐pole generators and motors under conditions of magnetic saturation.

A paper has succeeded in determining the internal magnetic characteristics of the synchronous machine with a salient pole rotor.

Non‐linear characteristics, as relations between linked fluxes and currents of individual machine coils, are sought for in the so called circuit models of saturated electrical machines. Their determination can be based on the co‐energy of the magnetic field only, which is a multivariable function of all coil currents and rotor position angle. The author proposes the calculation of co‐energy values at necessary points by the FEM and the interpolation of the results by a suitable multivariable spline function. The functions of linked fluxes are generated as the first derivatives of the spline. This way could be used to separate the circuit calculation from the field calculation when saturated machines are modelled. An example of a wound rotor induction machine is used to show the elementary problems of the calculation of the non‐linear characteristics.

The purpose of this paper is to present the differences in results of numerical calculations arising from different simplifications of the rotational magnetization model in typical dynamo sheets.

A comprehensive model of rotational magnetization processes in typical dynamo sheets should take into consideration the magnetic hysteresis and eddy current phenomena and also certain anisotropic properties. The chosen model of the rotational magnetization is briefly presented in this paper. A method of the inclusion of the rotational magnetization model into equations of the magnetic field distribution is described. The correctness of these equations has been verified experimentally. Numerical calculations of the rotational magnetization in two types of dynamo sheets were carried out for several simplifications of the described model.

Results of numerical calculations of the rotational magnetization with the omission of the hysteresis phenomenon or with the omission of eddy currents were compared with results obtained with the use of the comprehensive model of the rotational magnetization.

The paper presents comments and recommendations concerning the omission of both the hysteresis phenomenon and eddy currents in the analysis of the rotational magnetization in dynamo sheets and the impact of these simplifications on numerical calculation results.

The content of the paper refers to very important issues of modeling and calculations of the rotational magnetization in typical dynamo steel sheets.

To study effects in the Fourier spectra of cage motor phase currents due to saturation of the main magnetic circuit by the fundamental MMF harmonic.

An idea of an equivalent magnetizing current is applied, which allows to consider an influence of all currents of stator and rotor windings on the main magnetic circuit permeability. The energy base approach is used to write machine equations and the harmonic balance method is used to determine the Fourier spectra of currents.

It has been shown that the saturation generate additional harmonics in phase currents, which are shifted by 100 Hz from the so called slot harmonics.

A model and a solving method allows to predict all slot harmonics quantitatively, but qualitative difference of the Fourier spectra to measurement still exist.

More precise prediction of the Fourier spectra of stator phase currents for on‐line diagnostic systems.

A circuit model of a cage motor accounting for saturation by slot harmonics and an algorithm for determination of additional components in the phase current Fourier spectra.