Adam Warzecha

The paper deals with the main effects occurring in the phase currents of cage induction motor with rotor and stator core anisotropy. Searching for the currents spectrum components was conducted basing on the form of magnetic field energy function. The nonlinear function approximating main field energy versus magnetising flux linkage consist of all windings main flux linkages. The leakage fluxes of winding were omitted because the research has been limited to the motor free running only. The specified current frequency components were sought in the measurement current spectra of tested double-cage motor. The positive and negative symmetrical components of frequency components being multiplication of supplied frequency are produced by the stator core anisotropy. The frequency components dependent on rotor slip are generated by the rotor core anisotropy. Presented results may be useful in the diagnostic of induction motors.

Accurate fault diagnosis systems should consider both the historical performance and the assessment of the current state of a machine. Manufacturing, installation, operation and maintenance are part of the machine's history and should be taken into account. The paper focuses on experimental procedures to develop a multi-criteria methodology to classify up to ten machine conditions. Using machine learning for signal processing techniques, any deviation from a normal steady state might be categorized as an abnormal behavior and, when demonstrated, a fault. To take advantage of machine learning algorithms, a significant amount of data is needed. To demonstrate the procedure the authors examined a synchronous machine. The authors recorded currents and voltages primarily, in stator and rotor winding, well as rotational speed and electromechanical torque. The collected signals were filtered and pre-processed, and to 5038 features were calculated and transformed into a tidy dataset. The sparse Linear Discriminant Analysis algorithm was used to extract the most important defined features. The results are shown in 3D scatter plots; in which each machine condition is represented. It is then possible to visualize the ability of the model to identify the most discriminant features. The same method can be used for the diagnostic of other types of machine conditions.

Energy based approach was used in the study to formulate a set of functions approximating the magnetic flux linkages versus independent currents. The simplest power series that approximates field co-energy and linked fluxes for a two winding core of an induction machine are described by a set of common unknown coefficients. The authors tested three algorithms for the coefficient estimation using Weighted Least-Squared Method for two different positions of the coils. The comparison of the approximation accuracy was accomplished in the specified area of the currents. All proposed algorithms of the coefficient estimation have been found to be effective. The algorithm based solely on the magnetic field co-energy values is significantly simpler than the method based on the magnetic flux linkages estimation concept. The algorithm based on the field co-energy and linked fluxes seems to be the most suitable for determining simultaneously the coefficients of power series approximating linked fluxes and field co-energy.

Magnetic measurements, carried out by means of the Epstein frame, have shown that most typical dynamo steel sheets have certain anisotropic properties. In numerical analysis, anisotropic properties are taken into account with the use of the special function of the grain distribution in the given dynamo sheet. For engineering purposes, it is desirable to assess the influence of these properties on the changes of the magnetic flux density in typical dynamo steel sheets, especially during the rotational magnetization. For this purpose, measurements of the flux density changes and field strength changes in the circular-shaped samples of two selected typical dynamo sheets were performed. These measurements were carried out for several values of the current flowing in windings which generated the axial or rotational magnetic field in the test dynamo sheet. The influence of the magnetic anisotropy on the magnetization process was briefly discussed for both types of the magnetization processes

The Goss texture is a characteristic feature of grain-oriented transformer steel sheets. Generator sheets, which are produced as non-oriented steel sheets, should have isotropic features. However, measurement results of generator sheets, confirmed by crystallographic studies, indicate that these sheets are characterized by certain, quite significant anisotropy. The first purpose of this paper is to present the influence of textures of generator and transformer steel sheets on their magnetization characteristics. The second aim is to propose a method which takes into account the sheet textures in the calculations of magnetization curves. In calculations of magnetization processes in electrical steel sheets, models in which the plane of a sheet sample is divided into an assumed number of specified directions are used. To each direction a certain hysteresis loop, the so-called direction hysteresis, is assigned. The parameters of these direction hystereses depend, among other things, on the texture type in these steel sheets. This paper discusses the method which calculates the parameters of these direction hystereses taking into account the given sheet texture. The proposed method gives a possibility of determining the magnetization characteristics for any direction of the field intensity changes.

Purpose: 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.Design/methodology/approach: 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.Findings: 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.Research limitations/implications: 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.Practical implications: The paper provides guidance for the circuit modelling of the multi‐pole generators and motors under conditions of magnetic saturation.Originality/value: A paper has succeeded in determining the internal magnetic characteristics of the synchronous machine with a salient pole rotor.

Purpose – 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. Design/methodology/approach – 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. Findings – 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. Research limitations/implications – A model and a solving method allows to predict all slot harmonics quantitatively, but qualitative difference of the Fourier spectra to measurement still exist. Practical implications – More precise prediction of the Fourier spectra of stator phase currents for on-line diagnostic systems. Originality/value – 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.

In this paper, we present a concept of a diagnostic system, the so called ldquodistributed system for induction motors diagnosticsrdquo. developed at our university. A system, which will be installed in one of the Polish power plants. We propose a tele-diagnostics system (IDS) supporting diagnostic services (DS) located in a specialized diagnostic center (SDC). As for data transmission, the Internet and the Ethernet networks are used as inexpensive links, as it is more cost efficient to provide a remote the maintenance of the DS. In this context, a tele-measuring system (TMS) has been used and connected with a complex noninvasive diagnostic platform.