A degradation of metallurgical equipment is normal process depended on time. Some factors such as: operation process, friction, high temperature can accelerate the degradation process of metallurgical equipment. In this paper the authors analyzed three phase induction motors. These motors are common used in the metallurgy industry, for example in conveyor belt. The diagnostics of such motors is essential. An early detection of faults prevents financial loss and downtimes. The authors proposed a technique of fault diagnosis based on recognition of currents. The authors analyzed 4 states of three phase induction motor: healthy three phase induction motor, three phase induction motor with 1 faulty rotor bar, three phase induction motor with 2 faulty rotor bars, three phase induction motor with faulty ring of squirrel-cage. An analysis was carried out for original method of feature extraction called MSAF-RATIO15 (Method of Selection of Amplitudes of Frequencies -Ratio 15% of maximum of amplitude). A classification of feature vectors was performed by Bayes classifier, Linear Discriminant Analysis (LDA) and Nearest Neighbour classifier. The proposed technique of fault diagnosis can be used for protection of three phase induction motors and other rotating electrical machines. In the near future the authors will analyze other motors and faults. There is also idea to use thermal, acoustic, electrical, vibration signal together.

The authors describe experimental and theoretical analyses of faults of power transformer winding. Faults were caused by mechanical effect of short-circuit currents. Measurements of transformer were carried out in high-voltage laboratory. Frequency and time diagnostic methods (method SFRA - Sweep Frequency Response Analysis, impact test) were used for the analyses. Coils of transformer windings were diagnosed by means of the SFRA method and the time impact test. The analyzed methods had a significant sensitivity to a relatively small deformation of coil. In the analysis a new technique for analyzing the effects of short-circuit currents is introduced. This technique is developed for high-voltage transformers (different types of power). The proposed analyses show that it is necessary to analyze the value of short-circuit current. Short-circuit current represents a danger for the operation of the power transformer. The proposed approach can be used for other types of transformers. Moreover, the presented techniques have a potential application for fault diagnosis of electrical equipment such as: transformers and electrical machines.

The paper presents an analysis of test results by Frequency Domain Spectroscopy (FDS) of the loss tangent (tgd) in electrotechnical pressboard impregnated with insulating oil and containing nanoparticles of water depending on the frequency of alternating current, sample temperature and degree of moisture. We found tgd reduction in areas of low and ultra-low frequency. It is associated with relaxation due to the hopping conductivity (tunnelling) of electrons between moisture nanoparticles occurring in the cellulose impregnated with insulating oil. In frequency areas close to the local minimum of tgd and higher, relaxation does not depend on the moisture content and is associated with other polar molecules which are part of the cellulose. We developed a new method converting experimental frequency dependence of the loss angle tangent, measured by the FDS method to the reference temperature of 293 K (20°C), using the exponential dependence of the relaxation time on the temperature, was developed. The activation energy of the relaxation time was determined based on the loss angle tangent of moist electrotechnical pressboard impregnated with insulating oil. It was found that the variation in moisture content in the composite cellulose-mineral oil-water nanoparticles do not cause changes in the activation energy of the relaxation time. The conversion of experimental frequency dependence of the loss angle tangent determined by the FDS method to the reference temperature of 293 K (20°C) eliminates the temperature dependence in the areas of ultra-low and low frequencies occurring in the runs made directly on the basis of the measurement results. After calculating the frequency dependence of the loss angle tangent to the reference temperature, all that remains is its dependence on the moisture content.

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