The purpose of this study was to validate a designed three phase power transformer with modern software that use finite element method, by analyze it from two points of view: magnetic and thermal. For that, on the analysis it will be used two modules from ANSYS software, ANSYS Maxwell 3D and ANSYS Mechanical, both coupled in the same environment, ANSYS Workbench. It has used the latest versions from ANSYS, Workbench 14.5 and Maxwell 3D 16. [1] On the same time, it can be seen the 3D magnetic nonlinear behavior of this three phase power transformer and thermal effects for the ferromagnetic core. Also it can be found the magnitude of B field, the regions with problems and the value of the total core losses for the same transformer but at 3 types of voltages: 330 kV, 400 kV and 430 kV.

Waveforms acquired from the excitation of the main generator from a power plant are analyzed with the Discrete Wavelet Transform (DWT). The proper Wavelet mother order and the proper decomposition tree were determined considering the energy deviations between subsequent decompositions and respectively the maximum approximation error generated by the signal re-composition process. Power quality indices were determined using DWT individually for all phases and globally, for the entire three-phase system. A comparative analysis considering the same indices (calculated using Fast Fourier Transform - FFT) was performed and small differences were noticed between corresponding indices. The conclusion is that DWT can be applied considering both steady regimes and respectively non-steady regimes for which the FFT is unusable.

The paper presents several theories related to definitions of powers and power factors in non-sinusoidal and non-symmetrical regimes. The theories must meet some requirements: (a) to facilitate the measuring of power quantities by using acquired electrical waveforms; (b) to support the correct quantification of powers and power factors for a fair charge; (c) to support solutions for efficient compensation of non-sinusoidal and non-symmetrical regimes, simultaneous with the power factor compensation along the fundamental harmonic. Only theories meeting the above-mentioned requirements are approached. Aspects specific to power definitions are discussed and commented. Three theories rely on the Fourier decomposition of non-sinusoidal waveforms, valid only for steady signals, whilst the fourth relies on the Discrete Wavelet Transform (DWT) and can also be applied to unsteady signals. Dedicated original data acquisition systems were used to acquire experimental data for three case studies. Data were analysed with original software tools, based on the Fast Fourier Transform and Discrete Wavelet Transform, implementing the approached theories. Comparisons between results yielded for analogue quantities proved that the approached theories satisfy the requirements for which they were created, except for the fourth theory, which can be used only for compensation purposes.

One presents a complex data acquisition structure used for the monitoring and diagnosis of a system used for electric power transmission in the zone of large power source. The structure is also used for the optimization of power network operation in order to use the network also for the transmission of electric signals other than those of 50 Hz. The schematic of the monitored system is presented, the test points are specified. The tests are performed with three independent synchronized data acquisition systems that can acquire up to 24 electrical quantities. The hardware and software solutions are described. Examples of using the presented solutions to record some electric quantities are provided. Real time information are obtained using the data acquisition structure along with the software packages dedicated to the data analysis and processing. At the end waveforms recorded in various points of the power group are provided.

Theoretical models, numerical simulations, and experimental tests for determining surges transferred between the windings of transformers subjected to lightning impulse are addressed. Considering the surges transmitted in the transformer windings have inductive and capacitive components, the proposed model is focused on five aspects: 1) voltage transmission by electromagnetic induction; 2) surge transferred in the transformer windings by capacitive coupling; 3) oscillating component of the voltage transferred between the windings; 4) voltage transferred between the primary and secondary windings; and 5) voltage transferred to the tertiary winding. The maximum transferred voltage is analytically determined. The simulation relies on the Math Script RT Module. Experimental tests were performed on two types of transformers. For the first one (type TTUS-ONAN, 50/67 MVA, 132/13.8/6.6 kV, Ynyn0d1 connection), the maximum voltage between the medium-voltage (MV) winding and ground, in case of a 200 V impulse applied to the high-voltage winding, is around 20.3 V; the voltage transferred to the tertiary winding reaches 8.1 V. For the second type (type TTUS-ONAN, 54/73 MVA, 110/15/6.6 kV, Ynyn0d1 connection), the voltage transferred to the MV winding reaches 21.1 V; the voltage transferred to the tertiary winding is 11.9 V. The laboratory tests validate the proposed analytical and simulation model.

The paper deals with the recording and analysis of electric quantities waveforms (voltages and currents) from the components of an electro-energetic group. The quality parameters of energies (and powers) are determined in distorting and unbalanced regimes. Based on the relations used for the determination of the quality factors of electric quantities and respectively for the determination of the active and reactive powers, an analysis is made. It is concerned with the waveforms from: the main generator stator, the auxiliary generator stator before the fully controlled rectifier with thyristors and from the main generator rotor (after the rectifier). Possible interdependencies between these quantities are determined. The reversed power circulations are explained, along with their possible causes. The performed analysis shows that it is necessary to perform a permanent local surveillance of the energy sources from a power system, watching on the power quality parameters