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.

The paper deals with the components design and the simulation of a photovoltaic power generation system using MATLAB and Simulink software. The power plant is composed of photovoltaic panels connected in series and parallel strings, a DC-DC boost converter and a three-phase inverter which connects to a 0.4 kV three-phase low voltage grid and a 20 kV medium voltage grid by means of a step-up transformer. The DC-DC boost converter uses a MPPT controller and the inverter uses a control method based on d-q theory with a PI current regulator. Some cases for which the dynamic behavior of the configured photovoltaic system presents interest are simulated. They address the solar irradiance and temperature change.

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.

Data acquisition and recording systems are very useful for monitoring industrial processes or electrical events in power plants, electrical signal analysis to reduce electricity consumption etc. This paper deals with a customized data acquisition and recording system for an electrical power cabinet that ensures the power supply of a three-phase consumer. The module for the acquisition, storage and transfer of the data related to monitored electrical signals performs the synchronous sampling of eight analog inputs (voltages and currents) with a high sampling frequency. The firmware of this module performs the synchronous sampling of the analog inputs, temporary data storage and their transfer into owner format compatible with specialized programs for analysis using Discrete Wavelet Transform or Fast Fourier Transform. The presented data acquisition and recording system has a Windows compatible associated software application which handles the equipment configuration, automatic transfer of the acquired data and their storage into a database available for other applications. The work focuses on software design, but also presents experimental results obtained using the presented data acquisition and recording customized system.

This paper presents measurements of power quality indices for a static excitation system composed of a transformer and a controlled rectifier bridge in a power system generator group and the corresponding MATLAB/Simulink simulation. Replacing the old auxiliary excitation generator eliminates the disadvantage of using electrical machines with inertial moving masses and wear over time, but with the price of facing two important problems: the line voltage notching due to thyristor switching and the line current distorting. Theoretical aspects of line notching and several solutions for compensation strategies (and their limitations) are discussed. The MATLAB/Simulink model made possible the implementation of the solution selected to deal with these problems and to evaluate its effectiveness based on the results.

The paper focuses on the joint analysis (using Wavelet Packet Transform (WPT)/Discrete Wavelet Transform (DWT) and respectively Fast Fourier Transform (FFT)) of voltages and currents acquired from a generator operating in the Power Plant Turceni, Romania, as a major stage in designing the components of an active power filter (APF). When fast methods, providing accurate results are used, fundamental active currents can be calculated and subtracted from the load currents. Afterward the results are to be inverted in order to obtain the reference currents for the APF. Firstly brief information about the algorithms implementing DWT/WPT, respectively FFT are given. Afterward a study of errors associated to the evaluation of the three major RMS (for fundamental frequency, for distortions and total) is presented. The errors were yielded when analyzing signals with known characteristics (sinusoidal and polluted by a single harmonic), by using 2 interpolation methods (IM): spline and respectively shape-preserving piecewise cubic interpolation. Different numbers of calculation points and disjoint ranges of harmonic orders were used. Comparisons were made between results yielded by the same method but using different simulation parameters, respectively FFT versus DWT (WPT). Two sets of data from the power plant were analyzed. The 1-st one had a reduced harmonic content, whilst the 2-nd one presented significant multi-harmonic distortions. The errors in evaluating the total RMS were computed considering a reference calculated with a Riemann sum. For this PQ index, DWT(WPT) records smaller errors in all studied cases. The differences between the values provided by FFT and respectively by DWT(WPT) are very small (<0.21% in absolute values), proving the reliability of both methods. Spline generated better results. For similar memory consumptions, FFT performed very fast, while WPT achieved very good runtimes (2.98×10⁻² sec/period for the calculation of the fundamental's RMS). Smaller mean errors were generated by WPT when evaluating the fundamental's RMS when the fundamental signal was slightly deviated from sinusoidal.