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Single phase currents and voltages were acquired from the primary winding of a locomotive transformer. Four operating regimes were considered (acceleration, running at constant speed, normal and respectively regenerative braking). 6 data sets consisting of 3 consecutive periods were considered as representative for this study and analyzed: one per each of the first 3 mentioned operating regimes and...
The paper is focused on finding appropriate and systematic procedures of denoising highly distorted small currents with significant “signal to noise” ratios and on evaluating the denoising effects over the power quality (PQ) indices. Real currents were acquired from 2 consumers placed in a small industrial hall with highly variable power consumptions. Denoising procedures relying on wavelet based...
The paper deals with the behavior of a medium / low voltage transformer (MV/LV), for a non-sinusoidal consumer placed in the transformer's secondary winding. The analysis is performed using the Discrete Wavelet Transform (DWT). The monitoring is realized with two data acquisition systems, briefly described in the paper. Problems associated to the conducted and radiated emissions are addressed and...
The paper is focused on finding appropriate procedures of denoising electrical signals (SN) acquired from the secondary winding of the excitation transformer in a large power group and evaluating their benefits. The signals were affected by white Gaussian noise with relatively high Signal to Noise ratios. The currents have significant harmonic contents (total harmonic distortions exceeding 25%). Two...
The capabilities related to active filtering of the Stationary Wavelet Transform — SWT were evaluated considering 3 Daubechy wavelet mothers. Firstly a study on errors was performed on synthetic waveforms. The waveforms were obtained from sinusoids polluted by single harmonics with orders from the range 3…40 and magnitudes, respectively phase differences varied in a systematic manner. The differences...
Computational techniques conceived to improve the efficiency of PQ analysis of quasi-stationary signals acquired from the secondary winding of the excitation transformer in a power plant are addressed. Signals of 30 periods (SN) were analyzed. SN were polluted by white Gaussian noise and "arithmetic average" signals (AS) of one period length were computed for 2 reasons: (a) simpler noise...
The loadbreak cutout control is most often performed from the zonal load dispatcher level. The system presented in this paper performs the remote control and permanent monitoring of some loadbreak cutouts which run on a 20kV power line. The monitoring and control is directly carried out by the zonal load dispatcher. This remote control alternative provides more operativity and safety in decision making...
Special preprocessing techniques for denoising quasi-stationary signals (SN) acquired from the secondary winding of the excitation transformer in a power plant are addressed. Sequences of 30 periods were analyzed. SN were polluted by white Gaussian noise and “average” signals (AS) of one period length were deduced. Because vectors of samples were handled, corrective measures (CM) were applied firstly...
A complex data acquisition system used in the monitoring and diagnosis of an entire large power group delivering electric power in a power system is presented. The tests are performed with three independent synchronized data acquisition systems able to acquire up to 24 electrical quantities. The hardware and software solutions are described. Considerations on the preprocessing of data and preliminary...
The results of the measurements concerning the electric quantities from an auxiliary generator, a three-phase rectifier controlled by thyristors, and a main generator from a power group, performed using an integrated measuring system are presented. The modality to determine the power quality parameters is detailed. The analysis allows the detection of possible undesired distorting regimes, with serious...
The paper deals with the analysis using Wavelet Packet Transform (WPT) and Fast Fourier Transform (FFT) of synthetically generated signals. The signals are initially sine waves of 10 periods with linearly decreasing/increasing magnitude M. M varies according to a constant slope G. The studied absolute difference between the final and initial values of M belongs to the set {2,5, 5, 7.5 and 10}% from...
Aspects of evaluating even harmonics by exploiting characteristics of energies produced by them in the terminal nodes of a tree determined with the WPT are approached. Two wavelet mothers (WM) were analyzed. db14 involves smaller runtimes, but the per-node weights of “node-dominant” harmonics have often smaller values when compared to those yielded by db20. For both WM, 14 nodes from the final level...
The paper deals with the behavior of a medium voltage/low voltage transformer (MV/LV), used to power the excitation circuit of a power group. The transformer's load is nonlinear, therefore inducing strong non-sinusoidal regimes in the primary and the secondary windings of the transformer. Non-sinusoidal regimes are due a thyristor rectifier used to power excitation. Two distinct situations are analyzed,...
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...
The paper deals with the problems introduced by a fully controller rectifier with thyristors (FCTR), used in the supplying circuit of a power plant's excitation winding. The rectifier is supplied from the secondary winding of a 3.256 MVA, 24 / 0.65 kV power transformer (PT), in a schema modified with respect to the excitation supplying from an auxiliary generator. The use of PT supplied from the main...
The paper presents a method for monitoring and diagnosis of the effects yielded by the non-sinusoidal regime over the voltage transformers operating in a power group. The analyzed schematic structure is presented along with all its components. Information on the designing, construction and implementation of a data acquisition system (DAS) are presented, along with the interface for data visualization...
The paper studies high order harmonics in distorted regimes with fast variable loads. Our experimental setup uses a three-phase load, built in laboratory by connecting in pairs, in different configurations, several laptops (from different manufacturers) across phases of a three-phase system. Our original dedicated data acquisition system acquired single phase waveforms, each of 5 periods, corresponding...
The paper deals with problems related to non-sinusoidal regimes introduced in the supplying network by a laptop and respectively by a set of laptops connected in various configurations. The three-phase voltage(s) and current(s) were acquired with an original data acquisition system with a sampling frequency of 19,200 Hz. Harmonic decompositions up to an order of 192 (corresponding to a frequency of...
The paper analyzes the behavior of a three-phase consumer, consisting of several personal computers connected to a transformer's secondary phases. The modalities of monitoring and recording of electrical quantities are presented in this work. The structure of the consumer is described. The recorded waveforms are analyzed. The Fast Fourier Transform (FFT) analysis allowed for the decomposition of the...
The paper deals with the immunity for radiated emissions and compliance with international standards for electromagnetic compatibility (EMC) measurements. EMC standards for GTEM Cell, GTEM Cell construction, GTEM model, generation and distribution of electric and magnetic field inside the GTEM Cell, equipment under test (EUT), radiated emission measurement scheme, are presented. Mobile phone immunity...
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