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Signals acquired from an industrial environment with many sources of electromagnetic interferences may be polluted by white noise. Polluted data segments with many steady consecutive periods can be used (sometimes unsuccessful) for the estimation of a denoised period from the steady acquired data by using the mean signal method. For data segments with at least 4 periods, when only certain segments (shorter than a period) can be considered steady, hybrid algorithms can be used to automatically evaluate the power of noise and afterward to perform the noise removal by using wavelet thrashing trees. This paper deals with 2 additional denoising techniques. The 1-st one is based on the Wavelet Package Transform and allows for the separation of the noise components which pollute a data segment of at least one period. The second approached denoising technique is also addressing one period data segments and estimates firstly the power of noise by using the energies of the vectors of details from the first 2 levels of a tree used by decompositions with the Stationary Wavelet Transform. The estimated power of noise is afterward used to establish the number of levels in the wavelet thrashing trees. In this last stage, two wavelet mothers were used. Simulated and real test signals were used and performance comparisons were performed.

Acquired electrical waveforms can be affected by white noise. The 1-st part of the paper analysis deals with the denoising of multi-period steady signals by using 3 methods: mean signal method, an original method relying on wavelet packet trees and the method implemented by the wavelet-based Matlab function wden. The signal length influence over the mean signal method’s accuracy is studied. The results yielded by the other 2 methods are also analyzed considering signals with 7 periods. Afterward the wavelet-based methods are used to denoise segments of 7 periods with linearly variable magnitudes (ascending or descending) for 3 different slopes. Artificial test signals, with rich harmonic content, were used. They were polluted by sets of 10 white noises with different powers. Maximum absolute deviations and mean square root deviations were computed considering the original signals, before pollution, versus the corresponding denoised signal. The metrics were computed relative to the maximum absolute value of the noise and allowed to determine the most accurate method.

Wavelet packet trees represent a topic which grows in popularity when it comes to analysis of electrical waveforms. It allows for time-frequency analysis providing information on narrower ranges of frequency (as compared to the faster Discrete Wavelet Decomposition), but the computational resources are significantly greater than that involved in other types of wavelet-based analysis. In order to allow for this type of analysis to be usable in real-time applications, that is – to reduce the runtime, original algorithms were conceived and tested. In the first part of this work, previously implemented algorithms are briefly described, along with their pros and cons. Afterward, a new runtime optimization algorithm is proposed. Details on data structures, workflow, tests and study of errors are provided. This algorithm diminishes with up to 59% the runtime required by the application of the superposition theorem in order to evaluate the contribution of clustered harmonics using WPT.

The paper is concerned with an equipment used to monitor power transformers. The equipment is working in an environment where electromagnetic interference may occur, being able to transmit data related to the transformers operation. The monitoring equipment was submitted to tests for conducted emissions. The initial tests revealed that the compliance with the norms from the standard related to conducted emissions for this type of equipment was not achieved. Several measures had to be taken to pass the tests. The first step was to reduce the conducted emissions associated to the inputs in the supplying source. Therefore a ferrite filter was designed and implemented, being placed at the equipment general supplying input. The conducted emissions were again evaluated and again the tests were failed. Consequently a network filter had to be designed and placed. Finally the compliance with the norms relative to conducted emissions was obtained.

Single phase currents and voltages were acquired from a substation used to supply power lines for railway transport. Different operational contexts were addressed (variable types of locomotives and trains, some of them being simultaneously nearby the substation). Firstly an evaluation of the background noise was performed by using either the mean signal or a thrashing tree. Fast Fourier and Wavelet Packet Transforms were used to evaluate the harmonic spectra and the major types of Root Mean Square quantities. The computed THD revealed significant distortions of the analyzed waveforms. The results yielded by different methods were compared. A good convergence of methods was reached in most of the cases and explanations for the differences recorded for the rest are proposed. Instantaneous values of the fundamental harmonic and global distortions were evaluated with the Stationary Wavelet Transform, allowing the evaluation of maximum/RMS values for currents/voltages to be injected when using active filtering.

The paper is concerned with an intuitive approach of harmonics evaluation by using the Wavelet Packet Transform. Conceptual argumentation of simple and reliable algorithms is provided firstly. Two wavelet mothers (WM) were analyzed in order to see which of them allows for a simpler and faster implementation, involving less computer resources simultaneously with improved accuracy. The first one (using a Daubechy WM relying on 28 coefficients - known as db14 in Matlab) involves smaller runtimes for decomposition, but the per/node weights of “node-dominant” harmonics have often smaller values when compared to those yielded by db20. For both analyzed WM, 8 nodes from the final level could be grouped in pairs considering the principle: energies of nodes in a group are affected only by a pair of harmonics and the paired corresponding harmonics do not affect any other node except those from that group. The weights of energies generated by signals polluted by a single harmonic were found to be almost identical for a certain node, irrespective to the magnitude or phase of the analyzed signals. On the other hand, when pairs of harmonics (correlated by the nodes where their energies can be found) act simultaneously, variations of the above mentioned weights were recorded. Therefore a harmonic evaluation based on the solving of 2×2 linear systems yields errors and sometimes negative energies leading to values for harmonic magnitudes out of the real numbers' space. In this context we conceived and implemented another algorithm, based on a lookup table technique. For the “non-paired” harmonics another rule was detected. Groups of 4 nodes (quadruples) are affected only by groups of at most 4 harmonics. Three quadruples were found. For one of them only the energies of 3 nodes a required, because only 3 harmonics influence the nodes from the quadruple. Good mean values of errors related to the harmonic magnitudes evaluation were obtained after running sets of 50 randomly polluted signals for all pairs of odd harmonic orders from the range 3…40. Most of the absolute percent errors higher then 1.5% from the RMS value of the polluted signal in the case when the lookup table technique was used were found to be associated to inversions in paired harmonics (that is the magnitudes of harmonics were computed as being switched between the members in a harmonic pair). This is due to the symmetry of some components of the matrices used for calculation and perhaps can be solved by using more accurate values for them.

The paper is concerned with aspect on the realization and testing of RC active filters. The analysis is focused on low-pass second order Butterworth filters with different quality factors. They are used in industrial applications where the high frequency components must be removed from the signal spectrum. The frequency characteristics are plotted for the analyzed cases using SPICE. Based on the results yielded by the calculation of RC elements' parameters and respectively by simulation, filtering modules were realized. They make possible a fast modification of the quality factor. An analysis in time domain was also performed. The experimental results came out to validate the results yielded by simulation.

The paper presents the features of passive filters and some of the topologies used for the improving of power quality. One has in view aspects on the designing of passive filters tuned for some harmonic components. One presents some recordings and numerical simulations made over the electric signals from a substation used for the supplying of a d.c. line of 600 V. Based on the obtained results one proposes solutions for passive compensations with the consideration of a number of filtering components that depends on the compensation necessities. In order to verify the compensation efficiency, through SPICE simulation, one estimates the effects of compensation correlated with the number of passive filtering cells.

The paper presents some practical considerations and experimental results obtained by the exploitation of a tram that has an electric driving system with an improved technological solution. One presents the technological solution using chopper that substitutes the initial accelerators of the tram. Some aspects concerning the operation in running and respectively in braking regimes in the new configuration (including the regenerative braking regime) are discussed. Some considerations with respect to the electromagnetic compatibility problems and modalities to improve it are made. The recordings of the current and voltage waveforms, during the normal running stage, when the tram climbs a ramp and respectively goes down on a slope are presented and explained. The experimental determinations revealed that the system was designed correctly, in order to support all the operational conditions that could appear in its exploitation.