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Inrush current is still a persistent problem affecting the quality of the power system. This paper presents the theoretical aspects of this transient phenomenon, the simulation of the phenomenon for prediction purposes and its measurement in a test laboratory. In the operation of power transformers, there may also be cases where electrical phenomena affecting the operation of transformers may overlap. When power transformers are in operation, there may also be cases where electrical phenomena affecting their operation overlap. This paper includes a study describing such a situation, where the maximum value of the inrush current is amplified by the fact that the series resonance condition has been met. The intersection of these electrical phenomena resulted in internal and external electrical discharges that led to the overhaul of a 440 MVA transformer; the description of this situation is based on field data. The paper focuses on real information and situations that support the development of a maintenance management schedule based on accurate and up-to-date data. The information presented in this paper will be particularly useful to personnel specializing in power transformer design and/or those monitoring/operating high power transformers in the energy sector, but can also be a teaching aid for students interested in such transient phenomena. [ABSTRACT FROM AUTHOR]

This study presents issues related to electromagnetic pollution and the level of magnetic field radiation occurring around conductors used for electricity transmission and distribution. The fact that modeling and simulation are the most efficient methods of optimization, considering the cost–benefit ratio, was the premise of this work. This paper proposes the performance of a complex analysis, carried out in a comparative manner, which includes physical tests and simulations in the existing field around transmission and distribution cables used in transformer substations. In the first stage, the level of the magnetic field existing near the conductor carried by an electric current was tested (measured), and a virtual model was then designed to simulate the field in conditions similar to those of the test. The results obtained from the simulation were analyzed in comparison with those obtained by testing. The maximum permissible limits of exposure to an electromagnetic field, which are regulated by Government Decision HG 520/2016 of 20 July 2016 and Directive 2013/35/EU of the European Parliament and of the Council of 26 June 2013, were used as the reference to formulate conclusions for both situations considered. These comparisons were intended to determine the level of exposure to electromagnetic fields existing in places where electricity transmission/distribution conductors are located. Energy sustainability exists due to the versatile properties of the conductors, with the energy transmission and distribution network being functional regardless of the source of energy production. [ABSTRACT FROM AUTHOR]

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.

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.