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Wavelet transformation is one of the most popular tools for acoustic signal analysis. It provides good resolution both in time and frequency domains as well as wide choice of mother wavelets -- this makes wavelet transformation a choice when flexible approach is required. However, selecting parameters of analysis can be difficult, especially regarding mother wavelet as different mother wavelets have various properties regarding number of vanishing moments and symmetry. This paper presents studies to determine the possibility of on-load tap changer wear detection by applying wavelet transformation. In research, different mother wavelets were selected and their usefulness was examined. Signals to be analyzed were obtained during on-load tap changer operation in different mechanical conditions -- simulating devices wear in service. All measurements were performed on model very similar to real industrial on-load tap changer. Tests were conducted in controlled laboratory environment, reducing most of the possible disruptions. [ABSTRACT FROM AUTHOR]

Operation of modern wind turbines generates infrasound noise which is known as potentially harmful for humans. In presented study, measurements of infrasound noise generated by operation of five vertical axis, building mounted, small wind turbines were conducted. Measurements were taken in urban area at several points and different distances from the installation. Analyses were performed to determine the level of emitted infrasound noise in vicinity of the installation. Comparative analyses were carried out and the achieved results were referred to the limits of sound pressure intensity level of infrasound signals as specified for the working environment in accordance with the Polish standard PN-Z-01338. [ABSTRACT FROM AUTHOR]

The paper deals with mathematical modeling of acoustic emission signals which are generated in on load tap changers. In power engineering area acoustic emission method is commonly used for diagnosis purposes. Authors in their research works apply it for detection of defects occurring in on load tap changers, which are important elements of power transformers. The acoustic emission method is based on measurements performed by use of wideband piezoelectric transducers that are mounted on transformer tank surface. The registered signal is then analyzed in the time, frequency, and time-frequency domains or is evaluated with computer expert systems for diagnosis purposes. Depending on indicators device technical condition can be determined. The contribution given by the authors in this paper is proposal of a mathematical model, which describes envelope of the measured acoustic emission signal. [ABSTRACT FROM AUTHOR]

Subject matter of this paper deals with issues of the environmental impact of infrasound noise associated with operation of low-power wind turbines. It is now the current and relevant problem for both the cognitive and utilitarian standpoint. There is now a considerable growth in the number of such installations in Poland, Europe and in the world, due to the possibility of locating them on existing building roofs in heavily urbanized areas, and without having to build additional supporting structures. As part of the study, measurements of low frequency acoustic signals generated during operation of micro turbine equipped with a rotor of vertical axis of rotation relative to the wind direction have been performed. Analyses were carried out in order to determine the impact of wind speed and selected meteorological parameters on the level of infrasound signals emitted by the test turbine. In addition, frequency analysis of the recorded signals was performed. Then, the obtained results were subjected to comparative analysis. In summary, the achieved results were referred to the limits of sound pressure intensity level of infrasound signals as specified for the working environment in accordance with the Polish Standard PN-Z-01338. [ABSTRACT FROM AUTHOR]

The subject area of this article applies to study of infrasound signals generated by the work of modern wind turbines. Infrasound noise measurements were conducted in accordance with assumptions of the EN 61400-11 standard. The object of study was a newly commissioned wind farm with a total electrical power equal to 30 MW. The considered power station consisted of 15 new wind turbines, each with a capacity of 2 MW. Scope of the analysis performed included designation of time runs, depicting temporal changes, and designation of frequency spectra of the recorded infrasound signals. Evaluation of the impact of changes in wind speed was made. Moreover, the scope of analysis, performed in this field, concerned assessment of the impact on the obtained results values of meteorological parameters related to the applied measurement system. Values obtained from measurements were related to and compared with the limits specified in standards and regulations existing in this field. [ABSTRACT FROM AUTHOR]

An important part of electric power transformer is the on load tap changer which enables for voltage regulation in the network. Due to high level of failure frequency of these devices it is necessary to look for new diagnostic methods which enable for theirs technical state estimation under transformer normal operating condition. Presently at the Electric Power Institute at Opole University of Technology there are works in progress aspiring to determine the application possibility of the acoustic emission method for on load tap changer diagnosis. Results of scientifically-research works aiming to characterize the acoustic emission signals generated by a separated selector are presented in the paper. Measurements have been performed in a setup with a model of on load tap changer type VEL-110-27 from ELIN. Acoustic emission signals generated by the selector have been analyzed in detail. Analysis of the time-frequency components of signals generated by on load tap changer has been carried out with the short time Fourier transform and continuous wavelet transform. Based on the comparison outcome of acoustic emission signals generated by the power changer and by the selector two measuring paths endowed with wide band contact transducers have been proposed for the practical application. [ABSTRACT FROM AUTHOR]

Paper presents definition of a mathematical model describing acoustic emission signals generated by partial discharges occurring in oil immersed electric power transformers. Time runs, power spectral density graphs and spectrograms of acoustic emission signals generated in experiments, performed under laboratory conditions, and of equivalent signals, calculated on the basis of the mathematical model, are presented. Furthermore, results of numerical simulations of acoustic pressure distribution inside a tank filled with insulation oil are presented in the paper. In the center of the tank acoustic emission wave sources were placed, each generating signals described by the model developed. [ABSTRACT FROM AUTHOR]

Results of a numerical simulation of an acoustic wave that propagates in a spherical object filled with insulating oil are presented in the paper. The sinusoidal acoustic wave is generated by an electro-acoustic transducer mounted in the middle of the object. Presented results depict acoustic pressure distribution within the transient and the steady states in a two-dimensional object. Furthermore, comparison of short time simulations adapting different mesh element size is presented. [ABSTRACT FROM AUTHOR]

Results of a measurement and analysis of vibro-acoustic signals generated by two low power vertical-axis wind turbines that are installed on the roof of the Electric Power Institute at Opole University of Technology are presented in the paper. The study considers a Darrieus and a Savonius type wind turbines of rated power 1 kW each. For registration of the vibrations of the turbine mast three uniaxial accelerometers and a measurement equipment from Brüel & Kjær were applied. The measurement setup is presented in the paper. A comparative analysis of the registered data in the time and time-frequency domains was performed. Results depict changes in the recorded signals in time and frequency under different meteorological conditions, i.e. for different wind speed values. Based on the achieved results significant differences in the mast vibrations of the two kinds of wind turbines were stated. [ABSTRACT FROM AUTHOR]