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1
Content available remote

Time-Frequency Analysis of Mechanical Vibrations of the Dry Type Power Transformer Core

100%
Borucki S.
Acta Physica Polonica A
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2011
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vol. 120
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issue 4
571-574
EN
The paper presents research results referring to the development of a non-invasive method of assessment of the power transformer core technical condition based on the analysis of the mechanical vibrations registered. It characterizes the power object under study, the measuring system used and the developed methodology of assessment of the core pressing degree using the vibroacoustic method. The original results of the time-frequency analysis of the vibroacoustic signals presented in the paper were obtained during switching on a real 800 kVA dry type power transformer in laboratory conditions. The analysis of the signals registered was carried out for three states of its operation: the core pressed by the manufacturer, the core with loose screws fixing the upper yoke and the core with separated upper yoke beams.
2
Content available remote

Vibroacoustic Measurements in a Transient State οf Transformer Operation

100%
Borucki S.
Acta Physica Polonica A
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2009
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vol. 116
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issue 3
277-280
EN
The subject matter of this paper refers to the assessment of the technical condition of a power transformer core and windings based on vibroacoustic measurements taken during a transient operation state of the appliance diagnosed - at a transformer unit switch on. The paper presents preliminary results of the research work carried out, which aims at elaborating a new diagnostic and assessment method of the degree of the transformer core and winding pressing using the so-called modified vibroacoustic method. The paper characterizes the measurement path and the assessment method of the core and winding pressing degree based on the selected analyses of the vibroacoustic signal registered. The original research results presented in the paper were obtained at a real 400 kV A power transformer switch on in laboratory conditions - for a regular operation condition and for modeled core damage.
3
Content available remote

Solving a Set of Spherical Equations for Localization of Partial Discharges by Acoustic Emission Method

51%
Boczar T., Witkowski P., Borucki S., Cichoń A.
Acta Physica Polonica A
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2015
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vol. 128
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issue 3
299-305
EN
This article deals with the subject matter of improvement of the acoustic emission methods used for location of partial discharges, which may occur inside power transformer insulation systems. Analytical solutions of spherical equations for location of partial discharge generation using the acoustic method were shown in detail. Presented in the article method of solving the assumed equations is based on the analytical method and matrix notation. Theoretical considerations and later the measurement-based verification refer to the use of the triangulation method for location of the occurrence of partial discharges. The results of the scientific and research works that have been presented in this article are the next stage of research aimed at development of on-line diagnosis system for insulation systems of electrical equipment, allowing for detection, measurement and identification of forms and locations of partial discharges using the acoustic emission method.
4
Content available remote

Diagnostics of the Core Mechanical Construction Based on Vibroacoustic Measurements and Distribution of Temperature Field in Transformer Magnetic Circuit

51%
Borucki S., Cichon A., Boczar T.
Acta Physica Polonica A
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2015
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vol. 128
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issue 3
306-309
EN
Subject matter of this article concerns the results of research works on the development and use of the vibroacoustic method to evaluate technical state of transformer cores. The article presents obtained measurement results of transformer mechanical vibration for two cases of its operation: with twisted and loosened core. In order to demonstrate negative effects of operating a transformer with a loosened core, this publication presents thermographic images showing temperature distribution on its magnetic core. The article characterises the examined transformer, employed measurement system and methodology of the completed experiment. The vibroacoustic and thermographic measurements were carried out during idle work of the transformer. Core vibration was registered for three measurement axes: 0X, 0Y and 0Z. Completed tests have proven that loosened screws pressing the core cause evident increase in the value of magnetic core vibration acceleration. At the same time, the temperature rises by more than 25%.
5
Content available remote

Analysis of Acoustic Signals Interfering Diagnostic Measurements of Electric Power Transformer Tap Changers

51%
Boczar T., Cichoń A., Borucki S., Szczyrba T.
Acta Physica Polonica A
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2013
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vol. 124
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issue 3
387-390
EN
Subject matter of this paper applies to improvement of acoustic emission method used in the diagnosis of on load tap changers of high power transformers. During measurement of acoustic emission signals generated by damages or defects, which can appear in insulation system and in the power transformer tap changers, various forms of noise signals may occur. Interferences occurring during measurements under laboratory and under industrial conditions can be generated either by sources placed inside the studied electric power device or they can be emitted in their immediate vicinity. Sources of interfering signals are physical phenomena of a mechanical, electrical or acoustical nature. Interferences appearing during measurement of acoustic emission pulses generated by electrical discharges and other types of defects that overlap the measured waveforms may result in their distortion. As part of the research conducted, the results of which are presented in this paper, following was subjected under consideration: measurements of acoustic noise signals generated by partial surface discharges occurring on support and bushing insulators were performed.
6
Content available remote

Analysis of Ionizing Radiation Generated by Partial Discharges

51%
Zmarzły D., Nagi Ł., Borucki S., Boczar T.
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vol. 125
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issue 6
1377-1379
EN
This paper presents the preliminary results of the performed experiment, based on common phenomenon of partial discharges. A simple Geiger-Muller counter (DP-66M) was used for measurement of a dose of ionizing radiation, which is accompanied by partial discharges. Values from which the radiation intensity was dependent could be controlled individually: the distance between measurer and source, as well as the voltage generating partial discharges. The obtained results indicate that in the examined phenomenon, significant dose of X-ray radiation is present. According to the Kramers-Kulenkampff theory, it depends also on the atomic number of elements involved. Using MATLAB software, the obtained data were compiled to develop suitable theory for further research study. There was also implemented fuzzification for the fuzzy logic, and the effect was the capability of forecasting radiation doses according to the fixed variables for a given material, where partial discharges were generated.
7
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The Critical Evaluation of the Vibroacoustic Criteria Used in Poland to Diagnose of Power Transformer Cores

51%
Borucki S., Cichon A., Boczar T., Zmarzly D.
Acta Physica Polonica A
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2013
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vol. 124
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issue 3
391-394
EN
The subject matter of this article concerns the diagnostic test results of transformer cores by measuring and analysing vibroacoustic signals registered during their normal operation. The main objective of this research study conducted by the authors, the results of which are published in this paper, is a critical analysis of vibroacoustic criteria, which are adopted in Poland nowadays, and based on which, the assessment of the core technical condition is performed. This article presents exemplary results that were obtained on two twin units of type TET 8509 with a power of 40 MVA. The paper specifies diagnosed structures, the measurement system applied, and the currently used methodology to assess the degree of core loosening. To determine the efficacy and assessment accuracy of the applied vibroacoustic criteria, correlation between mechanical vibration measurements of the tested transformer tanks and results obtained by gas chromatography was performed.
8
Content available remote

Modeling of Acoustic Emission Signals Generated in On Load Tap Changer

51%
Cichoń A., Borucki S., Wotzka D.
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vol. 125
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issue 6
1396-1399
EN
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.
9
Content available remote

Selecting Sensor for On Load Tap Changer Contacts Degree of Wear Diagnostics

51%
Cichoń A., Borucki S., Berger P.
Acta Physica Polonica A
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2013
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vol. 124
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issue 3
395-398
EN
Results of scientific research works considering selection of measuring transducer applied for registration of acoustic emission signals generated by on load tap changers are presented in the paper. During the coupling process acoustic emission signals are generated by: the mechanical setup of tap changer, contacts operation, and other phenomena. For most on load tap changers types, the working medium is insulation oil in which the acoustic wave being formed propagates to the steal tank. There exists a possibility to register acoustic emission signals with a piezoelectric transducer attached to the outer tank surface or with a hydrophone immersed in the oil. Acoustic emission signal obtained in such manner contains information which describes operation of the power tap changer and the selector. A comparative analysis of acoustic emission signals generated by on load tap changers working under laboratory conditions, with applied measuring transducers with different transmittances, is presented in the paper. The comparative analysis was performed in order to determine their suitability for on load tap changers technical condition diagnosis. Based on the results achieved, one transducer which allows the registration of acoustic events generated during on load tap changers operation was selected.
10
Content available remote

Analysis of Optical Radiation Generated by Partial Discharges on Insulators

51%
Frącz P., Boczar T., Borucki S.
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vol. 125
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issue 6
1360-1367
EN
Results of measurements of optical radiation emitted by partial and complete electrical discharges occurring on a bushing insulator model placed in air are presented in the article. Registration was performed using a spectrophotometer, enabling for measurement of optical radiation in the range from 270 to 1700 nm. Detailed characteristics of spectrophotometer are presented in our previous paper. The primary objective of the laboratory tests was to evaluate the impact of supply voltage changes in the range from 0 to 0.99 U_{b} (breakdown voltage) on the intensity and spectral character of the optical radiation emitted by partial discharges generated on the porcelain insulation surface of the bushing insulator. In the scope of studies analyzes of the effects of voltage changes on the obtained spectral waveforms were performed, whereby voltage increase and reduction was examined separately. Additionally, measurements and analyzes carried out included impact estimation of the time period as the voltage was applied to the high-voltage electrodes on the course of optical phenomena related to the generation of partial discharges.
11
Content available remote

Analysis of Interference Signals Generated by Vibroacoustic Vibrations of Transformer Cores

51%
Boczar T., Borucki S., Cichoń A.
|
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vol. 125
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issue 6
1355-1359
EN
The article deals with the subject matter referring to the interference that may accompany measurements of vibroacoustic signals, generated by electric power transformers, taken by using the acoustic emission method under industrial conditions. Paper concerns measurement and analysis of internal, acoustic type disturbances, including the magnetostrictive vibrations of plate sets within the transformer core, caused by changes in the magnetic flux. Paper presents measurement results of acoustic interfering signals and results of analyses made in the frequency and time-frequency domains. Power spectral density, MUSIC pseudospectra, two- and three-dimensional short time Fourier transform spectrograms, continuous wavelet transform scalograms, discrete wavelet transform, and quantities of energy transferred are included in the paper.
12
Content available remote

Repeatability Estimation for Vibration Measurement Results of Power Transformer Core

51%
Borucki S., Cichon A., Skubis J., Boczar T.
|
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vol. 125
|
issue 6
1299-1302
EN
The subject matter of this paper refers to the diagnostics of a transformer core, based on measurements and analysis of vibroacoustic signals registered during their normal operation. The paper presents results of the research aimed to evaluate the repeatability of vibration measurements for power transformer core. Recording of vibroacoustic signals was performed under laboratory conditions on dry-insulated transformers. The study concerned evaluation of changes in vibroacoustic indicators of the transformer core during operation with a turned and loosened core. Conclusions from the measurement results were drawn on the basis of the parametric test of significance derived from the variance analysis for many means of single classification basing on the Fisher-Snedecor F-distribution.
13
Content available remote

The Use of 3D Modeling in the Diagnosis of Power Capacitors with Acoustic Emission Method

51%
Boczar T., Błachowicz A., Borucki S., Zmarzły D.
Acta Physica Polonica A
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2012
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vol. 122
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issue 5
796-799
EN
The article presents the issue modelling the partial discharge phenomenon in engineering and scientific environments using hardware-based computer cluster. The authors present the results of research work on the phenomenon of acoustic emission from partial discharge occurring in power capacitors for power factor correction. The work includes the issues presentation and explanation of solutions enabling to create 3D spatial model of power capacitor. The authors proposed a simplified model of an acoustic test object aimed at improving the process of calculating the results.
14
Content available remote

The Wavelet Analysis of the Vibroacoustic Signal Measurement in a Transient State Operation of Power Transformer

51%
Borucki S., Cichon A., Boczar T., Zmarzly D.
Acta Physica Polonica A
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2012
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vol. 122
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issue 5
800-803
EN
The article presents the results of attempts made to develop a non-invasive diagnostic method of a technical state of a transformer's core based on an analysis of mechanical vibrations registered during the start-up of the transformer analyzed. The paper presents a characteristic of the transformer under study, the measuring systems applied and the method developed for assessing the degree of the core loosening. The original results presented in the paper have been obtained under laboratory conditions during tests conducted on an oil transformer of 200 kVA. The analysis of recorded virboacoustic signals was performed by means of discrete wavelet transform for three different operating cases: the transformer with no core defect, the transformer with loose screws of the magnetic circuit of the upper yoke, and the transformer with completely loosen screws of the beam of the upper yoke and the lower core. The signals have been recorded on two perpendicular measuring axes: 0X and 0Y and their measured values were subject to the wavelet analysis.
15
Content available remote

Characteristics of Acoustic Emission Signals Generated by the Contacts of the Selector

51%
Cichoń A., Borucki S., Wotzka D., Szmajda M.
Acta Physica Polonica A
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2012
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vol. 122
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issue 5
804-807
EN
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.
16
Content available remote

The Analysis of Mechanical Vibrations and Acoustic Pressure Level οf a Transformer Model

51%
Boczar T., Borucki S., Cichon A., Lorenc M.
Acta Physica Polonica A
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2008
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vol. 114
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issue 6A
A-21-A-26
EN
The paper presents the results of vibroacoustic investigations and the measurements of the acoustic pressure level (noise) of a transformer model. The measurements were taken at a full transformer load in two operation conditions: at a producer packeted core and at unpacketed core. Unpacketing consisted in loosing the screws pressing the particular core plates. Mechanical vibrations were registered and the acoustic pressure level was measured. The vibroacoustic analysis results are presented in the form of frequency spectra and the results of the acoustic analysis of the transformer under study are shown by determining corrected values of the acoustic pressure level and by a frequency analysis.
17
Content available remote

Results of Optical Signals Analyses Emitted by Electrical Discharges Recorded with UV Camera

45%
Frącz P., Boczar T., Borucki S., Cichoń A., Zmarzły D.
Acta Physica Polonica A
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2012
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vol. 122
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issue 5
814-817
EN
In the article results of measurements and analyses of the optical signals emitted by electrical surface partial discharges occurring on bushing and post insulators, recorded with UV camera during tests under laboratory conditions are presented. The carried out research was to determine the effect of the distance between the insulator's electrodes and the voltage value on the number of partial discharges.
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