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1
Content available remote

Analysis of Acoustic Wave Propagation in a Power Transformer Model

100%
Wotzka D., Boczar T., Zmarzły D.
Acta Physica Polonica A
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2009
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vol. 116
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issue 3
428-431
EN
Analyses of acoustic wave propagation in a model power transformer are presented in the paper. The acoustic wave is induced by partial discharges that are simulated at predefined coordinates in the core and winding. Propagation of the numerical calculated acoustic wave is analyzed within the transient state. Achieved results indicate that the space and time distributions of the acoustic pressure depend on the induction position. Furthermore, a greater pressure gradient is observed in domains with higher speed of sound while the largest amplitude occurs at the vicinity of the induction position.
2
Content available remote

Characteristic of Acoustic Signals Generated by Operation of On Load Tap Changers

100%
Cichon A., Fracz P., Zmarzly D.
Acta Physica Polonica A
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2011
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vol. 120
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issue 4
585-588
EN
Possibilities of application of the acoustic method for the on load tab changers diagnosis has been presented in the paper. The analysis of measurement results gathered during research works performed under laboratory conditions has been presented in detail. The registered acoustic signals have been analyzed in time and time-frequency domains. The time domain analysis has been performed by presentation of time runs and their envelopes determined by use of the Hilbert transform. Evaluation of the time-frequency components has been performed by use of the short-time Fourier transform, the discrete and the continuous wavelet transforms.
3
Content available remote

Synchronization Study and Introductory Experiment οf Laser-Triggered Surface Flashover in Voltage Pulse

100%
Pan R., Wang J., Sun Y., Sun G., Yan P., Zhang D.
Acta Physica Polonica A
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2009
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vol. 115
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issue 6
1167-1169
EN
With the aim of studying the characteristics of laser-triggered surface flashover in voltage pulse, synchronization problem of laser pulse and voltage pulse should be solved. A single/double harmonic, with wavelength λ of 1064/532 nm, Q-switched Nd:YAG laser is used to trigger the surface flashover. The synchronization problem is solved using a self-made digital delay/pulse generator. The delay time and jitter of Marx's trigger input and output, Marx's trigger output and Marx's output, laser input and output are respectively measured. Based on the result of the delay time and the timing sequence of the laser triggering system, the synchronization of laser pulse and voltage pulse is obtained through adjusting the channel delay time of digital delay/pulse generator. In addition, introductory experiment of laser-triggered surface flashover is carried out using the flat electrodes and columned insulators.
4
Content available remote

An Investigation on Surface and Electrical Properties of Electrical Discharge Machined AISI D2 Tool Steel

100%
Durmus A., Bayram A., Gunes S., Akay S.
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vol. 125
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issue 2
515-517
EN
The effects of pulse-on duration and finishing operation on the surface roughness and electrical resistivity of AISI D2 tool steel machined by the electrical discharge machining process are investigated. Experimental results indicate that surface roughness increased depending on the pulse-on duration. However, after the specific value, surface roughness is decreased. It can be seen that there are no notable effects of the pulse-on duration on the electrical resistivity, but the resistivity values are affected by the heat treatment and the finishing operation. Also, light microscopy and scanning electron microscopy have been used to study the characteristics of the surfaces.
5
Content available remote

Microwave Field Strength Computing for the Resonator Designs and Filters

100%
Radmilović-Radjenović M., Radjenović B., Savić M.
Acta Physica Polonica A
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2016
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vol. 129
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issue 3
289-292
EN
Recent development of microwave pulse generators, which are now capable of delivering very short and very intensive pulses requires properly generalized classical breakdown theory. On the other hand, the trend to design microwave devices as small and compact as possible, leads to a concern about the concomitant breakdown strength of the construction, involving more complicated geometries, such as in microwave resonators and filters. In this paper, several aspects of microwave breakdown field strength in commercially available resonator designs and filters are presented and analyzed. The numerical predictions based on the Slater theorem are compared with the analytical results and predictions of the fluid approach, demonstrating very good agreement.
6
Content available remote

The Application of the Selected Time-Frequency Descriptors Detection of the Acoustic Emission Signals Generated by Multisource Partial Discharges

100%
Cichon A.
Acta Physica Polonica A
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2009
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vol. 116
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issue 3
290-293
EN
The paper presents the comparative analysis results of the acoustic emission signals generated by various forms of partial discharges occurring in multisource systems. Modern methods of the signal digital processing: a short-time Fourier transform and continuous and discrete wavelet transforms were applied for the assessment of the results in the time-frequency domain. The acoustic emission signals generated by partial discharges were registered with a WD AH17 contact transducer by the Physical Acoustics Corporation placed on the external part of the tub.
7
Content available remote

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

100%
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.
8
Content available remote

Electric Field Modelling in Gas-Insulated Substation for Analysis of Conditions for Partial Discharge Phenomena

80%
Florkowska B., Zydroń P., Jackowicz-Korczyński A.
Acta Physica Polonica A
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2015
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vol. 128
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issue 3
319-325
EN
The paper refers to diagnostics problems connected with the presence of partial discharges in gas-insulated substation. The basic stimulus for partial discharges generation is local, high value electric field, greater than the inception one. The numerical simulations of the electric field distribution in the part of the gas insulating system and in the vicinity of the metallic protrusion located on high voltage conductor are presented. Such defects are often present in SF₆ insulated constructions and are the cause of a local increase of the electric field. Theoretical analysis of physical mechanism of partial discharges initiation and development in the case of micro-needle type defects is described.
9
Content available remote

Properties of Acoustic Emission Signals Coming from Partial Discharges Caused by Modeled Sources Immersed in Transformer Oil

80%
Witos F., Gacek Z.
Acta Physica Polonica A
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2009
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vol. 116
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issue 3
422-427
EN
Investigation results concerning acoustic emission signals coming from partial discharges generated by modeled sources are presented in the paper. These sources have been made using different bushing ends (without any extra elements and with a thread or a pike) situated directly in the oil, but without screens typical for partial discharge investigations in a bushing. Measurements have been carried out using own measuring acoustic emission system DEMA-COMP and - in a parallel way - computer-aided partial discharges measuring system TE 571 (produced by the firm Haefely Trench). Fundamental and advanced analysis of acoustic emission signals has been made. These signals were recorded in 20 measuring situations which need to multiple installation of acoustic emission sensors. Conclusions resultant from own originate advanced analysis of signals content description of properties revealed by defined acoustic emission descriptors.
10
Content available remote

Analysis of Properties of Chosen Acoustic Emission Descriptors Describing Acoustic Signals Measured by Means of Acoustic Emission Method within Oil Transformers

80%
Witos F., Olszewska A.
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issue 6
1267-1271
EN
Authors of the paper present investigation results concerning properties of ADP, ADC and ADNC descriptors which have been obtained during measurements made within three oil transformers and then tested also by other methods (electric and dissolved gas analysis ones). Methodology which makes easier an analysis and identification of acoustic emission signals generated by partial discharges is presented. Results obtained by acoustic emission method have been referred to results coming from other measuring methods.
11
Publication available in full text mode
Content available

Measurements of Cu Atoms Diffusion Coefficients in He and Ne - Optimalisation of a Novel Method

80%
Kwaśniewski W., Dzieciołowski K., Adamowicz T.
Acta Physica Polonica A
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2002
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vol. 102
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issue 6
747-757
EN
A novel method based on two-pulse excitation of a hollow cathode discharge to determine metal atoms diffusion coefficients in noble gases was tested in Cu-He and Cu-Ne systems. The excitation conditions such as time duration of the discharge current pulses and configurations of the hollow cathode discharge were checked. Measurements carried out over the wide range gas pressures allowed obtaining the Cu atoms time-decay curves from which the diffusion coefficients were calculated. The values for Cu atom diffusion coefficients of 570 and 310 cm^2 s^{-1} mbar in He and Ne, respectively were in a good agreement with earlier reported data achieved by using the absorption spectroscopy method. The diffusion coefficient of Cu in ^3He, the lighter isotope of helium, was also found to be 670 cm^2 s^{-1} mbar that agreed well with the kinetic theory of gases. To authors believe this value was not reported previously.
12
Content available remote

Uncertainty Evaluation of Measurement Data Processing Algorithm Based on Its Matrix Form

80%
Konopka K., Topór-Kamiński T.
Acta Physica Polonica A
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2011
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vol. 120
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issue 4
666-670
EN
Data processing algorithms are important parts of modern measurement systems. These algorithms are often delivered to the user as complex program and their numerical structure is not known. Therefore also influence of algorithm on processed data accuracy is not known. One of the methods to evaluate uncertainty propagation through algorithm is based on matrix form of algorithm. Coefficient matrix of algorithm represents its numerical operations and it is a basis to algorithm accuracy evaluation. The paper presents a method how to identify this coefficient matrix when algebraic form of the algorithm is known or is difficult to use. Identified matrix form of algorithm is then used to estimate uncertainty propagation through exemplary algorithms. Results are compared with experiments.
13
Content available remote

Decay of Electric Charge on Corona Discharge Polyethylene

80%
Zhang L., Xu Z., Chen G.
Acta Physica Polonica A
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2009
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vol. 115
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issue 6
1197-1200
EN
In this paper, surface potential decay after corona charge deposition has been investigated for low density polyethylene (LDPE) films. We believe that the three ways of electron charge decay on the surface of insulating polyethylene film is reasonable. The factor of neutralizing with opposite charge in air is negligible, and leakage along insulator surface or through the body is much more important for electron charge decay. Both ways are related with surface voltage of the sample. When the voltage is lower than a critical value, surface leakage contributes most. If the voltage is higher than this value, the electron energy on the surface of the sample exceeds the critical value and it is easy to cross the "deep trap". In this situation, the body leakage is more important, and the decay on the surface of sample speeds. That is why there exists decay curve crossing phenomenon.
14
Content available remote

Electron Avalanche Statistics

80%
Ficker T.
Acta Physica Polonica A
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2009
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vol. 116
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issue 6
1018-1020
EN
A solution of the long-lasting problem with anomalous population statistics of pre-streamer avalanches has been proposed in the form of a new generalized probability density function.
15
Content available remote

Measuring Picosecond Flashover in Closing Coaxial Spark Gap Switch

80%
Klüss J., Hällström J.
Acta Physica Polonica A
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2009
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vol. 115
|
issue 6
1004-1006
EN
Flashover voltage and picosecond risetime of breakdown in pressurized SF_{6} gas is studied on a coaxial line. Gas pressure is varied from 1 to 19 bar. The homogeneous field gap has an opening from ca. 0.2 to 0.9 mm, and flashover voltages reach 120 kV. Measurements are performed using a D-dot probe with 16 to 20 GHz real-time oscilloscopes and a 50 GHz sampling oscilloscope. Measured risetimes are down to ca. 50 ps, and the dependence of voltage collapse on gas density and electric field between the electrodes is reported. Integrity of data is analyzed and experimental results are compared with present theory found in literature and previous results measured with alternative real-time systems.
16
Content available remote

Microbial Inactivation by Electric Discharge with Metallic Grid

70%
Scholtz V., Kvasničková E., Julák J.
Acta Physica Polonica A
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2013
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vol. 124
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issue 1
62-65
EN
The area of microbial inactivation by the low-temperature plasma produced by DC electric cometary discharge is increased by insertion of an electrically insulated metallic grid between the discharge and the target object. Gram-negative bacteria are almost fully inactivated; an additional zone of incomplete inactivation appears for Gram-positive bacteria and yeasts.
17
Content available remote

Location and Identification of Acoustic Signals Recorded in Power Oil Transformers within the Band of 20-180~kHz

70%
Olszewska A., Witos F.
Acta Physica Polonica A
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2011
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vol. 120
|
issue 4
709-712
EN
Emission acoustic signals, recorded in investigated power oil transformers, have been analyzed in the time, frequency and time-frequency domain. Analysis of each signal has been started by filtration within selected frequency band and subsequently the following quantities have been calculated: spectral power density, phase-time characteristic, averaging phase-time characteristic, short-time Fourier transform spectrograms, signal amplitude distributions, descriptors with acronyms ADC and ADP and thereafter maps of descriptors on lateral walls of transformers can be carried out. Frequency bands applied in order to filtration have been chosen in such a way so that signals coming from different sources (among other things from partial discharges, Barkhausen's effect, oil circulation and outer acoustic disturbances) can be differentiated. The sources have been localized using maps of descriptors calculated for selected frequency bands. The fundamental properties of obtained signals have been determined. Such properties describe: partial discharges, Barkhausen's acoustic effect and other acoustic interferences.
18
Content available remote

Analysis of Properties Characteristic for Acoustic Emission Signals Recorded On-Line in Power Oil Transformers

70%
Witos F., Olszewska A., Szerszeń G.
Acta Physica Polonica A
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2011
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vol. 120
|
issue 4
759-762
EN
Investigation results of properties characteristic for acoustic emission signals recorded in two selected power oil transformers are presented. Signals were put to the filtration, whereas components coming from partial discharges have been left. The calculations concerned: phase-time characteristics, averaging phase characteristics, averaging short time Fourier transform spectrograms, amplitude distributions of signals, values of acoustic emission descriptor with acronym ADC. On the ground of calculated basic characteristics and maps of ADC descriptor three areas have been selected on lateral walls of transformer tanks. Acoustic emission signals recorded in these areas were analyzed from the point of view how is influence of propagation path on these properties.
19
Content available remote

Location of Partial Discharge Sources and Analysis of Signals in Chosen Power Oil Transformers by Means of Acoustic Emission Method

70%
Olszewska A., Witos F.
Acta Physica Polonica A
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2012
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vol. 122
|
issue 5
921-926
EN
The original system useful for analysis of signals recorded during investigations of partial discharges within power oil transformers by means of acoustic method is presented. This method includes the basic and advanced analysis of recorded data. In the frame of basic analysis of data recorded signals undergo filtration in chosen frequency bands and next the analysis is made - in domain of time, frequency, time-frequency and discrimination threshold. In the frame of advanced analysis of data the amplitude distributions of acoustic emission signals and the acoustic emission descriptors (defined by the authors) are calculated in order to outline maps of acoustic emission descriptors on lateral walls of a transformer; it is a base for location of sources of partial discharges by means of the original method consisted in determination of advance degree of a signal. Results of this analysis, for signals recorded in two chosen transformers with identical construction (partial discharge occurred only within one of them), are presented in the paper. The source of partial discharge, situated within oil near transformer tank, was localized; the revision confirmed this result. Properties of recorded emission acoustic signals at chosen measuring points situated on the tank, in function of distance between the partial discharge source and measuring points, are presented.
20
Content available remote

Identification of Deformation Processes within Power Oil Transformers Using Maps of ADC Descriptors in Selected Frequency Bands

61%
Olszewska A.
Acta Physica Polonica A
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2013
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vol. 124
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issue 3
525-528
EN
The paper presents identification results of deformation processes within power oil transformers where - according to dissolved gas analysis investigation results - partial discharges took place. The original method worked out for analysis of acoustic emission signals recorded within tested transformer and particularly maps of ADC descriptors have been applied. Analysis has been carried out within chosen frequency bands in order to distinguish signals coming from different sources (among other things partial discharges, Barkhausen's effect, circulation of the oil, and outer acoustic sources). One source of partial discharges has been identified within the tested transformer as a result of analysis of acoustic emission signals.
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