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Number of results: 16
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Abstract

The main purpose of the presented research is to investigate the partial discharge (PD) phenomenon variability under long-term AC voltage with particular consideration of the selected physical quantities changes while measured and registered by the acoustic emission method (AE). During the research a PD model source generating surface discharges is immersed in the brand new insulation mineral oil. Acoustic signals generated by the continuously occurred PDs within 168 hours are registered. Several qualitative and quantitative indicators are assigned to describe the PD variability in time. Furthermore, some longterm characteristics of the applied PD model source in mineral oil, are also presented according to acoustic signals emitted by the PD. Finally, various statistical tools are applied for the results analysis and presentation. Despite there are numerous contemporary research papers dealing with long-term PD analysis, such complementary and multiparametric approach has not been presented so far, regarding the presented research. According to the presented research from among all assigned indicators there are discriminated descriptors that could depend on PD long-term duration. On the grounds of the regression models analysis there are discovered trends that potentially allow to apply the results for modeling of the PD variability in time using the acoustic emission method. Subsequently such an approach may potentially support the development and extend the abilities of the diagnostic tools and maintenance policy in electrical power industry.
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Abstract

The paper analyses the possibilities of treating the ignition cable in the internal combustion engine as a distributed parameter system. It presents the experimental verification of computer simulations of signal propagation generated by ignition systems in the ignition cables, modelled by the distributed parameter system. The tests conducted to determine the wave parameters of ignition cables, as well as the results of numerical simulations and their experimental verifications, are presented. It is concluded that the modelling of the ignition cable by means of a long line gives positive results that can be used for the design of a spark plug with impedance equal to wave impedance of the ignition cable.
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Abstract

Studies of a snow cover on the Waldemar Glacier have been carried out during three spring seasons. In spite of its small area, there is considerable spatial variation in snow deposition on the Waldemar Glacier, different during successive seasons. Winter snow accumulation was the highest in 1995/96 (75 cm in water equivalent), but almost similar in 1996/97 and 1997/98, equal to 48 cm and 42 cm w.e., respectively. Snow cover shows specific physico-chemical features, with many sorts of snow different in its structure, hardness, density and moistening. All analysed snow profiles comprised layers of different grain size and hardness. Volume of water trapped in naledies was estimated to about 457,000 m3 in May 1998. The average winter runoff from the glacier was estimated to 0.024 m3/s i.e. about 91/s.km2.
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Abstract

An acoustic emission method (AE) is widespread and often applied for partial discharge (PD) diagnostics, mainly due to its ease of application as well as noninvasiveness and relatively high sensitivity. This paper presents comparative analysis of AE signals measurement results archived under laboratory conditions as well as on-site actual AE signals generated by inside PDs in electrical power transformer during its normal service. Three different PD model sources are applied for laboratory research: point to point, multipoint to plate and surface type. A typical measuring set up commonly used for on-site transformer PD diagnostics is provided for the laboratory tasks: piezoelectric joint transducer, preamplifier, amplifier and measuring PC interface. During the on-site research there are three measuring tracks applied simultaneously. Time domain, time-frequency domain and statistical tools are used for registered AE signals analysis. A number of descriptors are proposed as a result of the analysis. In the paper, at- tempt of AE signals descriptors, archived under laboratory condition application possibilities for on-site PD diagnostics of power transformers during normal service is made.
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Abstract

Biocompatible coatings produced on the basis of the chemically extracted natural hydroxyapatite (HAp) from the animal bones were deposited using multiplex method comprising glow discharge nitriding (GDN) of the titanium alloy substrate and pulsed laser deposition (PLD) of HAp on the formerly fabricated titanium nitride layer (TiN). The TiN interlayer plays an important role improving adhesion of HAp to substrate and preserves the direct contact of the tissue with metallic substrate in the case of possible cracking of HAp coating. Surface morphology of deposited layers, crystallographic texture and residual stress were studied in relation to the type of laser applied to ablation (Nd:YAG or ArF excimer), laser repetition, temperature of substrate and atmosphere in the reactive chamber.
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Abstract

An alternative method for analysis of acoustic emission (AE) signals generated by partial discharges (PD), based on a correlation between voltage phase run and AE pulses, so called phase resolved PD pattern (PRPD), is presented in the paper. PRPD pattern is a well-known analysis tool commonly used in such PD diagnostic methods as conventional electrical and UHF ones. Moreover, it yields various signal analysis abilities and allows a direct correlation indication between measurement results achieved using different methods. An original PRPD measurement methodology applied for AE method as well as some exemplary measurement results and further data analysis capabilities are presented in the paper. Also a comparative analysis of PRPD patterns achieved using various measurement methods and different PD source configurations have been investigated. All presented experiments were done under laboratory conditions using PD model sources immersed in the insulation oil. The main purpose of the presented research is to indicate an all-embracing analytical tool that yields an ability to direct comparison (qualitative as well as quantitative) of the AE measurement results with other commonly applied PD measurement methods. The presented results give a solid fundamental for further research work concerning a direct correlation method for AE and other described in the paper diagnostic techniques, mainly in order to continue PD phenomena analysis and assessment in real life high voltage apparatus insulation systems under normal onsite operation conditions.
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Abstract

Although the gas insulated structures have a high degree of reliability, the unavoidable defects are primary reason of their failures. Partial discharge (PD) has been regarded as an effective indication for condition monitoring and diagnosis of gas insulated switchgears (GISs) to ensure their reliable and stable operation. Among various PD detection methods, the ultra-high frequency (UHF) technique has the advantages of on-line motoring and defect classification. In this paper, there are presented 7 types of artificial electrode systems fabricated for simulation of real insulation defects in gas insulated structures. A real-time measurement system was developed to acquire defect patterns in a form of phase-resolve partial discharge (PRPD) intensity graph, using a UHF sensor. Further, the discharge distribution and statistical characteristics were extracted for defect identification using a neural network algorithm. In addition, a conversion experiment was proposed by detecting the PD pulse simultaneously using a non-induction resistor and a UHF sensor. A relationship between the magnitude of UHF signal and the amplitude of apparent charge was established, which was used for evaluation of PD using the UHF sensor.
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Abstract

The results from a hydrological monitoring program of Breelva basin (Spitsbergen, Svalbard) have been analysed to improve the understanding of the Werenskiöld Glacier system’s functioning in the High Arctic. Hydrographs of a 44 km 2 river basin (27 km 2 of which was covered by a glacier) were analysed for the period 2007–2012. Seasonal discharge fluctuations were linked to glacier ablation and meteorological parameters, including atmospheric circulation types. A dichotomy was found in the discharge peaks generation during the hydrologically active season, with the main role played by snow and ice melt events during its first part and the rainfall regime dominating its second part. Foehn type strong winds played a significant role in the generation of ablation type floods ( e.g. in August 2011). A simple classification of the runoff regime was applied to the examined six−year period, resulting in the identification of its three types: the ablation type (dominant in 2007 and 2009), the rainfall type (in the years 2011–2012), and the mixed type (during 2008 and 2010). According to publications the river flow season in Spitsbergen begins in June and end with freeze−up in September or at the beginning of October. Recently, this season for Breelva tend to be extended with the mid−May onset and end in the second part of October. A multiannual trend was noted that reflects a growing importance of rainfalls, especially in September. Rainfall waters play a more distinct role in outflow from the Breelva catchment recently.
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Abstract

The data set of the Warta discharges in Poznań (Poland) is one of the largest in the world as the daily observations of river stages have been conducted without interruptions since January, 1st, 1822. The Poznań measurement profile is situated in the 243.6 km and closes the catchment area of approximately 25 thousand square kilometers. The data used as the input in the paper were daily values of the Warta discharges in Poznań in the years 1822-2012. The climate in Poznań, a city situated in the centre of the Wielkopolska (Greater Poland) region, is relatively stable (Miler et al. 2005). Also the Warta River runoff shows considerable stability, especially in terms of mean annual values. Short-term trends are random in character. It was found that the Jeziorsko reservoir (total storage volume of 203 000 000 m3, officially put to use on September, 9th, 1987) significantly reduced daily variability of the flows and reduced peak discharge of the flood wave in the summer of 1997 on the Warta River at Poznań. The calculated periodogram for mean annual discharges of the Warta River in Poznań shows that there are main periodicities of ca. 10 year lengths. The research of the Provincial Inspectorate for Environmental Protection (WIOŚ) in Poznań shows a gradual improvement of water quality in the Warta River in Poznań.
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Abstract

The loss of power and voltage can affect distribution networks that have a significant number of distributed power resources and electric vehicles. The present study focuses on a hybrid method to model multi-objective coordination optimisation problems for dis- tributed power generation and charging and discharging of electric vehicles in a distribution system. An improved simulated annealing based particle swarm optimisation (SAPSO) algorithm is employed to solve the proposed multi-objective optimisation problem with two objective functions including the minimal power loss index and minimal voltage deviation index. The proposed method is simulated on IEEE 33-node distribution systems and IEEE-118 nodes large scale distribution systems to demonstrate the performance and effectiveness of the technique. The simulation results indicate that the power loss and node voltage deviation are significantly reduced via the coordination optimisation of the power of distributed generations and charging and discharging power of electric vehicles.With the methodology supposed in this paper, thousands of EVs can be accessed to the distribution network in a slow charging mode.
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Abstract

A computer measurement system, designed and built by authors, dedicated to location and description of partial discharges (PD) in oil power transformers examined by means of the acoustic emission (AE) method is presented. The measurement system is equipped with 8 measurement channels and ensures: monitoring of signals, registration of data in real time within a band of 25–1000 kHz in laboratory and real conditions, basic and advanced analysis of recorded signals. The basic analysis carried out in the time, frequency and time-frequency domains deals with general properties of the AE signals coming from PDs. The advanced analysis, performed in the discrimination threshold domain, results in identification of signals coming from different acoustic sources as well as location of these sources in the examined transformers in terms of defined by authors descriptors and maps of these descriptors on the side walls of the tested transformer tank. Examples of typical results of laboratory tests carried out with the use of the built-in measurement system are presented.
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Abstract

The analyzed heat accumulator is a key element in a hybrid heating system. In this paper, analytical and numerical models of the ceramic heat accumulator are presented.The accuracy of finite difference methods will be assessed by comparing the results with those obtained from the exact analytical solution.
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Abstract

Electrical Discharge Machining (EDM) process with copper tool electrode is used to investigate the machining characteristics of AISI D2 tool steel material. The multi-wall carbon nanotube is mixed with dielectric fluids and its end characteristics like surface roughness, fractal dimension and metal removal rate (MRR) are analysed. In this EDM process, regression model is developed to predict surface roughness. The collection of experimental data is by using L9 Orthogonal Array. This study investigates the optimization of EDM machining parameters for AISI D2 Tool steel using Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method. Analysis of variance (ANOVA) and F-test are used to check the validity of the regression model and to determine the significant parameter affecting the surface roughness. Atomic Force Microscope (AFM) is used to capture the machined image at micro size and using spectroscopy software the surface roughness and fractal dimensions are analysed. Later, the parameters are optimized using MINITAB 15 software, and regression equation is compared with the actual measurements of machining process parameters. The developed mathematical model is further coupled with Genetic Algorithm (GA) to determine the optimum conditions leading to the minimum surface roughness value of the workpiece.
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