Wrocław University of Science and Technology
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Mechanical-Acoustic Examination of Ceramic Material
Get PDFThe paper presents a new mechanical-acoustic method of research of material degradation. As comparative method there was used microscopic technique (MO). Examinations were carried out on the samples of C 130 kind porcelain cut out from the rod of typical HV line insulator LP 75/31W. On the basis of acoustic emission (AE) measurements of slowly compressed samples, the successive stages of structural degradation have been registered
Electro-physical properties of PTFE/bronze composites
No full textElectret state of polymer/metal composite based on polytetrafluornthylene (PTFE) and bronze powder was investigated.It was found that bronze/PTFE composites have very long lifetime (2*10^12 s) of charge stored in the bulk - the same order of magnitude as the most stable polymeric electrets
Measurement of frozen-in polarization in polycarbonate films
No full textSpace charge accumulated in dielectric materials affect their properties. The electric strength is determinated by the presence of additional electric field resulting from space charge accumulated near electrodes f11. Space charge phenomena in dielectric materials have been widely discussed recently and there are many experimental techniques for measuring space charge and electric field distribution in solid dielectrics [2-3]. The thermal methods, pressure wave propagation and electroacoustic methods are commonly used for characterization of electrical state of charged materials such as electret, electrical insulation, antistatic materials and functional polymers [4. 5]. The above methods give the same information on the electrical State of material [6]. If is usually the information tin linear combination of real and polarizational charges. Electret properties originate from real surface charges and space charges distributed in the bulk as well as from dipole polarization. The similarity between real charges and ends of dipoles makes it difficult to distinguish between (hem. The problem of discrimination between polarization and real charges was discussed in literature [7, 81. In this work the step electroacoustic method (SEA) was applied for measurement of electrical field distribution along the sample thickness [91, The SEA signals were measured simultaneously during thermally stimulated discharge (TSD) of the sample. The recorded thermogram of current density j tsd gives additional information on discriminating the kind of charges. Simultaneous measurement of TSD and space charge distribution allows to get admiration on local components of the TSD current in a dielectric as it was shown in [10]. In this work simultaneous measurements of electric field using SEA method and TSD currents were used for discriminating between real and frozen-in polarization charges in polycarbonate films after corona charging at higher temperatures
Verschmutzungsverhalten von Hochspannungsisolatoren und Ableitern
Get PDFVon 1980 bis 2005 wurde das Verschmutzungsverhalten unterschiedlicher Hochspannungsisolatoren und Überspannungsableiter im Freiluftprüffeld „Glogów“ untersucht. Fortschritte im Umweltschutz und neue Technologien haben zu einer bedeutenden Abnahme der Staub- und Gasemissionen in der Nähe von Kupferhütten geführt. Als direkte Folge hat sich der Umweltverschmutzungsgrad des Gebiets von vier (sehr hoch) in den 1980er-Jahren auf eins (leicht) im Jahr 2003 reduziert. Die Überschlagspannung von Porzellanisolatoren wurde 1987 unter natürlichen Bedingungen und in den Jahren 2002 bis 2004 nach Befeuchtung mit Spritzwasser gemessen. Ferner wurden die Spannungsfestigkeit von Keramikisolatoren mit der von silikon- bzw. PTFE-beschichteten Isolatoren verglichen und die Messwerte der Innentemperatur von Metalloxid-Überspannungsableitern in einem Keramikgehäuse dargestellt
Voltage Disturbances Standard EN 50160 - Voltage Characteristics in Public Distribution Systems
Get PDFElectrical energy is a product and, like any other product, should satisfy the proper quality requirements. If electrical equipment is to operate correctly, it requires electrical energy to be supplied at a voltage that is within a specified range around the rated value. A significant part of the equipment in use today, especially electronic and computer devices, requires good power quality (PQ). However, the same equipment often causes distortion of the voltage supply in the installation, because of its non-linear characteristics, i.e. it draws a non-sinusoidal current with a sinusoidal supply voltage (see Section 3.1 of this Guide). Thus, maintaining satisfactory PQ is a joint responsibility for the supplier and the electricity user. According to standard EN 50160 [1] the supplier is the party who provides electricity via a public distribution system, and the user or customer is the purchaser of electricity from a supplier. The user is entitled to receive a suitable quality of power from the supplier. In practice the level of PQ is a compromise between user and supplier. Where the available PQ is not sufficient for the user’s needs, PQ improvement measures will be needed and will be the subject of a cost-benefit analysis (see Section 2.5 of this Guide). However, the cost of poor PQ usually exceeds the cost of measures required for improvement - it is estimated that losses caused by poor power quality cost EU industry and commerce about € 10 billion per annum (see Section 2.1 of this Guide). However, electrical energy is a very specific product. The possibility for storing electricity in any significant quantity is very limited so it is consumed at the instant it is generated. Measurement and evaluation of the quality of the supplied power has to be made at the instant of its consumption. The measurement of PQ is complex, since the supplier and user, whose sensitive electrical equipment is also a source of disturbances, have different perspectives. Standard IEC 038 [2] distinguishes two different voltages in electrical networks and installations: supply voltage, which is the line-to-line or line-to-neutral voltage at the point of common coupling, i.e. main supplying point of installation, utility voltage, which is the line-to-line or line-to-neutral voltage at the plug or terminal of the electrical device. The main document dealing with requirements concerning the supplier’s side is standard EN 50160, which characterises voltage parameters of electrical energy in public distribution systems. This is a European standard but it is supplemented in some regions or countries by other supplemental standards, such as [3] in Germany, or [4] in Poland. Many regional codes, such as the German TAB [3] apply to an individual utility, but these are being unified as part of the liberalisation of the German electricity market. According to IEC 038, both standard EN 50160 and rules [3,4] concern the supply voltage, i.e. that measured at the point of common coupling. On the user’s side, it is the quality of power available to the user’s equipment that is important. Correct equipment operation requires the level of electromagnetic influence on equipment to be maintained below certain limits. Equipment is influenced by disturbances on the supply and by other equipment in the installation, as well as itself influencing the supply. These problems are summarised in the EN 61000 series of EMC standards, in which limits of conducted disturbances are characterised. Equipment sensitivity to utility voltage quality, as well as mitigation measures, are presented in Section 3 (Harmonics) and Section 5 (Voltage Disturbances) of this Guide. The subject of this section is a detailed presentation of standard EN 50160 and an analysis of its requirements according to the operation of chosen equipment. Methods of measuring supply voltage parameters are also presented
How to Reduce Errors of Distance Fault Locating Algorithms
Get PDFDistance fault locating digital algorithms are often based on the processing of fundamental components which are contained in the currents and Voltages. If the extraction of these components is done by means of correlating the signals with sine/cosine functions of the fundamental frequency, and the data window is shorter then one period, the presence of aperiodic components in the signals gives rise to large errors. The paper suggests, that to reduce the errors the signals ought to be correlated with sine/cosine functions which have periods equal to the data window length
Transverse Interference Voltages on Secondary Protection Wiring at Substations
No full textThis paper presents simple equivalent circuits which enables calculation of expected values of transverse interference voltages on various secondary circuits at Substations. The transverse voltages appear only if there is an asymmetry in secondary circuits. They may cause damages of insulation or maloperation of protective devices. On the basis of the equivalent circuits, the efficiency of means which may be adopted for suppressing the transverse voltages are discussed
Hygroscopic Properties of Pollutants on HV Insulators
Get PDFThe mechanism of moisture absorption by an insulator surface contaminated with different salts was described. A list of some salts depending on their hygroscopicity was given. Measurements of surface conductivity and leakage current on flat insulator models at different relative humidities and with different types of salt were carried out. At natural atmospheric conditions the flashover voltage of cap and pin insulators subjected to 250/2500 ps switching impulses was evaluated
Behaviour of Zinc Oxide Surge Arresters Under Pollution
Get PDFThis paper presents results of pollution tests with A.C. voltages which were carried out with a multi - unit zinc oxide arrester . The interaction between the polluted porcelain housing and the inner varistor column due to capacitive coupling has been found to be responsible for the temperature rise of varistor elements. The different voltage distribution between inside and outside of the arrester also causes a high radial electric field which can lead to internal discharges if the radial insulation system is not properly designed. These internal discharges may damage varistor elements which are not adequately coated and may cause a total destruction of the arrester . The shape of the internal and external currents due to discharges is analysed. A test method to compare different arrester constructions under severe pollution is proposed. The method can also be applied to demonstrate the absence of discharges for a certain arrester design under extreme conditions of pollution during type tests
Voltage Endurance Test of Vacuum Insulation for Cryocables
Get PDFVacuum insulation with cylindrical ceramic spacer insulators has been studied with respect to changes of its ac flashover voltage with time. The distributions of times to failure, which were found to confirm Weibull's distribution, were used for plotting the regression curves for times up to 350 h. The results show that even at rather low stresses the flashover voltage decreased in time. This phenomenon is connected with the recorded deposition of metal particles from the electrodes on the surface of the spacers during the tests. This possibility of the decrease of the flashover voltage, induced by the deconditioning effects of contaminating conducting particles generated under the working stress by the system itself, must be taken into account when considering the suitableness of using special means of increasing the short-time flashover voltage of vacuum insulation for cryocables