Wrocław University of Science and Technology
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431 research outputs found
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Inefficacité des Paratonnerres à Avance d’Amorçage
Full text linkTests on three early streamer emission (ESE) terminals, manufactured by different firms, were carried out. The main measure criterion was the breakdown voltage of the air gap consisted of the high voltage electrode (rod or plate) and a grounded ESE terminal. Additionally, the time to breakdown was estimated from the oscillograms. The breakdown voltage was measured at standard switching impulses or under lightning impulses of both polarities or under AC voltage. The used distance ranged from 5 cm up to 4 m and voltage magnitude from 30 kV up to 2.5 MV. Except only one ESE terminal showing an advantage at an air gap of a few centimetres under AC voltage, these careful measurements show that the air gaps with ESE terminals have the same breakdown voltages as the air gaps with Franklin rods. Therefore, the large protection zone of ESE terminals, as claimed by their manufactures, is practically impossible
Thermische Eigenshaften von Fremdschichten
No full textIn the paper the conductive behavior of saturated and unsaturated electrolytic solutions as a function of temperature is discussed. The influence of solutions of NaCl, H2SO4, CaO and CaSO4 on the pollution flashover voltageand the leakage current for a flat model of an insulator (glass plate) was studied. The obtained pollution characteristics are compared to each other depending on the electrolyte type used to obtain the conductive layer as well as depending on the pollution paprameter (ESDD or Ks). The results show, that may be big differences in the behavior of artificial and natural pollution layers
LONG-TERM STUDY OF CHANGES OF PHYSICO-CHEMICAL PARAMETERS OF TRANSFORMER OILS
Full text linkThe average age of transformers in service is increasing and approaching the end of design life. Hence there is an increasing need to assess the condition of transformers. The utilities currently use a number of diagnostic techniques to assess the insulation condition of aged transformers. Among them physic-chemical analysis of transformer oil are frequently used. The article presents the results of many years of routine laboratory testing of oil transformers operated in the EnergiaPro energy company. Oil testing included measurements of total acidity, water content, breakdown voltage, resistivity, tgδ
Piorunochrony pseudoaktywne
Full text linkOpisano własności podstawowych form wyładowań elektrycznych w powietrzu: strimera i lidera. Wykazano, że strefa ochronna piorunochronów ESE z wczesną emisją strimera nie może być większa od strefy ochronnej klasycznych piorunochronów Franklina. The paper describes basic properties of two main types of electrical discharges in atmospheric air: streamer and leader. It was shown that the protection zone of Early Streamer Emission terminals can not be greater than the protection zone of classical Franklin terminals. (Active lightning terminals)
EMI Shielding using Composite Materials with Plasma Layers
Full text linkElectromagnetic compatibility (EMC), including the engineering of materials used for shielding,, is currently one of the most extensively developing field of applications of composite materials (Bula et al., 2006; Jaroszewski & Ziaja, 2010; Koprowska et al., 2004, 2008; Sarto et al. 2003, 2005; Wei et al., 2006; Ziaja et al., 2008, 2009, 2010). The development of lightweight, mechanically resistant, shielding materials is possible by using plasma technology. Due to rapid increase in the number of sources generating the electromagnetic (EM) fields, e.g. radio broadcasting, television, radio communication, cellular networks, continuously extending range of applied frequencies, and increasing power generated by PEM sources, the shielding design is getting more and more challenging. These challenges stem from the fact that complex EM power engineering systems are built of miniaturized electronic circuits. The progressing miniaturization reduces the resistance of the electronic circuits to electromagnetic exposure. Therefore, the choice of suitable materials for the shields and their appropriate arrangement has an essential meaning
Leakage currents on naturally contaminated porcelain and silicone insulators.
Full text linkThe leakage current measurements on standard post insulators and on rod insulators without sheds were carried out. The porcelain and silicone rubber insulators were tested at Glogow station under the voltage of 75 kV. It was shown that the currents on porcelain insulators are sometimes greater than the currents on silicone insulators. However, the currents on both insulator types are often similar. Silicone rubber insulators are more contaminated than porcelain insulators. The current analysis has been made using the static theory of pollution flashover
Pollution flashover of long rod insulators with different profiles.
Full text linkPollution test of four long rod insulators with different shapes were carried out according to flow on, salt fog and solid layer methods. The following porcelain insulators were investigated: a standard type insulator VKL75/14 with 14 sheds, an insulator with 15 stepped sheds LPZS 75/15, an insulator with alternating sheds LPZ 75/37W, and a screw type insulator LPS 75/11. During tests the flashover voltage, leakage currents, layer conductivity, salinity of water spray or salt deposit density were measured. The discharge activity and dry band pattern on insulators were observed. The flashover voltage (FOV) of insulator with stepped sheds according to salt fog and solid layer method was higher than the FOV of insulator with alternating sheds in spite that the leakage distance of insulator LPZ75/37W was longer. On the other hands the FOV of screw insulator was lowest due to the formation of single dry band at the upper flange
Influence of moisture and partial discharges on the degradation of high-voltage surge arresters.
Full text linkThis paper reports the influence of moisture and internal partial discharges on the degradation of metal oxide varistors in high-voltage surge arresters. Both factors cause an increase in the varistor current under the operating voltage. This phenomenon is dangerous and can cause a total outage of the metal oxide arrester. In the field the moisture ingress can lead to internal discharges. Owing to recovery processes the changes in the voltage–current characteristics of varistors caused by moisture or partial discharges decrease in dry and partial discharge free conditions. The interesting behaviour of some varistors which were degraded by partial discharges was observed
Application of lightning location systems for fault detection on transmission and distribution lines
Full text linkThe lightning location systems were installed in many countries during last twenty years. The paper presents the SAFIR system called PERUN, which was built in Poland in 2002. The lightning location systems are used for different purposes including among other things meteorology, weather forecasting and aviation. A brief review of fault detection on transmission and distribution lines made abroad and the first experience of the Polish National Grid PSE was shown