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ОРЧЕСТВА
GAS DISCHARGE BREAKDOWN: WHAT IS IT AND METHODS OF DETERMINATION
Гущин Иван Олегович, Харлашина Софья Вячеславовна, Сибирский государственный университет науки и технологий имени М. Ф. Решетнева, г. Красноярск
E-mail: kharlashina. v@mail.ru
Abstract. In this paper, the nature and definition of an arc discharge are considered. The authors present the main groups of methods for detecting arc formation implemented in various fields.
Key words: electric arc, sparking, short circuit current.
An arc discharge is an electrical phenomenon in which an insulation breakdown occurs between two electrodes in a gaseous medium, which results in the formation of a plasma consisting of ionized gas particles. An arc discharge under the influence of an electric field occurs between the electrodes and has its own unique characteristics.
Detection, that is, the detection of arc formation is a complex process that requires a large number of calculations. In the field of arc formation detection, three groups of methods can be distinguished today, implemented:
- in the time domain (undemanding to computing power, gives a large number of false positives);
- in the frequency domain (requires complex calculations, widely researched, most often used);
- with the help of artificial intelligence and fuzzy logic (very complex algorithm, no developed techniques, poorly studied).
With an increase in the discharge current, a transition from a glow discharge to an arc discharge occurs. As the current increases, the cathode heating becomes strong, while due to the natural heterogeneity of the cathode surface and various cooling conditions of its sections, one of the sections heats up more than the others and begins to emit electrons by the mechanism of thermoelectronic emission. An increase in emissions leads to the formation of an intense local avalanche and to an increase in the number of ions bombarding this site. As a result, the discharge is contracted at the cathode into a spot of very small size, called the cathode spot, and the predominant emission mechanism becomes thermionic emission. As in a glow discharge, in an arc
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discharge there is a cathode potential drop area directly in front of the cathode. The width of this section is commensurate with the average free path of the electron. The magnitude of the cathode potential drop in an arc discharge is much smaller than in a glow discharge, it is close to the ionization potential of the gas with which the device is filled. The possibility of a gorenje discharge at such a low cathode voltage is due to the fact that, firstly, a decrease in the length of the cathode drop area helps to maintain a significant drop in potential near the cathode and, secondly, to maintain a high spot temperature, it is not the energy of each ion individually that is important, but the total energy of all ions coming to the cathode. The energy density turns out to be large, since the arc discharge current is large.
The arc discharge column is similar to the glow discharge column. The quantitative differences are due to the fact that the current density in the arc is much higher than in the glow discharge. In the anode region, depending on the size, shape, material of the anode, etc., both a slight increase in potential and its decrease can be observed. The gorenje voltage of an arc discharge consists of the cathode voltage, the voltage drop in the column and the anode potential drop, in general, this value is much less than for a glow discharge. In addition to thermoelectronic emission, electrostatic emission is observed in arc discharges. The formation of a strong electric field near the cathode is facilitated by intensive evaporation of the cathode material, which creates a high vapor pressure directly near it. At the same time, the average length of the electron path, and therefore the length of the cathode potential drop section, decreases to values of the order of 10-7 m, which, with cathode voltage values of the order of 10-20 volts, gives an average field strength in the cathode section of about 108 V/m. This is confirmed by the fact that in a mercury arc discharge, the luminous cathode spot is not the glow of the mercury surface, but the glow of gas above the mercury surface [1]. The temperature of mercury directly under the spot does not exceed 200 ° C. Thermionic emission cannot create a current of significant magnitude, because the field strength near the cathode is about 106 V/m. It is natural to assume that a high current density in the discharge is obtained due to electrostatic emission. Thermal ionization of the gas in the volume and emission of positive ions from the cathode probably also plays a role.
A feature of arc discharges is the high temperature of the gas and electrodes, amounting to several thousand degrees Kelvin, and the high intensity of the radiation of the discharge zone. Therefore, arc discharge is widely used for welding and cutting metals, as a source of radiation, etc. Another area of application of arc discharge is plasma-arc coating in mass production conditions in cases where there are no high requirements for the purity of the process. Examples here include the application of hardening coatings on metalworking tools and decorative coatings on consumer goods [2].
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Arc discharge is widely used in various industries. In industry, it is used for welding and cutting metals, creating lasers, manufacturing semiconductor devices and electrolysis. In the energy sector, arc discharge is used in electric arc furnaces for melting metals and generating electricity. Arc discharge is also used in lighting installations, including incandescent and gas-discharge lamp. Special equipment and compliance with safety measures are required to work with arc discharge. One of the most common techniques for working with arc discharge is welding. Welding machines are used for welding, which create an arc discharge between the welding electrode and the processed material. At the same time, protective media, such as inert gases or coatings, must be used to prevent oxidation of the weld [3].
Among the problems associated with arc discharge, the occurrence of noise can be distinguished. Random voltage or current fluctuations are observed at the terminals of electronic devices and systems. This noise is generated as a result of the random behavior of charge carriers inside the electronic components of the systems. The difficulty lies in the fact that arc detection devices can falsely trigger, mistaking the resulting noise for an arc discharge [4]. For this reason, the problem of arc detection and its differences from non-arc is relevant today.
Литература:
1. Брон О.Б. Электрическая дуга в аппаратах управления. - Л., Госэнергоиздат, 1954.
2. Таев И.С. Электрическая дуга в аппаратах низкого напряжения. - М., «Энергия», 1965.
3. ГОСТ 17703-72. Аппараты электрические коммутационные. Основные понятия. Термины и определения.
4. Xiu Yao, Luis Herrera, Yi Huang, and Jin Wang. The Detection of DC Arc Fault: Experimental Study and Fault Recognition. Department of Electrical and Computer Engineering, 2012.
