Arc discharge application in technology. Self-contained arc discharge (low, medium and high pressure)

Species gas discharge and their application. The concept of plasma.

Branch:

Accounting and rights

Speciality:

Jurisprudence

Group:

Compiled by:

Evtikhevich A. A.

Teacher:

Orlovskaya G.V.

2011
Content:

Page 1: Gas discharge

Application of gas discharge

Page 2:Spark discharge

Corona discharge

Page 3: Application of corona discharge

Page 4: Arc discharge

Page 5: Application of arc discharge

Glow discharge

Page 6-7: Plasma

Page 8: Literature

Gas discharge- a set of processes that occur when an electric current flows through a substance in a gaseous state. Typically, current flow becomes possible only after sufficient ionization of the gas and formation of plasma. Ionization occurs due to collisions of electrons accelerated in an electromagnetic field with gas atoms. In this case, an avalanche increase in the number of charged particles occurs, since during the ionization process new electrons are formed, which, after acceleration, also begin to participate in collisions with atoms, causing their ionization. For the occurrence and maintenance of a gas discharge, the existence of an electric field is required, since plasma can exist only if electrons acquire energy in an external field sufficient to ionize atoms, and the number of formed ions exceeds the number of recombined ions.

If additional ionization due to external sources is necessary for the existence of a gas discharge (for example, using ionizing radiation), then the gas discharge is called dependent(such discharges are used in Geiger counters).

To carry out a gas discharge, both time-constant and variable electric fields are used.

Depending on the conditions under which the formation of charge carriers occurs (gas pressure, voltage applied to the electrodes, shape and temperature of the electrodes), several types are distinguished independent categories: smoldering, spark, corona, arc.

Gas discharge applications

• Arc discharge for welding and lighting.
• Ultra high frequency discharge.
• Glow discharge as a light source in fluorescent lamps and plasma screens.
• Spark discharge for ignition of the working mixture in engines internal combustion.
• Corona discharge for cleaning gases from dust and other contaminants, for diagnosing the condition of structures.
• Plasmatrons for cutting and welding.
• Discharges for pumping lasers such as helium-neon laser, nitrogen laser, excimer lasers, etc.

• in a Geiger counter,
• in ionization vacuum gauges,
• in thyratrons,
• in krytrons,
• in a Heussler tube.

Spark discharge. Let's connect the ball electrodes to the battery of capacitors and start charging the capacitors using an electric machine. As the capacitors charge, the potential difference between the electrodes will increase, and consequently, the field strength in the gas will increase. As long as the field strength is low, no changes can be noticed in the gas. However, with sufficient field strength (about 30,000 V/cm), an electric spark appears between the electrodes, which looks like a brightly glowing winding channel connecting both electrodes. The gas near the spark heats up to high temperature and suddenly expands, causing sound waves, and we hear a characteristic crack. Capacitors in this setup are added to make the spark more powerful and therefore more effective.
The described form of gas discharge is called a spark discharge, or spark breakdown of a gas. When a spark discharge occurs, the gas suddenly, abruptly, loses its insulating properties and becomes a good conductor. The field strength at which gas spark breakdown occurs has different meaning for different gases and depends on their state (pressure, temperature). For a given voltage between the electrodes, the field strength is lower, the further the electrodes are from each other. Therefore, than longer distance between the electrodes, the greater the voltage between them is necessary for spark breakdown of the gas to occur. This voltage is called breakdown voltage. The occurrence of a breakdown is explained as follows. There is always a certain amount of ions and electrons in a gas, arising from random causes. Usually, however, their number is so small that the gas practically does not conduct electricity. At relatively low field strengths, such as we encounter when studying non-self-conductivity of gases, collisions of ions moving in an electric field with neutral gas molecules occur in the same way as collisions of elastic balls. With each collision, the moving particle transfers part of its kinetic energy to the resting one, and both particles scatter after the impact, but no internal changes does not happen in them. However, if the field strength is sufficient, the kinetic energy accumulated by the ion in the interval between two collisions can become sufficient to ionize the neutral molecule upon collision. As a result, a new negative electron and a positively charged residue - an ion - are formed. This ionization process is called impact ionization, and the work that needs to be expended to remove an electron from an atom is called ionization work. The amount of ionization work depends on the structure of the atom and is therefore different for different gases. Electrons and ions formed under the influence of impact ionization increase the number of charges in the gas, and in turn they come into motion under the influence of an electric field and can produce impact ionization of new atoms. Thus, this process “reinforces itself”, and ionization in the gas quickly reaches a very large value. All phenomena are quite similar to a snow avalanche in the mountains, for the occurrence of which an insignificant lump of snow is enough. Therefore, the described process was called an ion avalanche. The formation of an ion avalanche is the process of spark breakdown, and the minimum voltage at which an ion avalanche occurs is the breakdown voltage. We see that during a spark breakdown the reason for gas ionization is the destruction of atoms and molecules during collisions with ions. One of the natural representatives of a spark discharge is lightning - beautiful and not safe.
Corona discharge. The occurrence of an ion avalanche does not always lead to a spark, but can also cause a discharge of another type - a corona discharge. Let's stretch a metal wire AB with a diameter of a few tenths of a millimeter on two high insulating supports and connect it to the negative pole of a generator that provides a voltage of several thousand volts, for example, to a good electric machine. We will take the second pole of the generator to the Earth. We will get a kind of capacitor, the plates of which are our wire and the walls of the room, which, of course, communicate with the Earth. The field in this capacitor is very inhomogeneous, and its intensity is very high near a thin wire. By gradually increasing the voltage and observing the wire in the dark, you can notice that at a certain voltage, a faint glow (“corona”) appears near the wire, covering the wire on all sides; it is accompanied by a hissing sound and a slight crackling sound. If a sensitive galvanometer is connected between the wire and the source, then with the appearance of a glow, the galvanometer shows a noticeable current flowing from the generator through the wires to the wire and from it through the air of the room to the walls connected to the other pole of the generator. The current in the air between the wire AB and the walls is carried by ions formed in the air due to impact ionization. Thus, the glow of air and the appearance of current indicate strong ionization of air under the influence of an electric field. A corona discharge can occur not only at the wire, but also at the tip and in general at all electrodes, near which a very strong inhomogeneous field is formed.
Application of corona discharge
1) Electrical gas purification (electric precipitators). A vessel filled with smoke suddenly becomes completely transparent when sharp metal electrodes connected to an electrical machine are inserted into it. Inside the glass tube there are two electrodes: a metal cylinder and a thin metal wire hanging along its axis. The electrodes are connected to the electrical machine. If a stream of smoke (or dust) is blown through a tube and the machine is set in motion, then as soon as the voltage becomes sufficient to form a corona, the escaping stream of air will become completely clean and transparent, and all solid and liquid particles contained in the gas will be deposited on the electrodes.
The explanation of the experience is as follows. Once the wire's corona is ignited, the air inside the tube becomes highly ionized. Gas ions, colliding with dust particles, “stick” to the latter and charge them. Since there is a strong electric field inside the tube, charged particles move under the influence of the field to the electrodes, where they settle. The described phenomenon is currently finding technical application for the purification of industrial gases in large volumes from solid and liquid impurities.
2) Counters elementary particles. Corona discharge underlies the operation of extremely important physical devices: so-called counters of elementary particles (electrons, as well as other elementary particles that are formed during radioactive transformations). One type of counter (Geiger–Müller counter) is shown in Fig. 1.
It consists of a small metal cylinder A, equipped with a window, and a thin metal wire stretched along the axis of the cylinder and insulated from it. The meter is connected to a circuit containing a voltage source B of several thousand volts. The voltage is chosen so that it is only slightly less than the “critical” one, i.e., necessary to ignite the corona discharge inside the meter. When a fast-moving electron enters the counter, the latter ionizes the gas molecules inside the counter, causing the voltage required to ignite the corona to slightly decrease. A discharge occurs in the meter, and a weak short-term current appears in the circuit.
The current arising in the meter is so weak that it is difficult to detect with a conventional galvanometer. However, it can be made quite noticeable if a very large resistance R is introduced into the circuit and a sensitive electrometer E is connected in parallel to it. When a current I appears in the circuit, a voltage U is created at the ends of the resistance, equal to Ohm’s law U = IxR. If you choose a resistance value R very large (many millions of ohms), but significantly less than the resistance of the electrometer itself, then even a very weak current will cause a noticeable voltage. Therefore, every time a fast electron gets inside the counter, the electrometer leaf will give off.
Such counters make it possible to register not only fast electrons, but also, in general, any charged, rapidly moving particles capable of ionizing a gas through collisions. Modern counters easily detect the entry of even one particle into them and, therefore, make it possible to verify with complete reliability and very clear clarity that elementary particles really exist in nature.
Arc discharge. In 1802, V.V. Petrov established that if you attach two pieces of charcoal to the poles of a large electrolytic battery and, bringing the coals into contact, slightly separate them, a bright flame will form between the ends of the coals, and the ends of the coals themselves will become white hot. Emitting a blinding light (electric arc). This phenomenon was independently observed seven years later by the English chemist Davy, who proposed calling this arc “voltaic” in honor of Volta.
Typically, the lighting network is powered by alternating current. The arc, however, burns more steadily if a constant current is passed through it, so that one of its electrodes is always positive (anode) and the other negative (cathode). Between the electrodes there is a column of hot gas that conducts electricity well. In normal arcs, this pillar emits significantly less light than hot coals. Positive coal, having a higher temperature, burns faster than negative coal. Due to the strong sublimation of coal, a depression is formed on it - a positive crater, which is the hottest part of the electrodes. Temperature of the crater in the air at atmospheric pressure reaches 4000 °C.
The arc can also burn between metal electrodes (iron, copper, etc.). In this case, the electrodes melt and quickly evaporate, which consumes a lot of heat. Therefore, the crater temperature of a metal electrode is usually lower than that of a carbon electrode (2000-2500 °C).
By forcing an arc to burn between carbon electrodes in compressed gas (about 20 atm), it was possible to bring the temperature of the positive crater to 5900 °C, i.e., to the temperature of the surface of the Sun. Under this condition, coal melting was observed.
The column of gases and vapors through which the electric discharge occurs has an even higher temperature. The energetic bombardment of these gases and vapors by electrons and ions, driven by the electric field of the arc, brings the temperature of the gases in the column to 6000-7000 °. Therefore, in the arc column, almost all known substances melt and turn into steam, and many chemical reactions, which do not go with more low temperatures. It is not difficult, for example, to melt refractory porcelain sticks in an arc flame.
To maintain an arc discharge, a small voltage is needed: the arc burns well when the voltage at its electrodes is 40-45 V. The arc current is quite significant. So, for example, even in a small arc, a current of about 5 A flows, and in large arcs used in industry, the current reaches hundreds of amperes. This shows that the arc resistance is low; Consequently, a luminous gas column conducts electric current well.
Such strong ionization of the gas is possible only due to the fact that the arc cathode emits a lot of electrons, which, with their impacts, ionize the gas in the discharge space. Strong electron emission from the cathode is ensured by the fact that the arc cathode itself is heated to a very high temperature (from 2200° to 3500°C depending on the material). When, to ignite an arc, we first bring the coals into contact, then at the point of contact, which has a very high resistance, almost all the Joule heat of the current passing through the coals is released. Therefore, the ends of the coals become very hot, and this is enough for an arc to break out between them when they move apart. Subsequently, the cathode of the arc is maintained in a heated state by the current itself passing through the arc. Main role Bombardment of the cathode by incident particles plays a role in this positive ions.
Application of arc discharge
Due to the high temperature, the arc electrodes emit dazzling light, and therefore the electric arc is one of the best light sources. It consumes only about 0.3 watts per candle and is significantly more economical. Than the best incandescent lamps. Electric arc was first used for lighting by P. N. Yablochkov in 1875 and was called the “Russian light”, or “northern light”.
The electric arc is also used for welding metal parts (electric arc welding). Currently, the electric arc is very widely used in industrial electric furnaces. In global industry, about 90% of tool steel and almost all special steels are smelted in electric furnaces.
Of great interest is a mercury arc burning in a quartz tube, the so-called quartz lamp. In this lamp, the arc discharge occurs not in air, but in an atmosphere of mercury vapor, for which a small amount of mercury is introduced into the lamp, and the air is pumped out. The light of the mercury arc is extremely rich in invisible ultraviolet rays with strong chemical and physiological effects. Mercury lamps are widely used in the treatment of various diseases (“artificial mountain sun”), as well as in scientific research as a strong source of ultraviolet rays.
Glow discharge. In addition to the spark, corona and arc, there is another form of independent discharge in gases - the so-called glow discharge. To obtain this type of discharge, it is convenient to use a glass tube about half a meter long, containing two metal electrodes. Let's connect the electrodes to the source DC with a voltage of several thousand volts (an electric machine will do) and we will gradually pump out the air from the tube. At atmospheric pressure, the gas inside the tube remains dark because the applied voltage of several thousand volts is not enough to pierce the long gas gap. However, when the gas pressure drops sufficiently, a luminous discharge flashes in the tube. It looks like a thin cord (crimson in air, other colors in other gases) connecting both electrodes. In this state, the gas column conducts electricity well.
With further evacuation, the luminous cord blurs and expands, and the glow fills almost the entire tube. The following two parts of the discharge are distinguished: 1) the non-luminous part adjacent to the cathode, called the dark cathode space; 2) a luminous column of gas filling the rest of the tube, right up to the anode. This part of the discharge is called the positive column.
And this is how it works. During a glow discharge, gas conducts electricity well, which means that strong ionization is maintained in the gas all the time. In this case, unlike an arc discharge, the cathode remains cold all the time. Why does the formation of ions occur in this case?
The potential or voltage drop for each centimeter of length of the gas column in a glow discharge is very different in different parts discharge. It turns out that almost the entire drop in potential occurs in dark space. The potential difference that exists between the cathode and the space boundary closest to it is called the cathode potential drop. It is measured in hundreds, and in some cases thousands of volts. The entire discharge appears to exist due to this cathode fall.
The significance of the cathode fall is that positive ions, running through this large potential difference, acquire greater speed. Since the cathode drop is concentrated in thin layer gas, then almost no collisions of ions with gas atoms occur here, and therefore, passing through the region of cathode incidence, the ions acquire very high kinetic energy. As a result, when they collide with the cathode, they knock out a certain number of electrons from it, which begin to move towards the anode. Passing through dark space, electrons, in turn, are accelerated by the cathode potential drop and, when colliding with gas atoms in a more distant part of the discharge, produce impact ionization. The positive ions that arise in this case are again accelerated by the cathode fall and knock out new electrons from the cathode, etc. Thus, everything is repeated as long as there is voltage on the electrodes.
This means we see that the reasons for gas ionization in a glow discharge are impact ionization and knocking out electrons from the cathode by positive ions.
This discharge is used mainly for lighting. Used in fluorescent lamps.

The word “plasma” (from the Greek “plasma” - “formed”) in mid-19th V. began to be called the colorless part of the blood (without red and white cells) and the liquid that fills living cells. In 1929, American physicists Irving Langmuir (1881-1957) and Levi Tonko (1897-1971) called ionized gas in a gas discharge tube plasma. The English physicist William Crookes (1832-1919), who studied electric discharge in tubes with rarefied air, wrote: “Phenomena in evacuated tubes open up a new world for physical science, in which matter can exist in a fourth state.” Depending on the temperature, any substance changes its state. Thus, water at negative (Celsius) temperatures is in a solid state, in the range from 0 to 100 ° C - in a liquid state, above 100 ° S-in gaseous. If the temperature continues to rise, atoms and molecules begin to lose their electrons - they become ionized and the gas turns into plasma. At temperatures above 1,000,000 °C, plasma is completely ionized - it consists only of electrons and positive ions. Plasma is the most common state of matter in nature, accounting for about 99% of the mass of the Universe. The Sun, most stars, nebulae are completely ionized plasma. External part earth's atmosphere(ionosphere) is also plasma. Even higher are the radiation belts containing plasma. Auroras, lightning, including ball lightning, are all different types of plasma that can be observed under natural conditions on Earth. And only an insignificant part of the Universe is made up of solid matter - planets, asteroids and dust nebulae. In physics, plasma is understood as a gas consisting of electrically charged and neutral particles, in which the total electric charge equal to zero, t.s. the condition of quasineutrality is satisfied (therefore, for example, a beam of electrons flying in a vacuum is not plasma: it carries a negative charge). PLASMA - a partially or fully ionized gas in which the densities are positive and negative charges almost identical. IN laboratory conditions plasma is formed in an electrical discharge in a gas, in the processes of combustion and explosion. When the laser beam was focused by a lens, a spark flashed in the air in the focal area, and plasma was formed there. This aroused great interest among physicists. The first seed electrons appear as a result of their ejection from the atoms of the medium after the simultaneous absorption of several photons of a light wave. The energy of each ruby ​​laser photon is 1.78 eV. Next, the free electron, absorbing photons, reaches an energy of 10 eV, sufficient for ionization and the birth of a new electron in the process of collision with atoms of the medium. The discharge can burn for a long time and glows with a blinding white light, it is impossible to look at it without dark glasses. An unusually high temperature - a unique property of an optical charge - represents great opportunities to use it as a light source. The ability to create a plasma filament using laser light opens up the possibility of transmitting energy over a distance. Charge carriers in plasma are electrons and ions formed as a result of gas ionization. The ratio of the number of ionized atoms to their total number per unit volume of plasma is called the degree of plasma ionization (a). Depending on the value of a, one speaks of weakly ionized (a - fractions of a percent), partially ionized (a - several percent) to completely ionized (a is close to 100%) plasma. Average kinetic energies various types The particles that make up the plasma can be different. Therefore in general case plasma is characterized not by one temperature value, but by several - a distinction is made between the electronic temperature Te, the ion temperature Ti and the temperature of neutral atoms Ta. Plasma with ion temperature Ti< 105 К называют низкотемпературной, а с Тi >106 K - high temperature. High-temperature plasma is the main object of research in controlled thermonuclear fusion (CTF). Low temperature plasma is used in gas discharge sources light, gas lasers, MHD generators, etc. Plasma is most widely used in lighting technology - in gas-discharge lamps that illuminate streets and fluorescent lamps used indoors. And in addition, in a wide variety of gas-discharge devices: electric current rectifiers, voltage stabilizers, plasma amplifiers and microwave generators, meters cosmic particles. All so-called gas lasers (helium-neon, krypton, carbon dioxide, etc.) are actually plasma: gas mixtures they are ionized by an electric discharge. Conduction electrons in the metal have properties characteristic of plasma (ions, rigidly fixed in the crystal lattice, neutralize their charges), a combination free electrons and mobile “holes” (vacancies) in semiconductors. Therefore, such systems are called plasma solids Gas plasma is usually divided into low temperature - up to 100 thousand degrees and high temperature - up to 100 million degrees. There are generators of low-temperature plasma - plasmatrons, which use an electric arc. Using a plasma torch, you can heat almost any gas to 7000-10000 degrees in hundredths and thousandths of a second. With the creation of the plasma torch, arose new area science - plasma chemistry: many chemical reactions are accelerated or occur only in a plasma jet. Plasmatrons are used in the mining industry and for cutting metals. Plasma engines and magnetohydrodynamic power plants have also been created. Under development various schemes plasma acceleration of charged particles. The central problem of plasma physics is the problem of controlled thermonuclear fusion. Thermonuclear reactions are reactions of the synthesis of heavier nuclei from the nuclei of light elements (primarily isotopes of hydrogen - deuterium D and tritium T), occurring at very high temperatures (» 108 K and above). Under natural conditions, thermonuclear reactions occur in the Sun: hydrogen nuclei combine with each other with each other, forming helium nuclei, while releasing significant amount energy. An artificial thermonuclear fusion reaction was carried out in a hydrogen bomb.

An arc discharge (hereinafter referred to as DR) can be implemented either independently or non-independently. Independent d.b. can be obtained from a glow discharge by increasing the current density (1÷100 A/cm 2) An arc discharge differs from a glow discharge in the processes of electron emission from the cathode. The main types of emissions are thermal and auto-electronic emissions. In dr. the near-cathode potential drop is several tens of volts and is close to the ionization potential of gas atoms. All dr. classified according to 2 criteria:

1) According to the predominant type of emission - the main type of emission is thermionic. "arc with a hot cathode", and with field electronic - "arc with a cold cathode."

2) By the type of environment in which the arc discharge burns: a) an arc in an atmosphere of gas or a mixture of gases - b) an arc in vapors of the cathode or anode material -

The main element of the arc is the cathode spot, which provides intense emission, has a high brightness of glow, the sharp boundary of the cathode spot is determined by the dependence of the glow intensity on temperature. All arc discharges have a positive column connected to the cathode spot called the arc brush.

To stabilize the position of a positive column in space, 3 main methods are used:

1) stabilization by walls; used in arc fluorescent lamps (DRL, DN)

2) stabilization of the column by gas or liquid flows

3) stabilization with electrodes. A short arc is realized with high strength current with temp. plasma in the positive column is about 10 4 K. Such arcs are used in DRSh, DKSSh, DKSL lamps.

Parameters d.r. is largely determined by the gas pressure in the positive column - low pressure arc - medium pressure arc - high pressure arc

Low pressure arcs: pressure range from 1 to 10 mm. rt. Art. , the current density at the cathode can reach 10 8 A/cm 2 , the mechanisms of electron emission have not yet had a similar description. Characteristic feature is that when the pressure increases above 10 mm. rt. Art. leads to a sharp decrease in the cross-sectional area of ​​the column. This effect is called contraction. The “+” plasma of the low-pressure arc column is a non-isothermal plasma, in which the electron temperature is 1-2 orders of magnitude higher than the temperature of atoms and ions. When a “+” column is formed, the loss of charged particles due to bipolar diffusion onto the walls decreases, resulting in a decrease in the proportion of discharge energy spent on the walls. As the pressure increases, the low-pressure arc transforms into a high-pressure arc, in which the main processes in the “+” column change. In the low-pressure region, the elementary processes of the “+” column are qualitatively similar to the processes of a glow discharge.

There are no step processes in the low pressure region. As pressure increases, the efficiency of step processes increases and the frequency of collisions increases. During its lifetime, the atom experiences additional collisions => the intensity of the lines corresponding to transitions between m/y excited states increases. The fraction of radiation will increase in the long-wave region because the lifetime is large, the efficiency of inelastic impacts of the 2nd kind increases => the electron temperature begins to approach the temperature of heavy particles with an average increase.

Depending on the gas pressure, electrode configuration and external circuit parameters, there are four types of independent discharges:

• glow discharge;
• spark discharge;
• arc discharge;
• corona discharge.

1. Glow discharge occurs at low pressures. It can be observed in a glass tube with flat metal electrodes soldered at the ends (Fig. 8.5). Near the cathode there is a thin luminous layer called cathode luminous film 2.

Between the cathode and the film there is Aston's dark space 1. To the right of the luminous film is placed a weakly luminous layer called cathode dark space 3. This layer goes into a luminous area, which is called smoldering glow 4, the smoldering space is bordered by a dark gap - Faraday dark space 5. All of the above layers form cathode part glow discharge. The rest of the tube is filled with glowing gas. This part is called positive column 6.

As the pressure decreases, the cathode part of the discharge and the Faraday dark space increase, and the positive column shortens.

Measurements showed that almost all potential drops occur in the first three sections of the discharge (Aston's dark space, cathode luminous film and cathode dark spot). This portion of the voltage applied to the tube is called cathode potential drop.

In the region of the smoldering glow, the potential does not change - here the field strength is zero. Finally, in the Faraday dark space and the positive column, the potential slowly increases.

This potential distribution is caused by the formation of a positive space charge in the cathode dark space due to increased concentration positive ions.

Positive ions, accelerated by the cathode potential drop, bombard the cathode and knock electrons out of it. In the Aston dark space, these electrons, flying without collisions into the region of the cathode dark space, have high energy, as a result of which they more often ionize molecules than excite them. Those. The intensity of the gas glow decreases, but many electrons and positive ions are formed. The resulting ions initially have a very low speed and therefore a positive space charge is created in the cathode dark space, which leads to a redistribution of potential along the tube and the occurrence of a cathode potential drop.

Electrons generated in the cathode dark space penetrate into the region of smoldering glow, which is characterized by a high concentration of electrons and positive ions and a polar space charge close to zero (plasma). Therefore, the field strength here is very low. In the region of the smoldering glow, an intense recombination process takes place, accompanied by the emission of energy released during this process. Thus, the smoldering glow is mainly a recombination glow.

From the region of smoldering glow into Faraday dark space, electrons and ions penetrate due to diffusion. The probability of recombination here drops greatly, because the concentration of charged particles is low. Therefore, there is a field in Faraday dark space. The electrons entrained by this field accumulate energy and often eventually create the conditions necessary for the existence of a plasma. The positive column represents gas-discharge plasma. It acts as a conductor connecting the anode to the cathode parts of the discharge. The glow of the positive column is caused mainly by transitions of excited molecules to the ground state.

2. Spark discharge occurs in gas usually at pressures on the order of atmospheric pressure. It is characterized by an intermittent form. In appearance, a spark discharge is a bunch of bright zigzag branching thin stripes that instantly penetrate the discharge gap, quickly extinguish and constantly replace each other (Fig. 8.6). These strips are called spark channels.

T gas = 10,000 K ~ 40 cm I= 100 kA t= 10 –4 s l~ 10 km

After the discharge gap is “pierced” by the spark channel, its resistance becomes small, a short-term pulse of high current current passes through the channel, during which only a small voltage falls on the discharge gap. If the source power is not very high, then after this current pulse the discharge stops. The voltage between the electrodes begins to increase to its previous value, and the gas breakdown is repeated with the formation of a new spark channel.

In natural natural conditions the spark discharge is observed in the form of lightning. Figure 8.7 shows an example of a spark discharge - lightning, duration 0.2 ÷ 0.3 with a current strength of 10 4 - 10 5 A, length 20 km (Fig. 8.7).



3. Arc discharge . If, after receiving a spark discharge from a powerful source, the distance between the electrodes is gradually reduced, then the discharge from intermittent becomes continuous, and a new form gas discharge, called arc discharge(Fig. 8.8).

~ 10 3 A
Rice. 8.8

In this case, the current increases sharply, reaching tens and hundreds of amperes, and the voltage across the discharge gap drops to several tens of volts. According to V.F. Litkevich (1872 - 1951), the arc discharge is maintained mainly due to thermionic emission from the cathode surface. In practice, this means welding, powerful arc furnaces.

4. Corona discharge (Fig. 8.9).occurs in a strong non-uniform electric field at relatively high gas pressures (on the order of atmospheric). Such a field can be obtained between two electrodes, the surface of one of which has a large curvature (thin wire, tip).

The presence of a second electrode is not necessary, but its role can be played by nearby, surrounding grounded metal objects. When the electric field near an electrode with a large curvature reaches approximately 3∙10 6 V/m, a glow appears around it, looking like a shell or crown, which is where the name of the charge comes from.

1. Arc formation.

arc discharge .

.

4. Temperature and radiation of individual parts of the arc discharge.

tric arc.

and ultra-high pressure.

III. Application of arc discharge.

1. Modern methods of electrical processing.

2. Electric arc welding.

3.Plasma technology.

4.Plasma welding.
IV. Conclusion.

An arc discharge in the form of a so-called electric (or voltaic) arc was first discovered in 1802 by the Russian scientist, professor of physics at the Military Medical-Surgical Academy in St. Petersburg, and later academician of the St. Petersburg Academy of Sciences Vasily Vladimirovich Petrov. In one of the books he published, Petrov describes his first observations of the electric arc in the following words:

“If two or three charcoals are placed on a glass tile or on a bench with glass legs... and if metal insulated guides... communicated with both poles of a huge battery are brought closer to each other at a distance of one to three lines, then between them appears a very bright white light or flame, from which these coals ignite faster or more slowly and from which the dark peace can be quite clearly illuminated...”

The path to the electric arc began in ancient times. Even the Greek Thales of Miletus, who lived in the sixth century BC, knew the property of amber to attract light objects such as feathers, straw, hair when rubbed, and even create sparkles. Until the seventeenth century, this was the only way to electrify bodies, which had no practical application. Scientists were looking for an explanation for this phenomenon.

The English physicist William Gilbert (1544-1603) found that other bodies (for example, rock crystal, glass), like amber, have the property of attracting light objects after rubbing. He called these properties electrical, introducing this term into use for the first time (in Greek, amber is electron).

The burgomaster of Magdeburg, Otto von Guericke (1602-1686), designed one of the first electric machines. It was an electrostatic machine, which was a sulfur ball mounted on an axis. One of the poles was... the inventor himself. When the handle was rotated, bluish sparks flew out from the palms of the satisfied burgomaster with a slight crackling sound. Later, Guericke's machine was improved by other inventors. The sulfur ball was replaced by a glass one, and instead of the researcher’s palms, leather pads were used as one of the poles.

Of great importance was the invention in the eighteenth century of the Leyden jar-capacitor, which made it possible to store electricity. It was a glass vessel filled with water, wrapped in foil. A metal rod passed through a stopper was immersed in water.

The American scientist Benjamin Franklin (1706-1790) proved that water does not play any role in the collection of electrical charges; dielectric glass has this property.

Electrostatic machines have become quite widespread, but only as fun gizmos. There were, however, attempts to treat patients with electricity, but it is difficult to say what the physiotherapeutic effect of such treatment was.

The French physicist Charles Coulomb (1736-1806), the founder of electrostatics, established in 1785 that the force of interaction between electric charges is proportional to their magnitudes and inversely proportional to the square of the distance between them.

In the forties of the eighteenth century, Benjamin Franklin put forward the theory that there is only one kind of electricity - a special electrical matter consisting of tiny particles capable of penetrating into matter. If a body has an excess of electrical matter, it is charged positively; if there is a deficiency, the body is negatively charged. Franklin introduced the plus and minus signs into practice, as well as the terms: capacitor, conductor, charge.

Original theories about the nature of electricity were made by M. V. Lomonosov (1711-1765), Leonhard Euler (1707-1783), Franz Apinus (1724-1802) and other scientists. By the end of the eighteenth century, the properties and behavior of stationary charges had been sufficiently studied and, to some extent, explained. However, nothing was known about electric current-moving charges, since there was no device that could make a large number of charges move. The currents received from the electrostatic machine were too small to be measured.

1 . If you increase the current in a glow discharge, reducing the external resistance, then at a high current, the voltage at the tube terminals begins to fall, the discharge quickly develops and turns into an arc. In most cases, the transition occurs abruptly and almost often leads to a short circuit. By selecting the resistance of the external circuit, it is possible to stabilize the transition form of the discharge and observe, at certain pressures, the continuous transition of the glow discharge into an arc. In parallel with the voltage drop between the electrodes of the tube, there is an increase in the cathode temperature and a gradual decrease in the cathode drop.

The use of the usual method of igniting an arc by moving the electrodes apart is due to the fact that the arc burns at relatively low voltages of tens of volts, while to ignite a glow discharge a voltage of the order of tens of kilovolts is needed at atmospheric pressure. The ignition process when moving the electrodes apart is explained by local heating of the electrodes due to the formation of poor contact between them at the moment the circuit breaks.

The question of the development of an arc when a circuit breaks is technically important not only from the point of view of obtaining “useful” arcs, but also from the point of view of combating “harmful” arcs, for example, with the formation of an arc when a switch is opened. Let L be the self-inductance of the circuit, W be its resistance, ع be the e.m.f. current source, U(I) is a function of the current-voltage characteristic of the arc. Then we must have: ع= L dI/dt+WI+U(I) (1) or

LdI/dt=(ع-WI)-U(I)=∆ (2).

The difference (ع - WI) is nothing more than the ordinate of the direct resistance AB (Fig. 1), and U(I) is the ordinate of the arc characteristic for a given I. So that dI/dt is negative, i.e. So that the current I certainly decreased over time and no stable arc formed between the electrodes of the switch, it is necessary that

Fig.1. The relative position of the resistance line and the current-voltage characteristic curve of a steady arc for the cases: a) when the arc cannot occur when the circuit breaks; b) when an arc occurs during a break in the current range corresponding to points P and Q.

∆ ع-WI took place.

To do this, the characteristic with all its points must lie above the resistance line (Fig. 1, a). This simple conclusion does not take into account the capacitances in the circuit and applies only to direct current.

The point of intersection of the resistance line with the current-voltage characteristic curve of a steady arc corresponds to the lowest limit of direct current strength at which an arc can occur when the circuit breaks (Fig. 1, b). In the case of a switch opening an alternating current arc that goes out with each voltage transition through zero, it is essential that the conditions present in the discharge gap during opening do not allow the arc to re-ignite with a subsequent increase in the voltage of the current source. This requires that as the voltage increases, the discharge gap is sufficiently deionized. In switches of strong alternating currents, enhanced deionization is artificially achieved by introducing special electrodes that suck out charged gas particles due to bipolar diffusion, as well as by using mechanical blowing or by exposing the discharge to a magnetic field. At high voltages, oil switches are used.

2 . The cathode spot, stationary on the carbon cathode, on the surface of liquid mercury is in continuous rapid movement. The position of the cathode spot on the surface of liquid mercury can be fixed using a metal pin immersed in the mercury and protruding slightly from it.

In the case of a small distance between the anode and the cathode, the thermal radiation of the anode greatly affects the properties of the cathode spot. At a sufficiently large distance of the anode from the carbon cathode, the dimensions of the cathode spot tend to some constant limiting value, and the area occupied by the cathode spot on the carbon electrode in air is proportional to the current strength and corresponds to an atmospheric pressure of 470 A/cm². For a mercury arc 4000 a/cm² was found in vacuum.

As the pressure decreases, the area occupied by the cathode spot on the carbon cathode at a constant current increases.

The sharpness of the visible boundary of the cathode spot is explained by the fact that a relatively slow decrease in temperature with distance from the center of the spot corresponds to a rapid drop in both light radiation and thermionic emission, and this is equivalent to sharp “optical” and “electrical” boundaries of the spot.

When an arc burns in air, the carbon cathode becomes sharp, while on the carbon anode, if the discharge does not cover the entire front area of ​​the anode, a round depression is formed - positive arc crater.

The formation of a cathode spot is explained as follows. The distribution of space charges in a thin layer near the cathode is such that the discharge requires the smaller the cross-section of the discharge channel to maintain it, the smaller the potential difference. Therefore, the discharge at the cathode must contract.

Directly adjacent to the cathode spot is a part of the discharge called the negative cathode brush or negative flame. The length of the cathode brush in the arc at low pressure is determined by the distance over which the fast primary electrons fly, having received their velocities in the region of the cathode potential drop.

Between the negative brush and the positive column there is an area similar to the Faraday dark space of a glow discharge. In Petrov's arc in the air, in addition to the negative brush, there is a positive flame and a number of halos. Spectral analysis indicates the presence of a number of chemical compounds (cyanine and nitrogen oxides) in these flames and halos.

With a horizontal arrangement of the electrodes and high gas pressure, the positive column of the arc discharge bends upward under the influence of convection currents of the gas heated by the discharge. This is where the name arc discharge comes from.

3 . In the Petrov arc, high temperature and high pressure do not make it possible to use the probe method to measure the potential distribution.

The potential drop between the arc electrodes consists of the cathode drop and Uk, the anodic drop Ua and the drop in the positive column. The sum of the cathode and anode potential drops can be determined by bringing the anode and cathode closer together until the positive column disappears and measuring the voltage between the electrodes. In the case of an arc at low pressure, it is possible to determine the potential values ​​​​at two points of the arc column using the method of probe characteristics, calculate the longitudinal potential gradient from here and then calculate both the anodic and cathodic potential drop.

It has been established that in an arc discharge at atmospheric pressure the sum of the cathode and anode drops is approximately the same value as the ionization potential of the gas or vapor in which the discharge occurs.

In the technique of using Petrov's arc with carbon electrodes, the empirical Ayrton formula is usually used:

U=a+bl+(c+dl)/I (3)

Here U is the voltage between the electrodes, I is the current strength in the arc, l is the length of the arc, a, b, c and d are four constants. The characteristic formula (3) is established for an arc between carbon electrodes in air. By l we mean the distance between the cathode and the plane drawn through the edges of the positive crater.

Let us rewrite formula (4) in the form

U=a+c/I+l(b+d/I). (4)

In (4), terms containing the factor l correspond to the potential drop in the positive column; the first two terms represent the sum of the cathode and anode drop Uк+Uа. The constants in (3) depend on the air pressure and the cooling conditions of the electrodes, and therefore on the size and shape of the coals.

In the case of an arc discharge in an evacuated vessel filled with metal vapor (for example, mercury), the vapor pressure depends on the temperature of the coldest parts of the vessel and therefore the course of the characteristic strongly depends on the cooling conditions of the entire tube.

The dynamic characteristics of an arc discharge are very different from the static ones. The type of dynamic characteristic depends on the speed of change of the arc mode. In practice, the most interesting characteristic of the arc is when powered by alternating current. Simultaneous oscillography of current and voltage gives the picture shown in Fig. 2. The characteristic of the arc drawn from these curves for the entire period has

view shown in Fig. 3. The dotted line shows the voltage progression in the absence of a discharge.

Fig.4. Dynamic characteristics

arc discharge tick on

low frequency alternating current.

Is. 3. Oscillogram of current and voltage of arc discharge on alternating current

low frequency. Points A, B, C, etc.

correspond to the points indicated by those

the same letters in Fig. 4.

The cathode, which has not yet had time to cool after the discharge that took place in the previous half-cycle of the current, from the very beginning of the half-cycle, when the external emf. passes through zero and emits electrons. From point O to point A, the characteristic corresponds to a non-self-sustaining discharge, the source of which is the electrons emitted by the cathode. At point A the arc is ignited. After point A, the discharge current increases rapidly. If there is resistance in the external circuit, the voltage between the arc electrodes drops, although the emf. current source (dotted line in Fig. 3), running through a sinusoid, increases even more. As the voltage and current supplied by the external source decrease, the discharge current begins to decrease.

With a decrease in the current in the arc, the voltage between its electrodes may increase again depending on the external resistance, but part of the BC characteristic in Fig. 4 may be horizontal or have the opposite slope. At point C the arc goes out.

After point C, the non-self-sustaining discharge current decreases to zero along with a decrease in the voltage between the electrodes.

P
after the voltage passes through

zero, the role of the cathode begins to be played by the previous anode and the picture is repeated with opposite signs of current and voltage.

Fig.5. Change in dynamic characteristics at increased frequency of alternating current superimposed on direct current.

If an alternating voltage of an amplitude less than the voltage of the direct current feeding the arc is applied to the electrodes of an arc fed by direct current, then the characteristic takes the form of a closed loop covering the static characteristic Sun on both sides. As the frequency of alternating current increases, the axis of this loop rotates, the loop itself is flattened and, finally, tends to take the form of a straight line segment OA, passing through the origin of coordinates (Fig. 5). At a very low frequency, the loop of the dynamic characteristic turns into a segment of the static characteristic of the VS, since all internal parameters of the discharge, in particular the concentration of ions and electrons, manage to take on values ​​at each point of the characteristic that correspond to a stationary discharge for given U and I. Vice versa , with a very rapid change, the discharge parameters do not have time to change at all, therefore I turns out to be proportional and, which corresponds to the straight line OA passing through the origin of coordinates. Thus, with an increase in the frequency of the alternating current, the characteristic loop (Fig. 5) becomes in all its increasing points.

Due to the possibility of complete ionization of gas in an arc

discharge there is a question of arc breakage at low gas pressure

and very strong currents. A significant decrease in gas density due to electrophoresis and suction of ions to the walls plays a significant role in the phenomenon of arc breakage, especially in places where the discharge gap is greatly narrowed. In practice, this leads to the need to avoid excessive contractions when constructing mercury rectifiers for very high currents.

Electricians who dealt with electric arcs for the first time

tried to apply Ohm's law in this case as well. To obtain calculation results according to Ohm's law that agree with reality, they had to introduce the concept of the inverse electromotive force of the arc. By analogy with phenomena in galvanic cells, the expected appearance of this emf. called arc polarization. The question of reverse emf. The arcs are devoted to the works of Russian scientists D. A. Lachinov and V. F. Mitkevich. Further development of ideas about electrical discharges in gases showed that such a formulation of the question is purely formal and can be successfully replaced by the idea of ​​​​the falling characteristic of the arc. The validity of this point of view is confirmed by the failure of all attempts to directly detect experimentally the reverse emf. electric arc.

4 . In the case of an arc in air between carbon electrodes

The radiation from hot electrodes, mainly from the positive crater, predominates.

The radiation of the anode, like the radiation of a solid body, has

continuous spectrum. Its intensity is determined by the temperature of the anode. The latter is a characteristic value for an arc in atmospheric air with an anode made of any given material, since the temperature of the anode does not depend on the current strength and is determined solely by the melting or distillation temperature of the anode material. The melting or sublimation temperature depends on the pressure under which the melting or sublimating body is located. Therefore, the anode temperature, and therefore the intensity of the positive crater radiation, depends on the pressure at which the arc burns. In this regard, classical experiments with a carbon arc under pressure are known, which led to very high temperatures.

On the change in the temperature of a positive crater with pressure

This drawing contains points for pressures from 1 atm

and above, serves as confirmation of the assumption that the temperature of the positive crater is determined by the temperature of melting or sublimation of the anode substance, since in this case there should be a linear relationship between ln r and 1/T. The deviation from the linear dependence at lower pressures is explained by the fact that at pressures below 1 atm, the amount of heat released at the anode is insufficient for

Rice. 6. Change in temperature of the carbon anode of an electric dkg in air with a change in pressure. The scale along the ordinate axis is logarithmic.

The temperature of the cathode spot of the Petrov arc is always several

hundreds of degrees below the temperature of the positive crater.

High arc cord temperatures cannot be detected

using a thermocouple or bolometer. Currently

to determine the temperature in the arc, spectral

At high current strengths, the gas temperature in Petrov's arc

may be higher than the anode temperature and reaches 6000° K. Such high gas temperatures are characteristic of all cases of arc discharge at atmospheric pressure. In the case of very high pressures (tens and hundreds of atmospheres), the temperature in the central parts of the detached positive arc column reaches 10,000° K. In an arc discharge at low pressures, the gas temperature in the positive column is of the same order as in the positive column of a glow discharge.

The temperature of the positive arc crater is higher than the temperature of the cathode, because at the anode all the current is carried by electrons bombarding and heating the anode. Electrons

donate to the anode not only everything purchased in the anode area

drop in kinetic energy, but also the work function (“hidden-

heat of evaporation" of electrons). On the contrary, to the cathode

falls and is bombarded and heated by a small number of positive ions compared to the number of electrons hitting the anode at the same current strength. The rest of the current on the cathode is carried out by electrons, upon the exit of which in the case

thermionic arc, heat is expended on the work function

vaya energy of the cathode.

5 . Due to the fact that the arc has a falling characteristic, it can be used as a generator of continuous oscillations. The diagram of such an arc generator is shown in Fig. 7. Conditions for generating oscillations in this

With
heme can be deduced from consideration

friction conditions of stability of the

national rank for given

parameters of the external circuit.

Let the electromotive force

DC source, pi-

Rice. 7. Schematic diagram of an arc generator.

voltage between electrodes

tubes U, stationary power

flow through the discharge tube in this mode is equal to I, the cathode-anode capacitance of the tube plus the capacitance of all supply wires C, self-inductance in the circuit L, the resistance through which current is supplied from the source, R. Under steady-state DC mode, we will have:

ع= UO+IR(5)

Let us assume that this stationary regime is violated. Bit

the current at any given time is equal to I+i, Where i-small value, and the potential difference between the electrodes is equal to U.

Let us introduce the notation

(dU/d i)i=0 is equal to the tangent of the tangent to the current-voltage characteristic at the operating point corresponding to the mode we initially selected (current I). Let's see how it will change further i. If i will increase, then this discharge mode is unstable; if, on the contrary, i decreases indefinitely, then the discharge mode is stable.

Let us turn to the current-voltage characteristic of the considered

discharge gap U= f(I+i) - Current flows through the tube

I+i and capacity WITH is charging (or discharging). Difference

potentials on the capacitance WITH is balanced in this case

not only by the voltage across the discharge gap, but also by the emf.

self-inductance of the circuit. Let I+i2 -total current through the resistance-

tion R. Let us denote the current charging the capacitance C by i1 ; instantly

the real value of the potential difference across the capacitance C- through U1. The potential difference between the arc electrodes will be U0 +iU’.

ع =U1 +(i+I2 )R, (6)

U1 -U0 =U'i+Ldi/dt, (7)

i2 =i1 +i. (8)

Additional charge Q on capacity C compared to stationary mode:

Q=∫i 1 dt=(U 1 -U 0)C. (9)

Subtracting (5) from (6), we find:

U 1 -U 0 =-i 2 R (10)

Expressions (7), (8) and (10) give:

U"i+Ldi/dt=-R(i+i 1 ) . (11)

Expressions (7) and (9) give:

1/C∫ i 1 dt=U'i+Ldi/dt. (12)

Differentiating (12) with respect to t and inserting the result into (11), we find:

U’i+Ldi/dt=-iR-RCU’di/dt-RLCdІ i/dtІ . (13)

dІ i/dtІ +(1/CR+U’/L)di/dt + 1/LC(U’/R+1)i=0 (14)

Formula (14) is a differential equation,

to which the additional current is subject i.

As is known, the complete integral of equation (14) has the form:

i=A1e^r1t+A2e^r2t, (15)

where r1 and r2 are the roots of the characteristic equation, determined by the formula

r=-1/2(1/CR+U’/L)+ √1/4(1/CR+U’/L)І-1/LC(U’/R+1). (16)

If the radical value in (16) is greater than zero, then r1 and r2

both are real, i changes aperiodically according to an exponential law, and solution (15) corresponds to an aperiodic change in current. In order for current oscillations to occur in the circuit we are considering, it is necessary that r 1 and r 2 be complex quantities, i.e.

1/LC(U’/R+1)>1/4(1/CR+U’/L)І(17)

In this case, (15) can be represented as

i=A 1 e -δt+jωt +A 2 e -δt-jωt , (18)

δ=1/2(1/CR+U’/L); i=√-1.

At δ δ > 0 they quickly decay, and the discharge at a constant current will be stable.

Thus, in order for undamped oscillations to eventually be established in the circuit under consideration, it is necessary that

(1/CR+U’/L) (19)

Since P, L and C are essentially positive quantities, then

inequality (19) can be satisfied only under the condition:

From here we conclude that oscillations in the circuit under consideration

can arise only with a falling current-voltage characteristic

risk of discharge.

Investigation of the conditions under which r1 and r2 are valid

and both are less than zero, leading to discharge stability conditions

DC:

(1/CR+U’/L)>0And (21)

U'/R+1>0 . (22)

Conditions (21) and (22) are general conditions

Stability of discharge powered by constant voltage. From

(21) it follows that with increasing current-voltage characteristics

In reality, the discharge is always stable.

Combining this requirement with condition (22), we find that

with a falling characteristic, the discharge can be stable

only when

When directly applying the formulas of this paragraph

to the question of generating oscillations using an arc

take U" from the “average characteristic”, built on the basis of the ascending and descending branches of the dynamic characteristic.

With a periodic change in the current strength in the Petrov arc due to

the temperature and density of the gas and the speed of aerodynamic flows change. When selecting the appropriate mode, these

changes lead to acoustic vibrations

in the surrounding air. The result is a so-called singing arc, reproducing pure musical tones.

6 . With increasing gas pressure and increasing current density, the temperature along the axis of the positive column, detached from the walls of the discharge tube, rises more and more. Ionization processes begin to take on a character more and more consistent with purely thermal ionization. The average kinetic energy of plasma electrons approaches the average kinetic energy of neutral gas particles. The plasma becomes close in its properties to isothermal

chesky plasma. All this allows us to solve the problem of finding

various discharge parameters, including the number of longitudinal field gradient depending on the discharge current density, based on thermodynamic relationships.

The starting points of the theory of the positive arc column

The second discharge at high and ultra-high pressure is the Sag equation for thermal ionization in the form

αІp=AT 5/2 e -eUi/kT (24)

and Boltzmann's theorem in the form of the relation

n a =nge (-eU a /kT) (25)

Here α is the degree of ionization, p is the gas pressure, A is the constant,

T-gas temperature, U i -ionization potential, k-constant

Boltzmann, “n a is the concentration of excited atoms, n-concentration

tration of normal atoms, U a -excitation potential, g-relative

determination of the statistical weights g a /g n of the excited and normal states of the atom. The temperature of the electron gas is assumed to be equal to the temperature of the neutral gas. To simplify the problem, only one “average” level of excitation is taken into account. The discharge tube is assumed to be located vertically. In any other position, convection gas flows distort the axial symmetry of the gas regime.

Let us denote the inner radius of the discharge tube by R1, and the distance of any point from the axis of the tube by r. Let's carry out

at a distance of one centimeter from one another there are two sections perpendicular to the axis of the tube, and we select an elementary volume between them using two concentric cylinders with radii r and r+dr (Fig. 8). Let us denote the amount of energy released by the discharge per unit time per unit tube length by N1, and the amount of energy per unit volume under consideration by dN1. Amount of energy emitted per unit
time is a gas enclosed

per unit length of the entire tube and

in the elementary

volume, denoted by S1 and dS1.

Inside the tube there is

Rice. 8. Volume element in an axially symmetric discharge.

heat through the gas in the direction

from the axis to the wall. Let us denote by dL1 the excess of the amount of heat leaving the volume element under consideration through its outer boundary per unit of time over the amount of heat penetrating into the same volume per unit of time through its inner boundary from the side of the tube axis. Let us assume that the convection flows of gas are strictly vertical and do not violate the thermal regime of the gas.

The condition for the thermal balance of the elemental element under consideration

volume will be written in general form like this:

dN1 =dL1 +dS1 . (26)

Due to the presence of axial symmetry, all quantities characterized by

representing the state of the gas and the discharge mode are the same for

points located at the same distance r from the axis.

Since the area of ​​the base of the elementary element under consideration

volume is equal to 2пrdr, then for the power released in this

volume, we can write:

dN 1 =2 nri r E z dr, (27)

where i r is the current density at a distance r from the axis, and E z is the longitudinal field gradient, the same over the entire cross section of the tube. Denoting the coefficient of thermal conductivity of a gas at temperature T by λ t, we write for dL 1, neglecting terms of higher order of smallness:

dL 1 =2п(r+dr)(λ t dT/dr) r+dr -2пr(λ t dT/dr) r =2пd(rλ t dT/dr)/dr (28)

Let us assume that the energy emitted by the gas leaves entirely

discharge gap without noticeable reabsorption in the gas. This

The assumption can be made because the resonant radiation absorbed by the gas at high pressure constitutes only a small fraction of the total radiation of the gas. Since the energy emitted per unit time is proportional to the concentration of excited atoms na, then for dS 1 we can write:

dS 1 =2пrCn a dr, (29)

where C is a constant factor independent of T. Substitution

values ​​(29) and (28) in (26) gives:

2 nri r E z dr=2nd(rλ T dT/dr)dr/dr + 2nrCn a dr (30)

Neglecting the small fraction of current attributable to the polar

resident ions, and denoting the mobility of electrons through K e, we can write:

i=n e eK e E z . (31)

If we denote the right side of the Saga equation (24) by f 1 (T), and replace p on the left side with nkT, where n is the concentration of neutral gas particles, then we find:

α 2 = f 1 (T)/ nkT. (32)

n is proportional to the mass of gas contained in a unit length

tube, g 1 and inversely proportional to the square of the radius of the tube R1 and the gas temperature at a given point:

n=C 1 g 1 /TR 1 2 (33)

Therefore, instead of (32) we can write:

α= R 1 √f1(T)/C1k/ √g 1 =R 1 f 2 (T)/√g 1 (34)

According to Langevin's equation, the speed of electron movement

in a gas in a field of intensity E z is equal to:

u=K e E z =aeλ e E z /mv (35)

where v is the arithmetic mean speed of thermal movement

electrons, is directly proportional to the square root of the temperature of the electron gas, while λ e is inversely proportional to n. Hence,

K e =C 2 /nT 1/2 (36)

According to the definition of α:

From (31), (34), (37) and (36) it follows:

i r =E z R i C 2 f 2 (T)/g 1 1/2 T 1/2 (38)

where T is the gas temperature at a distance r from the axis. From (38)

and (27) follows:

dN 1 =2пrE r 2 R 1 C 2 f 2 (T)dr/g 1 1/2 T 1/2 =2пrE z 2 R 1 f 3 (T)dr/g 1 1/2 ,(39)

According to the Boltzmann equation (25):

n a =nge (-eU a /kT) =C 1 gg 1 e (-eU a /kT) /TR 1 2 =g 1 f 4 (T)/ R 1 2, (40)

where f 4 (T)= C 1 ge (-eU a /kT) /T.

Inserting this value of n a into (29) and replacing Cf 4 (T) through f 5 (T), we find:

dS 1 =g 1 2пrf 5 (T)dr/R 1 2 . (41)

Substituting (39), (28) and (41) into (26) gives

E r 2 R 1 f 3 (T)/g 1 1/2 =d(rλ t dT/dr)/rdr+g 1 f 5 (T)dr/R 1 2 (42)

In equation (42), f 3 (T) and f 5 (T), as well as λ t, are functions of the variable T alone. Therefore, (42) is

differential equation connecting the variables T and r.

Boundary conditions that the solution must satisfy

of this equation are: a) at r=R the condition T=T st, where T st is the temperature of the discharge tube wall; b) at r=0, the condition dT/dr = 0, since on the axis of the tube the gas temperature has a maximum value.

All quantities characterizing the discharge are functions

from just one T. Therefore, the solution to equation (42) could

would provide a complete solution to all quantitative issues associated with this type of discharge. However, the significance of equation (42) lies mainly in the fact that by moving to dimensionless quantities it leads to similarity laws characteristic of a given type of discharge, which make it possible to transfer quantitative results established experimentally for the same values ​​of N 1, R 1 and g 1 for the discharge mode at other values ​​of these quantities. This technique is similar to that used to solve some problems of hydrodynamics, also only on the basis of the analysis of the differential equation and experimental measurements on models constructed in accordance with the similarity laws of hydrodynamics. In this case, two discharges are similar, in which at the corresponding points, characterized by the same value of the ratio r/R 1, the gas temperature is the same.

Practically the most significant are the following

two laws of similarity:

The first law of similarity of a high-pressure unlaced arc discharge. Two high-pressure arc discharges in cylindrical tubes of different diameters (2R 1 ≠ 2R 1 "), filled with gas so that one centimeter of the length of both tubes contains the same amount of gas (g 1 = g 1 '), are similar in the case if N 1 =N 1 ', i.e. if the power consumed per unit length of the tube is the same in both cases.

The second law of similarity for a high-pressure unlaced arc discharge. Two high-pressure arc discharges in mercury vapor in cylindrical tubes of different diameters (2R 1 ≠ 2R 1 "), filled with mercury vapor so that for one centimeter of the length of each tube there are different amounts of mercury vapor (g 1 ≠g 1 ') , are similar if the powers N 1 and N 1 ' consumed per unit length of each tube satisfy the relation

N 1 /N 1 '=8.5+5.7g 1 /8.5+5.7g 1' (43)

It is assumed that the mercury in the discharge has completely passed into the vapor state. The coefficients 8.5 and 5.75 were determined experimentally.

The type of discharge described in this chapter also includes

and the positive column (flame) of the Petrov arc, representing

is a cord of isothermal plasma. In this case, the boundary

conditions on the tube walls disappear and must be replaced

conditions in the boundary layer of the cord.

Currently, in addition to the arc discharge in mercury vapor

ultra-high pressure (up to 100 atm and more), arc discharge in inert gases Ne, Ar, Kr and Xe at pressures up to 20 atm and higher has also been studied and found technical application.

INTRODUCTION.

Properties of arc discharge.

1. Arc formation.

2. Cathode spot. Appearance and individual parts

arc discharge .

3. Potential distribution and current-voltage

arc discharge characteristic .

4. Temperature and radiation of individual parts of the blowing discharge.

5. Generation of continuous oscillations using electrical

tric arc.

6. Positive arc discharge at high

and ultra-high pressure.

Application of arc discharge.

1. Modern methods of electrical processing. Among modern technological processes, one of the most common is electric welding. Welding allows you to weld, solder, glue, and spray not only metals, but also plastics, ceramics and even glass. The range of application of this method is truly immense - from the production of powerful cranes, construction metal structures, equipment for nuclear and other power plants, the construction of large-tonnage ships, nuclear icebreakers to the production of the finest microcircuits and various household products. In a number of industries, the introduction of welding has led to a radical change in technology. Thus, a real revolution in shipbuilding was the development of the continuous construction of ships from large welded sections. Many shipyards in the country are now building large-capacity all-welded tankers. Electric welding made it possible to solve the problems of creating gas pipelines designed to operate in northern conditions at a pressure of 100-120 atmospheres. Employees of the Electric Welding Institute named after. E. O. Paton was offered the original

ginal method of manufacturing pipes based on welding technology intended for such gas pipelines. Of these

pipes with walls up to 40 millimeters thick and assemble highly reliable gas pipelines crossing continents.

Soviet scientists and specialists made a great contribution to the development of electric welding. Continuing and creatively developing the legacy of his great predecessors - V. V. Petrova, N. N. Benardos, N. G. Slavyanov, they created the science of the theoretical foundations of welding technology and developed a number of new technological processes. The whole world knows the names of academicians E. O. Paton, V. P. Vologdin, K. K. Khrenov, N. N.

Rykalina and others.

Currently, electric arc, electroslag and plasma arc welding are widely used.

2. Arc welding. The simplest method is manual arc welding. The holder is connected to one pole of the current source with a flexible wire, and the product to be welded is connected to the other. A carbon or metal electrode is inserted into the holder. When the electrode briefly touches the workpiece, an arc is ignited, which melts the base metal and the electrode rod, forming a weld pool that produces a weld when solidified.

Manual arc welding requires highly qualified workers and does not have the best working conditions, but with its help you can weld parts in any spatial position, which is especially important when installing metal structures. The productivity of manual welding is relatively low and depends largely on such a simple part,

as an electrode holder. And now, like a hundred years ago,

The search for its best design continues. A series of simple and reliable electrode holders were produced by Leningrad innovators M. E. Vasiliev and V. S. Shumsky.

When arc welding, protecting the weld metal from oxygen and nitrogen in the air is of great importance. Actively interacting with the molten metal, oxygen and nitrogen in the atmospheric air form oxides and nitrides, which reduce the strength and ductility of the welded joint.

There are two ways to protect the welding site: introducing various substances into the electrode material and electrode coating (internal protection) and introducing inert gases and carbon monoxide into the welding zone, covering the welding site with fluxes (external protection).

In 1932, at the Moscow Electromechanical Institute of Railway Transport Engineers, under the leadership of Academician K.K. Khrenov, underwater electric arc welding was carried out for the first time in the world. However, back in 1856, L.I. Shpakovsky first conducted an experiment on melting copper electrodes immersed in water with an arc. On the advice of D. A. Lachinov, who received an underwater arc, N. N. Benardos in 1887 carried out underwater cutting of metal. It took 45 years to

the first experiment was scientifically substantiated and turned into a method.

And on October 16, 1969, an electric arc burst into space for the first time. This is how this outstanding event was reported in the Izvestia newspaper; “The crew of the Soyuz-6 spacecraft, consisting of Lieutenant Colonel G. S. Shonin and flight engineer V. N. Kubasov, carried out experiments on carrying out welding work in space. The purpose of these experiments was to determine the characteristics of welding various metals in outer space... Several types of automatic welding were carried out in turn.” And yes-

lee: “The experiment carried out is unique and is of great importance for science and technology in the development of technology for welding and installation work in space” ...

3. Plasma technology. This technology is based

using a high temperature arc. She

includes plasma welding, cutting, surfacing and plasma-mechanical processing.

How to improve arc performance? To do this, it is necessary to obtain an arc with a higher concentration of energy, i.e., the arc must be focused. This was achieved in 1957-1958, when at the Institute of Metallurgy. A. A. Baykov created equipment for plasma-arc cutting.

How to increase the arc temperature? Probably in the same way as they increase the pressure of a water or air stream by passing it through a narrow channel.

Passing through the narrow channel of the torch nozzle, the arc is compressed by a stream of gas (neutral, oxygen-containing) or a mixture of gases and is drawn into a thin stream. At the same time, its properties change sharply: the temperature of the arc discharge reaches

50,000 degrees, specific power reaches 500 or more kilowatts per square centimeter. The ionization of plasma in a gas column is so great that its electrical conductivity turns out to be almost the same as that of metals.

A compressed arc is called a plasma arc. With its help, plasma welding, cutting, guiding, spraying, etc. are carried out. To produce a plasma arc, special generators have been created - plasmatrons.

A plasma arc, like a regular one, can be of direct or indirect action. The direct action arc is closed on the product, the indirect action arc is closed on the second electrode, which is the nozzle. In the second case, it is not an arc that breaks out of the nozzle, but a plasma jet that arises due to heating by the arc and subsequent ionization of the plasma-forming gas. The plasma jet is mainly used for plasma spraying and processing of non-conductive materials.

The gas surrounding the arc also performs a heat-protective function.

The greatest load in a plasma torch is carried by the nozzle. The higher its heat resistance, the greater the current that can be obtained in an indirect plasmatron. The outer layer of plasma-forming gas has a relatively low temperature, so it protects the nozzle from destruction.

A significant increase in the temperature of the plasma-forming gas in direct plasma torches can lead to electrical breakdown and the occurrence of a double arc - between the cathode and the nozzle and between the nozzle and the product. In this case, the nozzle usually fails.

4. Plasma welding. There are two designs of plasmatrons. In some designs, gas is supplied along the arc, and good compression is achieved. In other designs, the gas covers the arc in a spiral, due to which it is possible to obtain a stable arc in the nozzle channel and ensure reliable protection of the nozzle by the wall layer of gas.

In direct plasma torches, the arc is not excited immediately, since the air gap between the cathode and the product is too large. First, the so-called pilot, or auxiliary, arc is excited between the cathode and the nozzle. It develops from a spark discharge, which occurs under the influence of a high-frequency voltage created by an oscillator. The gas flow blows out a pilot arc, it touches the metal being processed, and then the main arc is ignited. After this, the oscillator is turned off and the pilot arc goes out. If this does not happen, a double arc may occur.

The weld area during plasma welding, as with other types of welding, is protected from the action of ambient air. To do this, in addition to the plasma-forming gas, a protective gas is supplied into a special nozzle: argon or cheaper and more common carbon dioxide. Carbon dioxide is often used not only for protection, but also for plasma formation. Sometimes plasma welding is carried out under a layer of flux.

Plasma arc welding can be performed either automatically or manually. Currently, this method has become quite widespread. Many factories have introduced plasma welding of aluminum alloys and steels. Significant savings resulted from the use of single-pass plasma welding of aluminum instead of multi-pass argon-arc welding.

ki. Welding is carried out in an automatic installation using carbon dioxide as a plasma-forming and protective agent.

In modern life, the use of electrical energy has become widespread. Achievements of electrical engineering are used in all spheres of practical human activity: in industry, agriculture, transport, medicine, everyday life, etc. Advances in electrical engineering have a significant impact on the development of radio engineering, electronics, telemechanics, automation, computer technology -nicks, cybernetics. All this became possible as a result of the construction of powerful power plants, electrical networks, the creation of new electrical power systems, and the improvement of electrical devices. The modern electrical industry produces machines and devices for the production, transmission, conversion, distribution and consumption of electricity, a variety of electrical equipment and technological equipment, electrical measuring instruments and telecommunications, regulating, monitoring and control equipment for automatic control systems, medical and scientific equipment, electrical appliances and machines and much more. In recent years, various methods of electrical processing have received further development: electric welding, plasma cutting and surfacing of metals, plasma-mechanical and electrical discharge processing. From the above

It is clear that the study of discharge in gas is of great importance for general scientific and technical progress. Therefore, there is no need to stop there, but it is necessary to continue research, looking for the unknown, thereby further stimulating the construction of new theories.

Khabarovsk State Pedagogical University

COURSE WORK

"ARC DISCHARGE IN GASES"

Completed by: student 131gr. FMF

Zyulyev M. N.

The luminous current channel of this discharge was arced, which gave rise to the name D. r.

Formation of D. r. preceded by a short non-stationary process in the space between the electrodes - the discharge gap. The duration of this process (time of establishment of D. r.) is usually Arc discharge 10 -6 -10 -4 sec depending on the pressure and type of gas, the length of the discharge gap, the condition of the electrode surfaces, etc. D. r. obtained by ionizing gas in the discharge gap (for example, using an auxiliary, so-called ignition electrode). In other cases, to obtain D. r. heat one or both electrodes to a high temperature or move the closed ones apart short time electrodes. D. r. may also arise as a result of breakdown of the electrical (See Electrical breakdown) discharge gap during a short-term sharp increase in voltage between the electrodes. If breakdown occurs at gas pressure close to atmospheric, then non-stationary process The preceding discharge is the spark discharge.

Typical parameters of D. r. For D. r. characterized by an extreme variety of forms it takes: it can occur at almost any gas pressure - from less than 10 -5 mmHg Art. up to hundreds atm; potential difference between electrodes D. r. can take values ​​from several volts to several thousand volts (high-voltage D. r.). D. r. can occur not only at constant, but also at alternating voltage between the electrodes. However, the half-cycle of an alternating voltage is usually much longer than the time it takes to establish the voltage, which makes it possible to consider each electrode as a cathode during one half-cycle, and as an anode in the next half-cycle. Distinctive Features all forms of D. r. (closely related to the nature of the emission of electrons from the cathode in this type of discharge) are the small value of the cathode drop (See Cathode drop) and the high current density at the cathode. Cathode drop in D. r. usually on the order of the ionization potential (See Ionization potential) of the working gas or even lower (1-10 V); The current density at the cathode is 10 2 -10 7 a/cm 2. With such a high current density, the current strength in the D. r. usually also large - about 1-10 a and higher, and in some forms of D. r. reaches many hundreds and thousands of amperes. However, there are also D. r. with a low current intensity (for example, a D. R. with a mercury cathode can burn at currents of 0.1 a and below).

Electronic emission in D. rub. The fundamental difference between D. r. from other types of stationary electrical discharge in gas lies in the nature of the elementary processes occurring at the cathode and in the near-cathode region. If in a glow discharge (See Glow discharge) and a negative corona discharge (See Corona discharge) secondary electron emission occurs, then in D. r. electrons fly out of the cathode in the processes of thermionic emission (See Thermionic emission) and field emission (also called tunnel emission (See Tunnel emission)). When in D. r. Only the first of these processes occurs; it is called thermionic. The intensity of thermionic emission is determined by the temperature of the cathode; therefore, for the existence of thermionic D. r. it is necessary that the cathode or its individual sections be heated to a high temperature. Such heating is carried out by connecting the cathode to an auxiliary energy source (Dr. with external heating; D.r. with artificial heating). Thermionic D. r. It also occurs when the temperature of the cathode is sufficiently increased by the impacts of positive ions formed in the discharge gap and accelerated by the electric field towards the cathode. However, more often with D. r. Without artificial heating, the intensity of thermionic emission is too low to maintain the discharge, and the process of field emission plays a significant role. The combination of these two types of emission is called thermal field emission.

Field emission from the cathode requires the existence of a strong electric field at its surface. Such a field in D. r. is created by a volume charge of positive ions removed from the cathode at a distance on the order of the mean free path (See Mean free path) of these ions (10 -6 -10 -4 cm). Calculations show that field emission cannot independently support the D. r. and is always, to one degree or another, accompanied by thermionic emission. Due to the difficulty of studying processes in a thin near-cathode layer at high current densities, experimental data on the role of field emission in D.R. Not enough has been accumulated yet. Theoretical analysis cannot yet satisfactorily explain all the phenomena observed in various forms of D. r.

The relationship between the characteristics of D. r. and emission processes. The layer in which the electric field arises, causing field emission, is so thin that it does not create a large drop in the potential difference at the cathode. However, in order for this field to be strong enough, the volume charge density of the ions at the cathode, and therefore the ion current density, must be high. Thermionic emission can also occur at low kinetic energy of ions at the cathode (i.e., at a low cathode incidence), but under these conditions it requires a high current density - the cathode heats up the more, the greater the number of ions bombarding it. That., distinctive features D. r. (small cathode drop and high current density) are due to the nature of near-cathode processes.

Plasma D. r. Discharge gap D. r. filled by plasma, consisting of electrons, ions, neutral and excited atoms and molecules of the working gas and electrode substance. Average energies of particles of different types in plasma D. r. may be different. Therefore, when talking about the temperature of a electron, a distinction is made between the ionic temperature, the electron temperature, and the temperature of the neutral component. If these temperatures are equal, the plasma is called isothermal.

Dependent D. r. D. r. is called dependent. with artificial heating of the cathode, since such a discharge cannot be maintained using its own energy: when turned off external source it goes out when incandescent. The discharge is easily ignited without auxiliary ignition electrodes. Increasing the voltage of such a D. r. first, it amplifies its current to a value determined by the intensity of thermionic emission from the cathode at a given filament temperature. Then, up to a certain critical voltage, the current remains almost constant (the so-called free mode). When the voltage exceeds the critical voltage, the nature of the emission from the cathode changes: the Photoelectric effect and secondary electron emission begin to play a significant role in it (the energy of positive ions becomes sufficient to knock electrons out of the cathode). This leads to a sharp increase in the discharge current - it goes into a captive mode.

Under certain conditions, D. r. with artificial heating continues to burn steadily when the voltage between the electrodes is reduced to values ​​less than not only the ionization potential of the working gas, but also its lowest excitation potential. This form of D. r. called low voltage arc. Its existence is due to the appearance near the cathode of a maximum potential that exceeds the potential of the anode and is close to the first excitation potential of the gas, as a result of which stepwise ionization becomes possible (see Ionization).

Independent D. r. Maintaining such D. r. is carried out due to the energy of the discharge itself. On refractory cathodes (tungsten, molybdenum, graphite) independent D. r. is purely thermionic in nature - bombardment with positive ions heats the cathode to a very high temperature. The substance of the low-melting cathode intensively evaporates during D. r.; evaporation cools the cathode, and its temperature does not reach values ​​at which the discharge can be supported by thermionic emission alone - along with it, field emission occurs.

Independent D. r. can exist both at extremely low gas pressures (so-called vacuum arcs) and at high pressures. Plasma of independent D. r. low pressure is characterized by non-isothermality: the ion temperature only slightly exceeds the temperature of the neutral gas in the space surrounding the discharge region, while the electron temperature reaches tens of thousands of degrees, and in narrow tubes and at high currents - hundreds of thousands. This is explained by the fact that more mobile electrons, receiving energy from the electric field, do not have time to transfer it to heavy particles in rare collisions.

In D. r. high pressure plasma is isothermal (more precisely, quasi-isothermal, because, although the temperatures of all components are equal, the temperature in different parts of the plasma column is not the same). This form of D. r. characterized by significant current strength (from 10 to 10 3 A) and high plasma temperature (about 10 4 TO). Highest temperatures in such a D. r. are achieved by cooling the arc with a flow of liquid or gas - the current channel of the “cooled arc” becomes thinner and, at the same current value, heats up more. It is this form of D. r. called an electric arc - under the influence of externally directed or convection gas flows caused by the discharge itself, the current channel of the D. r. bends.

Cathode spots. Independent D. r. What distinguishes low-melting cathodes is that thermal autoemission of electrons occurs in it only from small areas of the cathode - the so-called cathode spots. The small sizes of these spots (less than 10 -2 cm) are caused by the pinch effect - contraction of the current channel by its own magnetic field. The current density in the cathode spot depends on the cathode material and can reach tens of thousands a/cm 2. Therefore, intense erosion occurs in the cathode spots - jets of vapor of the cathode substance fly out from them at a speed of the order of 10 6 cm/sec. Cathode spots also form during D. r. on refractory cathodes, if the working gas pressure is less than approximately 10 2 mmHg Art. At higher pressures, thermal field emission D. r. with cathode spots moving chaotically along the cathode, it transforms into thermionic radiation. without cathode spot.

Applications of D. r. D. r. widely used in arc furnaces (See Arc furnace) for smelting metals, in gas-discharge light sources (See), in electric welding (See Electric welding), and serves as a source of plasma in Plasmatrons. Various forms of D. r. occur in gas-filled and vacuum electric current converters (mercury current rectifiers (See Current Rectifier), gas and vacuum electric switches (See Electric Switch), etc.). D. r. with artificial heating of the cathode is used in fluorescent lamps (See Fluorescent lamp), Gazotron ah, Thyratron ah, ion sources and sources of electron beams.

Lit.: Electric current in gas. Steady current, M., 1971; Kesaev I.G., Cathode processes of the electric arc, M., 1968; Finkelnburg V., Mecker G., Electric arcs and thermal plasma, trans. from German, M., 1961; Engel A., Ionized gases, trans. from English, M., 1959; Kaptsov N. A., Electrical phenomena in gases and vacuum, M.-L., 1947.

A.K. Musin.

Big Soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

arc discharge- arc discharge; industry arc-shaped discharge; voltaic arc An electric discharge in which the electric field in the discharge gap is determined mainly by the magnitude and location of space charges in it, characterized by a small cathode ... ... Polytechnic terminological explanatory dictionary

Electric discharge in gases, characterized by a high current density and a small potential drop near the cathode. Supported by thermionic emission or field emission from the cathode. Gas temperature in the arc discharge channel at... ... Big Encyclopedic Dictionary

ARC DISCHARGE- one of the types of independent electrical discharge in gas, characterized by high density current Ionized gas heated to a high temperature in a column between the electrodes to which electrical voltage, is located in... ... Big Polytechnic Encyclopedia

arc discharge- lankinis išlydis statusas T sritis fizika atitikmenys: engl. arc discharge; electric arc in gas vok. Bogenentladung, f rus. arc discharge, m; arc discharge in gas, m pranc. décharge d'arc, f; décharge en régime d'arc, f; décharge par arc, f … Fizikos terminų žodynas

Electric discharge in gases, burning at almost any gas pressure exceeding 10 2 10 3 mm Hg. Art.; characterized by a high current density at the cathode and a small potential drop. First observed in 1802 by V.V. Petrov in the air... ... Encyclopedic Dictionary

Electric arc in the air Electric arc physical phenomenon, one of the types of electrical discharge in gas. Synonyms: Voltaic arc, Arc discharge. It was first described in 1802 by the Russian scientist V.V. Petrov. An electric arc is... ... Wikipedia

arc discharge- lankinis išlydis statusas T sritis automatika atitikmenys: engl. arc discharge vok. Bogenentladung, f; Lichtbogenentladung, f rus. arc discharge, m pranc. décharge d arc, f; décharge en arc, f … Automatikos terminų žodynas

arc discharge- lankinis išlydis statusas T sritis chemija apibrėžtis Savaiminio elektros išlydžio dujose rūšis. atitikmenys: engl. arc discharge rus. arc discharge... Chemijos terminų aiškinamasis žodynas