arches 

§92. Electric arc and methods of its extinguishing. Arc. Conditions for the initiation and burning of an arc. Arc quenching methods Electric arc resistance

An electric arc is an arc discharge that occurs between two electrodes, or an electrode and a workpiece, and which allows two or more parts to be joined by welding.

The welding arc, depending on the environment in which it occurs, is divided into several groups. It can be open, closed, and also in the environment of protective gases.

An open arc flows in the open air through the ionization of particles in the combustion area, as well as due to metal vapors of the welded parts and electrode material. The closed arc, in turn, burns under the flux layer. This allows you to change the composition of the gaseous medium in the combustion area and protect the metal of the workpieces from oxidation. In this case, the electric arc flows through metal vapors and ions of the flux additive. The arc that burns in a protective gas environment flows through the ions of this gas and metal vapor. This also helps to prevent oxidation of parts, and, consequently, to increase the reliability of the formed connection.

The electric arc differs in the type of current supplied - alternating or constant - and in the duration of burning - pulsed or stationary. In addition, the arc may have direct or reverse polarity.

According to the type of electrode used, non-consumable and consumable electrodes are distinguished. The use of one or another electrode directly depends on the characteristics that the welding machine. The arc that occurs when using a non-consumable electrode, as the name implies, does not deform it. When welding with a consumable electrode, the arc current melts the material and it is deposited on the original workpiece.

The arc gap can be conditionally divided into three characteristic sections: cathode, anode, and the arc shaft. In this case, the last section, i.e. the arc trunk has the greatest length, however, the characteristics of the arc, as well as the possibility of its occurrence, are determined precisely by the near-electrode regions.

In general, the characteristics that an electric arc has can be combined into the following list:

1. Arc length. This refers to the total distance of the cathode and anode regions, as well as the arc shaft.

2. Arc voltage. It consists of the sum on each of the areas: trunk, near-cathode and near-anode. In this case, the change in voltage in the near-electrode regions is much larger than in the remaining region.

3. Temperature. An electric arc, depending on the composition of the gaseous medium, the material of the electrodes, can develop temperatures up to 12 thousand degrees Kelvin. However, such peaks are not located over the entire plane of the electrode end face. Since even with the best processing, there are various irregularities and bumps on the material of the conductive part, due to which many discharges occur, which are perceived as one. Of course, the temperature of the arc largely depends on the environment in which it burns, as well as on the parameters of the supplied current. For example, if you increase the current value, then, accordingly, the temperature value will also increase.

And, finally, the current-voltage characteristic or VAC. It represents the dependence of voltage on the length and magnitude of the current.

When switching electrical appliances or overvoltages in the circuit between the current-carrying parts, an electric arc may appear. It can be used for useful technological purposes and at the same time be harmful to the equipment. Currently, engineers have developed a number of methods for combating and using the electric arc for useful purposes. In this article, we will look at how it occurs, its consequences, and its scope.

Arc formation, its structure and properties

Imagine we are doing an experiment in a laboratory. We have two conductors, for example, metal nails. We place them with a tip to each other at a short distance and connect the leads of an adjustable voltage source to the nails. If you gradually increase the voltage of the power source, then at a certain value we will see sparks, after which a steady glow similar to lightning is formed.

Thus, the process of its formation can be observed. The glow that forms between the electrodes is plasma. In fact, this is an electric arc or flow electric current through the gaseous medium between the electrodes. In the figure below you see its structure and current-voltage characteristic:

And here are the approximate temperatures:

Why does an electric arc occur?

Everything is very simple, we considered in the article about, as well as in the article about, that if any conductive body (steel nail, for example) is introduced into electric field- Charges will begin to accumulate on its surface. Moreover, the smaller the bending radius of the surface, the more they accumulate. In simple terms, the charges accumulate on the tip of the nail.

Between our electrodes, the air is a gas. Under the action of an electric field, it ionizes. As a result of all this, conditions arise for the formation of an electric arc.

The voltage at which an arc occurs depends on the specific medium and its condition: pressure, temperature and other factors.

Interesting: according to one version, this phenomenon is so called because of its shape. The fact is that in the process of burning the discharge, the air or other gas surrounding it heats up and rises, as a result of which a rectilinear shape is distorted and we see an arc or arch.

To ignite the arc, it is necessary either to overcome the breakdown voltage of the medium between the electrodes, or to break the electrical circuit. If there is a large inductance in the circuit, then, according to the laws of commutation, the current in it cannot be interrupted instantly, it will continue to flow. In this regard, the voltage between the disconnected contacts will increase, and the arc will burn until the voltage disappears and the energy accumulated in the magnetic field of the inductor dissipates.

Consider the conditions of ignition and combustion:

There must be air or other gas between the electrodes. To overcome the breakdown voltage of the medium, a high voltage of tens of thousands of volts is required - this depends on the distance between the electrodes and other factors. To maintain the arc, 50-60 volts and a current of 10 or more amperes are sufficient. Specific values ​​depend on the environment, the shape of the electrodes and the distance between them.

Harm and fight against it

We examined the causes of the occurrence of an electric arc, now let's figure out what harm it does and how to extinguish it. The electric arc damages the switching equipment. Have you noticed that if you turn on a powerful electrical appliance in the network and after a while pull the plug out of the socket, a small flash occurs. This arc is formed between the contacts of the plug and the socket as a result of a break in the electrical circuit.

Important! During the burning of an electric arc, a lot of heat is released, the temperature of its burning reaches values ​​of more than 3000 degrees Celsius. In high-voltage circuits, the arc length reaches a meter or more. There is a danger of both harm to human health and the condition of the equipment.

The same thing happens in light switches, other switching equipment, including:

  • automatic switches;
  • magnetic starters;
  • contactors and more.

In devices that are used in 0.4 kV networks, including the usual 220 V, they use special means protection - arc chutes. They are needed to reduce the harm caused to contacts.

In general, the arc chute is a set of conductive partitions of a special configuration and shape, fastened with walls of dielectric material.

When the contacts are opened, the formed plasma bends towards the arc extinguishing chamber, where it is separated into small sections. As a result, it cools down and extinguishes.

In high-voltage networks, oil, vacuum, gas circuit breakers are used. In an oil circuit breaker, damping occurs by switching contacts in an oil bath. When an electric arc burns in oil, it decomposes into hydrogen and gases. A gas bubble is formed around the contacts, which tends to escape from the chamber at high speed and the arc cools down, since hydrogen has good thermal conductivity.

Vacuum circuit breakers do not ionize gases and there are no conditions for arcing. There are also circuit breakers filled with gas under high pressure. When an electric arc is formed, the temperature in them does not rise, the pressure rises, and because of this, the ionization of gases decreases or deionization occurs. They are considered a promising direction.

Switching at zero AC is also possible.

Useful application

The considered phenomenon has also found a number of useful applications, For example:


Now you know what an electric arc is, what causes this phenomenon and possible applications. We hope that the information provided was clear and useful for you!

materials

The opening of an electrical circuit at significant currents and voltages, as a rule, is accompanied by an electric discharge between divergent contacts. When the contacts diverge, the transition resistance of the contact and the current density in the last contact area increase sharply. The contacts are heated to melting, and a contact isthmus is formed from the molten metal, which, with further divergence of the contacts, breaks, and the metal of the contacts evaporates. The air gap between the contacts ionizes and becomes conductive, and an electric arc appears in it under the action of high voltage arising from the laws of switching.

The electric arc contributes to the destruction of contacts and reduces the speed of the switching device, since the current in the circuit does not drop to zero instantly. The occurrence of an arc can be prevented by increasing the resistance of the circuit in which the contacts open, by increasing the distance between the contacts, or by using special arc extinguishing measures.

The product of the limiting values ​​​​of voltage and current in the circuit, at which an electric arc does not occur with a minimum distance between the contacts, is called the breaking or switching power of the contacts. As the voltage in the circuit increases, the limiting switched current has to be limited. The switching power also depends on the time constant of the circuit: the more
the less power the contacts can switch. In AC circuits, the electric arc goes out at the moment when the instantaneous value of the current is zero. The arc may reappear in the next half-cycle if the voltage across the contacts rises faster than the dielectric strength of the gap between the contacts is restored. However, in all cases, the arc in the AC circuit is less stable, and the breaking power of the contacts is several times higher than in the circuit. direct current. On the contacts of low-power electrical devices, an electric arc rarely appears, but sparking is often observed - a breakdown of the insulating gap formed during the rapid opening of contacts in low-current circuits. This is especially dangerous in sensitive and high-speed devices (relays), in which the distance between the contacts is very small. Sparking shortens the life of the contacts and can lead to false alarms. To reduce sparking at the contacts, special spark extinguishing devices are used.

Arc and spark extinguishing device.

The most effective way to extinguish an electric arc is to cool it by moving in the air, contacting the insulating walls of special chambers, which take away the heat of the arc.

In modern devices, arc chutes with a narrow slot and magnetic blast are widely used. The arc can be thought of as a current-carrying conductor; if it is placed in a magnetic field, then a force will arise that will cause the arc to move. During its movement, the arc is blown by air; falling into a narrow gap between two insulating plates, it deforms and, due to an increase in pressure in the chamber gap, goes out (Fig. 21).

Rice. 21. The device of the arc extinguishing chamber with a narrow gap

The slit chamber is formed by two walls 1 made of insulating material. The gap between the walls is very small. Coil 4, connected in series with the main contacts 3, excites the magnetic flux
which is directed by ferromagnetic tips 2 into the space between the contacts. As a result of the interaction of the arc and the magnetic field, a force appears
displacing the arc to the plates 1. This force is called the Lorentz force, which is defined as:

where - particle charge [Coulomb],

‑velocity of a charged particle in the field [m/s],

‑force acting on a charged particle [Newtons],

‑angle between the velocity vector and the magnetic induction vector.

We can say that the speed of a particle in a conductor is:
where - the length of the conductor (arc), and - the time of passage of a charged particle along the arc. In turn, the current is the number of charged particles per second through the cross section of the conductor
. That is, you can write:

where - current in the conductor (arc) [Amperes],

-length of conductor (arc) [meters],

- magnetic field induction [Tesla],

‑force acting on the conductor (arc) [Newtons],

‑angle between the current vector and the magnetic induction vector.

The direction of force corresponds to the left hand rule: magnetic lines of force rest against the palm, straightened four fingers are located in the direction of the current the bent thumb shows the direction of the electromagnetic force
. The described action of the magnetic field (induction ) is called electromechanical or power, and the resulting expression is the law of electromagnetic forces.

This design of the arc chute is also used on alternating current, since with a change in the direction of the current, the direction of the flow changes
and the direction of the force
remains unchanged.

To reduce sparking on low-power DC contacts, a diode is connected in parallel with the load device (Fig. 22).

Rice. 22. Turning on a diode to reduce sparking

In this case, the circuit after switching (after switching off the source) closes through the diode, thus reducing the energy of sparking.

Physical basis of arc burning. When the contacts of an electrical apparatus are opened, an electric arc occurs due to the ionization of the space between them. At the same time, the gap between the contacts remains conductive and the passage of current through the circuit does not stop.

For ionization and arc formation, it is necessary that the voltage between the contacts is approximately 15-30 V and the circuit current is 80-100 mA.

When the space between the contacts is ionized, the gas (air) atoms filling it decay into charged particles - electrons and positive ions. The flow of electrons emitted from the surface of a contact under a negative potential (cathode) moves towards a positively charged contact (anode); the flow of positive ions moves towards the cathode (Fig. 303a).

The main current carriers in the arc are electrons, since positive ions, having a large mass, move much more slowly than electrons and therefore carry much less electric charges per unit time. However, positive ions play an important role in the arcing process. Approaching the cathode, they create a strong electric field near it, which affects the electrons present in the metal cathode and pull them out from its surface. This phenomenon is called field emission (Fig. 303b). In addition, positive ions continuously bombard the cathode and give it their energy, which turns into heat; in this case, the cathode temperature reaches 3000-5000 °C.

With an increase in temperature, the movement of electrons in the cathode metal accelerates, they acquire more energy and begin to leave the cathode, flying out into the environment. This phenomenon is called thermionic emission. Thus, under the action of auto- and thermionic emission, more and more electrons enter the electric arc from the cathode.

When moving from the cathode to the anode, the electrons, colliding on their way with neutral gas atoms, split them into electrons and positive ions (Fig. 303, c). This process is called impact ionization. The new, so-called secondary electrons that appeared as a result of impact ionization begin to move towards the anode and, during their movement, split more and more new gas atoms. The considered process of gas ionization has an avalanche-like character, just as one stone thrown from a mountain captures more and more stones on its way, generating an avalanche. As a result, the gap between the two contacts is filled with a large number of electrons and positive ions. This mixture of electrons and positive ions is called plasma. Thermal ionization plays a significant role in the formation of plasma, which occurs as a result of an increase in temperature, which causes an increase in the speed of movement of charged gas particles.

The electrons, ions, and neutral atoms that make up the plasma continuously collide with each other and exchange energy; in this case, some atoms under the impact of electrons come into an excited state and emit an excess of energy in the form of light radiation. However, the electric field acting between the contacts causes the bulk of the positive ions to move towards the cathode, and the bulk of the electrons towards the anode.

In a DC electric arc in steady state, thermal ionization is decisive. In an alternating current arc, when the current passes through zero, impact ionization plays a significant role, and during the rest of the arc burning time, thermal ionization plays an important role.

When the arc burns, simultaneously with the ionization of the gap between the contacts, the reverse process occurs. Positive ions and electrons, interacting with each other in the intercontact space or when they hit the walls of the chamber in which the arc burns, form neutral atoms. This process is called recombination; upon termination of ionization recombination leads to the disappearance of electronosis and ions from the interelectrode space - it is deionized. If recombination takes place on the chamber wall, then it is accompanied by the release of energy in the form of heat; during recombination in the interelectrode space, energy is released in the form of radiation.

When in contact with the walls of the chamber in which the contacts are located, the arc is cooled, which. leads to increased deionization. Deionization also occurs as a result of the movement of charged particles from the central regions of the arc with a higher concentration to the peripheral regions with a lower concentration. This process is called diffusion of electrons and positive ions.

The arc burning zone is conditionally divided into three sections: the cathode zone, the arc shaft and the anode zone. In the cathode zone, intense electron emission from the negative contact occurs, the voltage drop in this zone is about 10 V.

Plasma is formed in the arc shaft with approximately the same concentration of electrons and positive ions. Therefore, at each moment of time, the total charge of the positive ions of the plasma compensates for the total negative charge of its electrons. The high concentration of charged particles in the plasma and the absence of an electric charge in it determine the high electrical conductivity of the arc shaft, which is close to the electrical conductivity of metals. The voltage drop in the arc shaft is approximately proportional to its length. The anode zone is filled mainly with electrons coming from the arc shaft to the positive contact. The voltage drop in this zone depends on the current in the arc and the size of the positive contact. The total voltage drop in the arc is 15-30 V.

The dependence of the voltage drop U dg acting between the contacts on the current I passing through the electric arc is called the current-voltage characteristic of the arc (Fig. 304, a). The voltage U c, at which it is possible to ignite the arc at a current I \u003d 0, is called ignition voltage. The value of the ignition voltage is determined by the material of the contacts, the distance between them, temperature and environment. After the occurrence

electric arc, its current increases to a value close to the load current that flowed through the contacts before the trip. In this case, the resistance of the contact gap drops faster than the current increases, which leads to a decrease in the voltage drop U dg. The arc burning mode corresponding to curve a is called static.

When the current drops to zero, the process corresponds to curve b and the arc stops at a lower voltage drop than the ignition voltage. The voltage U g, at which the arc goes out, is called extinguishing voltage. It is always less than the ignition voltage due to an increase in the temperature of the contacts and an increase in the conductivity of the intercontact gap. The greater the rate of current decline, the lower the arc quenching voltage at the moment of current termination. The volt-ampere characteristics b and c correspond to a decrease in current at different rates (for curve c more than for curve b), and straight line d corresponds to an almost instantaneous decrease in current. Such a character of current-voltage characteristics is explained by the fact that with a rapid change in current, the ionization state of the intercontact gap does not have time to follow the change in current. It takes a certain time to deionize the gap, and therefore, despite the fact that the current in the arc has fallen, the conductivity of the gap has remained the same, corresponding to a large current.

The volt-ampere characteristics b - d, obtained with a rapid change in current to zero, are called dynamic. For each intercontact gap, electrode material and medium, there is one static characteristic of the arc and many dynamic ones enclosed between curves a and d.

When burning an AC arc during each half-cycle, the same physical processes take place as in a DC arc. At the beginning of the half-cycle, the voltage on the arc increases according to a sinusoidal law to the value of the ignition voltage U c - section 0-a (Fig. 304, b), and then after the onset of the arc it drops as the current increases - section a - b. In the second part of the half-cycle, when the current begins to decrease, the arc voltage again increases to the value of the quenching voltage U g when the current drops to zero - section b - c.

During the next half-cycle, the voltage changes sign and, according to a sinusoidal law, increases to the value of the ignition voltage corresponding to point a’ of the current-voltage characteristic. As the current increases, the voltage decreases and then rises again as the current decreases. The arc voltage curve, as seen in fig. 304, b, has the shape of a cut sinusoid. The process of deionization of charged particles in the gap between the contacts continues only an insignificant fraction of the period (sections 0 - a and c - a ') and, as a rule, does not end during this time, as a result of which the arc reappears. The final extinction of the arc will take place only after a series of re-ignitions during one of the subsequent zero crossings of the current.

The resumption of the arc after the current passes through zero is explained by the fact that after the current drops to zero, the ionization existing in the arc shaft does not disappear immediately, since it depends on the plasma temperature in the residual arc shaft. As the temperature decreases, the electrical strength of the intercontact gap increases. However, if at some point in time the instantaneous value of the applied voltage is greater than the breakdown voltage of the gap, then its breakdown will occur, an arc will occur and a current of a different polarity will flow.

Arc quenching conditions. The conditions for extinguishing a DC arc depend not only on its current-voltage characteristic, but also on the parameters of the electrical circuit (voltage, current, resistance and inductance), which are turned on and off by the contacts of the device. On fig. 305, and the current-voltage characteristic of the arc is shown

(curve 1) and the dependence of the voltage drop across the resistor R included in this circuit (straight line 2). In steady state, the voltage U and the current source is equal to the sum of the voltage drops in the arc U dg and IR across the resistor R. When the current in the circuit changes, e is added to them. d.s. self-induction ±e L (shown as shaded ordinates). Long burning arcing is possible only in modes corresponding to points A and B, when the voltage U and - IR applied to the gap between the contacts is equal to the voltage drop U dg. In this case, in the mode corresponding to point A, the arc burning is unstable. If, for some reason, the current increased during the arcing at this point of the characteristic, then the voltage U dg will become less than the applied voltage U and - IR. An excess of applied voltage will cause an increase in current, which will increase until it reaches the value of Iv.

If, in the mode corresponding to point A, the current decreases, the applied voltage U and - IR will become less than U dg and the current will continue to decrease until the arc goes out. In the mode corresponding to point B, the arc burns steadily. With an increase in current over I v, the voltage drop in the arc U dg will become greater than the applied voltage U and - IR and the current will begin to decrease. When the current in the circuit becomes less than I v, the applied voltage U and - IR will become greater than U dg and the current will begin to increase.

Obviously, in order to ensure the extinction of the arc in the entire given range of current change I from the greatest value to zero when the circuit is turned off, it is necessary that the current-voltage characteristic 1 be located above the straight line 2 for the circuit to be turned off (Fig. 305, b). Under this condition, the voltage drop in the arc U dg will always be greater than the voltage applied to it U and - IR and the current in the circuit will decrease.

The main means of increasing the voltage drop in the arc is to increase the length of the arc. When opening low-voltage circuits with relatively small currents, quenching is ensured by an appropriate choice of contact solution, between which an arc occurs. In this case, the arc goes out without any additional devices.

For contacts that break power circuits, the length of the arc required for extinguishing is so large that it is no longer possible to implement such a contact solution in practice. In such electrical apparatus, special arc extinguishing devices are installed.

Extinguishing devices. Arc quenching methods can be different, but they are all based on following principles: forced lengthening of the arc; cooling the intercontact gap by means of air, vapors or gases; division of the arc into a number of separate short arcs.

When the arc lengthens and moves away from the contacts, the voltage drop in the arc column increases and the voltage applied to the contacts becomes insufficient to maintain the arc.

Cooling of the intercontact gap causes increased heat transfer from the arc column to the surrounding space, as a result of which charged particles, moving from the inside of the arc to its surface, accelerate the deionization process.

The division of the arc into a number of separate short arcs leads to an increase in the total voltage drop in them, and the voltage applied to the contacts becomes insufficient to sustain the arc, so it is extinguished.

The principle of extinguishing by lengthening the arc is used in devices with protective horns and in knife switches. The electric arc that occurs between contacts 1 and 2 (Fig. 306, a) when they open, rises under the action of the force F B created by the flow of air heated by it, stretches and lengthens on the divergent fixed horns, which leads to its extinction. The lengthening and extinguishing of the arc is also facilitated by the electrodynamic force created as a result of the interaction of the arc current with the magnetic field that arises around it. In this case, the arc behaves like a current-carrying conductor in a magnetic field (Fig. 307, a), which, as was shown in Chapter III, tends to push it out of the field.

To increase the electrodynamic force F e acting on the arc, in some cases, a special arc extinguishing coil 2 (Fig. 307, b) is included in the circuit of one of the contacts 1 (Fig. 307, b), which creates a strong magnetic field in the arcing zone, magnetic

the filament flow of which F, interacting with the current I of the arc, provides intensive blowing and extinguishing of the arc. The rapid movement of the arc along the horns 3, 4 causes its intense cooling, which also contributes to its deionization in the chamber 5 and extinguishing.

Some devices use methods of forced cooling and stretching the arc with compressed air or other gas.

When contacts 1 and 2 open (see Fig. 306, b), the resulting arc is cooled and blown out of the contact zone by a jet compressed air or gas with FB power.

An effective means of cooling the electric arc with its subsequent extinguishing are arc chutes. various designs(Fig. 308). The electric arc, under the influence of a magnetic field, air flow, or by other means, is driven into narrow slots or a labyrinth of the chamber (Fig. 308, a and b), where it is in close contact with its walls 1, partitions 2, gives them heat and goes out. Wide application in electrical devices e. p.s. they find labyrinth-slotted chambers, where the arc is lengthened not only by stretching between the contacts, but also by its zigzag curvature between the chamber partitions (Fig. 308, c). The narrow gap 3 between the chamber walls contributes to the cooling and deionization of the arc.

The arc quenching devices, the action of which is based on the division of the arc into a series of short arcs, include a deionic grid (Fig. 309, a), built into the arc chute.

The deion grating is a set of a number of individual steel plates 3 isolated from each other. The electric arc that has arisen between opening contacts 1 and 2 is divided by the grid into a number of shorter arcs connected in series. To maintain the burning of the arc without its division, a voltage U is required, equal to the sum of the near-electrode (anode and cathode) voltage drop U e and the voltage drop in the arc column U st.

When one arc is divided into n short arcs, the total voltage drop in the column of all short arcs will still be equal to nU e, as in one common arc, but the total near-electrode voltage drop in all arcs will be equal to nU e. Therefore, to maintain the arc in this case, a voltage is required

U \u003d nU e + U st.

The number of arcs n is equal to the number of lattice plates and can be chosen such that the possibility of stable arc burning at a given voltage U is completely excluded. The action of such a damping principle is effective both with direct and alternating current. When the alternating current passes through zero, a voltage of 150–250 V is required to maintain the arc. In this regard, the number of plates can be chosen to be much smaller than with direct current.

AT fuses with a filler during the melting of the insert and the occurrence of an electric arc due to high blood pressure gases in the cartridge, ionized particles move in the transverse direction. At the same time, they fall between the aggregate grains, cool down and deionize. Filler grains, moving under the action of excess pressure, break the arc into big number microarcs, which ensures their quenching.

In fuses without filler, the body is often made of a material that releases gas abundantly when heated. Such materials include, for example, fiber. When in contact with the arc, the body heats up and releases gas, which contributes to extinguishing the arc. Similarly, the arc is extinguished in oil circuit breakers of alternating current (Fig. 309, b), with the only difference being that non-combustible oil is used here instead of dry filler. When an arc occurs at the moment of opening of the movable 1, 3 and fixed 2 contacts, its extinguishing occurs under the action of two factors: a large number hydrogen, which does not support combustion (in the oil used for this purpose, the hydrogen content is 70-75%), and intensive cooling of the arc by oil due to its high heat capacity. The arc goes out at the moment when the current is zero. Oil not only contributes to the accelerated extinction of the arc, but also serves as an insulation for current-carrying and grounded parts of the structure. Oil is not used to extinguish an arc in a DC circuit, since under the influence of an arc it quickly decomposes and loses its insulating qualities.

In modern electrical apparatus, arc extinguishing is often carried out by combining two or more of the considered

above methods (for example, using an arc chute, protective horns and a deion grid).

The conditions for extinguishing the electric arc determine the breaking capacity of protective devices. It is characterized by the highest current that can trip the device with a certain arc quenching time.

In the event of a short circuit in an electrical circuit connected to a source of electrical energy, the current in the circuit increases along curve 1 (Fig. 310). At the moment t 1 when it reaches the value to which it is adjusted protective apparatus(setting current I y), the device trips and disconnects the protected circuit, as a result of which the current decreases along curve 2.

The time counted from the moment the signal is given to turn off (or turn on) the device until the moment the opening (or closing) of the contacts begins is called the device’s own response time t s. When disconnected, the moment of the beginning of the opening of the contacts corresponds to the occurrence of an arc between the divergent contacts. AT circuit breakers this time is measured from the moment the current reaches the setting value t 1 until the moment the arc appears between the contacts t 2 . Arc burning time t dg is the time from the moment the arc appears t 2 until the moment the passage of current t 3 stops. Full time shutdown t p is the sum of the own time and the arc burning time.

Hello to all visitors to my blog. The topic of today's article is an electric arc and protection against an electric arc. The topic is not accidental, I am writing from the Sklifosovsky Hospital. Guess why?

What is an electric arc

This is one of the types of electric discharge in a gas (a physical phenomenon). It is also called - Arc discharge or Voltaic arc. Consists of ionized, electrically quasi-neutral gas (plasma).

It can occur between two electrodes when the voltage between them increases, or when they approach each other.

Briefly about properties: electric arc temperature, from 2500 to 7000 °C. Not a small temperature, however. The interaction of metals with plasma leads to heating, oxidation, melting, evaporation and other types of corrosion. Accompanied by light radiation, blast and shock wave, ultra-high temperature, fire, ozone and carbon dioxide release.

There is a lot of information on the Internet about what an electric arc is, what its properties are, if you are interested in more details, look. For example, in en.wikipedia.org.

Now about my accident. It's hard to believe, but 2 days ago I directly encountered this phenomenon, and unsuccessfully. It was like this: on November 21, at work, I was instructed to make the wiring of the lamps in the junction box, and then connect them to the network. There were no problems with the wiring, but when I got into the shield, some difficulties arose. It’s a pity that the androyd forgot his house, didn’t take a photo of the electrical panel, otherwise it would be more clear. Maybe I'll do more when I get to work. So, the shield was very old - 3 phases, zero bus (aka grounding), 6 automata and a packet switch (it seems everything is simple), the condition was initially not credible. I struggled with a zero tire for a long time, since all the bolts were rusty, after which I easily put the phase on the machine. Everything is fine, I checked the lamps, they work.

After that, he returned to the shield to carefully lay the wires and close it. I want to note that the electrical panel was at a height of ~ 2 meters, in a narrow passage, and to get to it, I used a stepladder (ladder). Laying the wires, I found sparks on the contacts of other machines, which caused the lamps to blink. Accordingly, I extended all the contacts and continued to inspect the remaining wires (to do it once and not return to this again). Having discovered that one contact on the bag has a high temperature, I decided to extend it too. I took a screwdriver, leaned it against the screw, turned it, bang! There was an explosion, a flash, I was thrown back, hitting the wall, I fell to the floor, nothing was visible (blinded), the shield did not stop exploding and buzzing. Why the protection did not work I do not know. Feeling the falling sparks on me, I realized that I had to get out. I got out by touch, crawling. Having got out of this narrow passage, he began to call his partner. Already at that moment I felt that with my right hand(I held a screwdriver to her) something was wrong, a terrible pain was felt.

Together with my partner, we decided that we needed to run to the first-aid post. What happened next, I think it’s not worth telling, they just stung and went to the hospital. I will never forget that terrible sound of a long short circuit - itching with buzzing.

Now I'm in the hospital, I have an abrasion on my knee, the doctors think that I was shocked, this is a way out, so they monitor my heart. I believe that the current did not beat me, but the burn on my arm was caused by an electric arc that arose during the short circuit.

What happened there, why the short circuit happened, I don’t know yet, I think, when the screw was turned, the contact itself moved and a phase-to-phase short circuit occurred, or there was a bare wire behind the packet switch and when the screw approached electric arc. I'll find out later if they figure it out.

Damn, I went for a dressing, they wrapped my hand so much that I write with one left now)))

I didn’t take a photo without bandages, it’s not a very pleasant sight. I do not want to scare beginner electricians ....

What are the electric arc protection measures that could protect me? After analyzing the Internet, I saw that the most popular means of protecting people in electrical installations from an electric arc is a heat-resistant suit. In North America, special Siemens circuit breakers are very popular, which protect both from an electric arc and from maximum current. In Russia, at the moment, such machines are used only at high-voltage substations. In my case, a dielectric glove would be enough for me, but think for yourself how to connect lamps in them? It is very uncomfortable. I also recommend using goggles to protect your eyes.

In electrical installations, the fight against an electric arc is carried out using vacuum and oil circuit breakers, as well as using electromagnetic coils together with arc chutes.

It's all? Not! The most reliable way to protect yourself from an electric arc, in my opinion, are stress relief work . I don’t know about you, but I won’t work under stress anymore ...

This is my article electric arc and arc protection ends. Is there anything to add? Leave a comment.