January 17, 2012 at 10:00

When opening electrical circuit an electrical discharge occurs in the form of an electric arc. For an electric arc to occur, it is sufficient that the voltage at the contacts be above 10 V with a current in the circuit of the order of 0.1 A or more. At significant voltages and currents, the temperature inside the arc can reach 10...15 thousand °C, as a result of which contacts and current-carrying parts melt.

At voltages of 110 kV and higher, the arc length can reach several meters. Therefore, an electric arc, especially in powerful power circuits, at voltages above 1 kV is a great danger, although serious consequences can also occur in installations at voltages below 1 kV. As a result, the electric arc must be limited as much as possible and quickly extinguished in circuits with voltages both above and below 1 kV.

Causes of electric arcs

The process of electric arc formation can be simplified as follows. When the contacts diverge, the contact pressure and, accordingly, the contact surface initially decrease, the transition resistance (current density and temperature) increases - local (in certain areas of the contact area) overheating begins, which further contribute to thermionic emission when, under the influence of high temperature, the speed of electron movement increases and they break out from the surface of the electrode.

At the moment the contacts diverge, that is, the circuit breaks, the voltage is quickly restored at the contact gap. Since the distance between the contacts is small, a high-intensity electric field arises, under the influence of which electrons are ejected from the surface of the electrode. They accelerate into electric field and when they hit a neutral atom, they give it their kinetic energy. If this energy is enough to remove at least one electron from the shell of a neutral atom, then the process of ionization occurs.

The resulting free electrons and ions make up the plasma of the arc barrel, that is, the ionized channel in which the arc burns and continuous movement of particles is ensured. In this case, negatively charged particles, primarily electrons, move in one direction (towards the anode), and atoms and gas molecules lacking one or more electrons - positively charged particles - in the opposite direction (towards the cathode). The conductivity of plasma is close to the conductivity of metals.

A large current passes through the arc shaft and creates high temperature. This temperature of the arc barrel leads to thermal ionization - the process of formation of ions due to the collision of molecules and atoms with high kinetic energy at high speeds of their movement (molecules and atoms of the medium where the arc burns disintegrate into electrons and positively charged ions). Intense thermal ionization maintains high plasma conductivity. Therefore, the voltage drop along the arc length is small.

In an electric arc, two processes continuously occur: in addition to ionization, also deionization of atoms and molecules. The latter occurs mainly through diffusion, that is, the transfer of charged particles into environment, and the recombination of electrons and positively charged ions, which recombine into neutral particles, releasing the energy expended in their decay. In this case, heat is dissipated into the environment.

Thus, it is possible to distinguish three stages of the process under consideration: arc ignition, when, due to impact ionization and electron emission from the cathode, an arc discharge begins and the ionization intensity is higher than deionization; stable arc combustion, supported by thermal ionization in the arc barrel, when the intensity of ionization and deionization is the same, arc extinction when the intensity of deionization is higher than ionization.

Methods for extinguishing arcs in electrical switching devices

In order to disconnect the elements of the electrical circuit and avoid damage to the switching device, it is necessary not only to open its contacts, but also to extinguish the arc that appears between them. The processes of arc extinguishing, as well as combustion, under alternating and DC are different. This is determined by the fact that in the first case, the current in the arc passes through zero every half-cycle. At these moments, the release of energy in the arc stops and the arc spontaneously goes out each time, and then lights up again.

In practice, the current in the arc becomes close to zero somewhat earlier than the transition through zero, since as the current decreases, the energy supplied to the arc decreases, and the arc temperature decreases accordingly and thermal ionization stops. In this case, the deionization process occurs intensively in the arc gap. If in at the moment open and quickly separate the contacts, then subsequent electrical breakdown may not occur and the circuit will be disconnected without arcing. However, in practice this is extremely difficult to do, and therefore they accept special measures accelerated arc extinction, providing cooling of the arc space and reducing the number of charged particles.

As a result of deionization, the electrical strength of the gap gradually increases and at the same time the recovery voltage across it increases. The ratio of these quantities determines whether the arc will light up for the next half of the period or not. If the electrical strength of the gap increases faster and there is more restoring voltage, the arc will no longer ignite, otherwise a stable arc will be ensured. The first condition determines the task of extinguishing the arc.

In switching devices they use various ways arc extinction.

Arc lengthening

When the contacts diverge during the process of disconnecting the electrical circuit, the resulting arc stretches. At the same time, the cooling conditions for the arc improve, since its surface increases and more voltage is required for combustion.

Dividing a long arc into a number of short arcs

If the arc formed when the contacts open is divided into K short arcs, for example by drawing it into a metal grid, then it will go out. The arc is usually drawn into the metal grid by the force electro magnetic field induced in the grid plates by eddy currents. This arc extinguishing method is widely used in switching devices for voltages below 1 kV, in particular in automatic air circuit breakers.

Arc cooling in narrow slots

Extinguishing the arc in a small volume is easier. Therefore, in switching devices, arc-extinguishing chambers with longitudinal slots are widely used (the axis of such a slot coincides in the direction with the axis of the arc shaft). Such a gap usually forms in chambers made of insulating arc-resistant materials. Due to the contact of the arc with cold surfaces, intense cooling occurs, diffusion of charged particles into the environment and, accordingly, rapid deionization.

In addition to slots with plane-parallel walls, slots with ribs, protrusions, and extensions (pockets) are also used. All this leads to deformation of the arc barrel and helps to increase the area of ​​contact with the cold walls of the chamber.

The drawing of an arc into narrow slots usually occurs under the influence of a magnetic field interacting with the arc, which can be considered as a conductor with current.

The external magnetic field to move the arc is most often provided by a coil connected in series with the contacts between which the arc occurs. Arc extinction in narrow slots is used in devices for all voltages.

High pressure arc extinguishing

At a constant temperature, the degree of gas ionization decreases with increasing pressure, while the thermal conductivity of the gas increases. All other things being equal, this leads to increased cooling of the arc. Extinguishing the arc using high pressure, created by the arc itself in tightly closed chambers, is widely used in fuses and a number of other devices.

Arc extinction in oil

If the switch contacts are placed in oil, the arc that occurs when they open leads to intense evaporation of the oil. As a result, a gas bubble (sheath) is formed around the arc, consisting mainly of hydrogen (70...80%), as well as oil vapor. The released gases penetrate directly into the arc shaft area at high speed, cause mixing of cold and hot gas in the bubble, provide intense cooling and, accordingly, deionization of the arc gap. In addition, the deionizing ability of gases increases the pressure inside the bubble created during the rapid decomposition of oil.

The intensity of the arc extinguishing process in oil is higher, the closer the arc comes into contact with the oil and the faster the oil moves relative to the arc. Taking this into account, the arc rupture is limited by a closed insulating device - an arc extinguishing chamber. In these chambers, closer contact of the oil with the arc is created, and with the help of insulating plates and exhaust holes, working channels are formed through which the oil and gases move, providing intense blowing of the arc.

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 connected by welding.

The welding arc, depending on the environment in which it occurs, is divided into several groups. It can be open, closed, or in a protective gas environment.

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

An electric arc differs in the type of current supplied - alternating or direct - and in the duration of combustion - pulsed or stationary. In addition, the arc can have direct or reverse polarity.

Based on the type of electrode used, non-melting and melting are distinguished. The use of a particular electrode directly depends on the characteristics that it has 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 fused to the original workpiece.

The arc gap can be conditionally divided into three characteristic sections: near-cathode, near-anode, and also the arc shaft. In this case, the last section, i.e. The arc shaft 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 areas.

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. Consists of the sum on each of the areas: barrel, near-cathode and near-anode. In this case, the change in voltage in the near-electrode regions is significantly greater than in the remaining region.

3. Temperature. An electric arc, depending on the composition of the gaseous medium and the material of the electrodes, can develop a temperature of up to 12 thousand degrees Kelvin. However, such peaks are not located over the entire plane of the electrode end. Because even with the most better processing the material of the conductive part has various irregularities and tubercles, due to which many discharges occur, which are perceived as one. Of course, the arc temperature 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 increase.

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

Introduction

Methods for extinguishing an electric arc... The topic is relevant and interesting. So let's begin. We ask ourselves the questions: What is an electric arc? How to control it? What processes occur during its formation? What does it consist of? And what it looks like.

What is an electric arc?

Electric arc (Voltaic arc, Arc discharge) is a physical phenomenon, one of the types of electrical discharge in a gas. It was first described in 1802 by the Russian scientist V.V. Petrov.

Electric arc is a special case of the fourth form of state of matter - plasma - and consists of an ionized, electrically quasi-neutral gas. The presence of free electric charges ensures the conductivity of the electric arc.

Arc formation and properties

When the voltage between two electrodes increases to a certain level, an electrical breakdown occurs in the air between the electrodes. The electrical breakdown voltage depends on the distance between the electrodes, etc. Often, to initiate breakdown at the existing voltage, the electrodes are brought closer to each other. During a breakdown, a spark discharge usually occurs between the electrodes, pulse-closing the electrical circuit.

Electrons in spark discharges ionize molecules in the air gap between the electrodes. With sufficient power of the voltage source, a sufficient amount of plasma is formed in the air gap so that the breakdown voltage (or air gap resistance) in this place drops significantly. In this case, spark discharges turn into an arc discharge - a plasma cord between the electrodes, which is a plasma tunnel. This arc is essentially a conductor, and closes the electrical circuit between the electrodes, the average current increases even more, heating the arc to 5000-50000 K. In this case, it is considered that the ignition of the arc is completed.

The interaction of electrodes with arc plasma leads to their heating, partial melting, evaporation, oxidation and other types of corrosion. An electric welding arc is a powerful electrical discharge flowing in a gaseous environment. An arc discharge is characterized by two main features: the release of a significant amount of heat and a strong light effect. The temperature of a conventional welding arc is about 6000°C.

Arc light is dazzlingly bright and is used in a variety of lighting applications. The arc radiates large number visible and invisible thermal (infrared) and chemical (ultraviolet) rays. Invisible rays cause inflammation of the eyes and burn human skin, so welders use special shields and special clothing to protect against them.

Using an arc

Depending on the environment in which the arc discharge occurs, the following welding arcs are distinguished:

1. Open arc. Burns in the air. The composition of the gas environment of the arc zone is air mixed with vapors of the metal being welded, the material of the electrodes and electrode coatings.

2. Closed arc. Burns under a layer of flux. The composition of the gas environment of the arc zone - vapor of the base metal, electrode material and protective flux.

3. Arc with supply of protective gases. Various gases are fed into the arc under pressure - helium, argon, carbon dioxide, hydrogen, illuminating gas and various mixtures of gases. The composition of the gas environment in the arc zone is an atmosphere of protective gas, vapor of the electrode material and the base metal.

The arc can be powered from direct or alternating current sources. In the case of DC power, a distinction is made between an arc of direct polarity (minus the power source on the electrode, plus on the base metal) and reverse polarity (minus on the base metal, plus on the electrode). Depending on the material of the electrodes, arcs are distinguished with fusible (metal) and non-fusible (carbon, tungsten, ceramic, etc.) electrodes.

When welding, the arc can be of direct action (the base metal participates in the electrical circuit of the arc) and indirect action (the base metal does not participate in the electrical circuit of the arc). The arc of indirect action is used relatively little.

The current density in the welding arc can be different. Arcs are used with a normal current density - 10--20 a/mm2 (regular manual welding, welding in some shielding gases) and with a high current density - 80--120 a/mm2 and more (automatic, semi-automatic submerged arc welding, in a protective gas environment).

The occurrence of an arc discharge is possible only in the case when the gas column between the electrode and the base metal is ionized, that is, it contains ions and electrons. This is achieved by imparting the appropriate energy to the gas molecule or atom, called ionization energy, as a result of which electrons are released from the atoms and molecules. The arc discharge medium can be represented as a gas conductor electric current having a round-cylindrical shape. The arc consists of three regions - the cathode region, the arc column, and the anode region.

During arc burning, active spots are observed on the electrode and base metal, which are heated areas on the surface of the electrode and base metal; The entire arc current passes through these spots. On the cathode, the spot is called cathode, on the anode - anodic. The cross section of the middle part of the arc column is several more sizes cathode and anode spots. Its size accordingly depends on the size of active spots.

The arc voltage varies depending on the current density. This dependence, depicted graphically, is called the static characteristic of the arc. At low values ​​of current density, the static characteristic has a decreasing character, i.e., the arc voltage decreases as the current increases. This is due to the fact that with increasing current, the cross-sectional area of ​​the arc column and electrical conductivity increase, and the current density and potential gradient in the arc column decrease. The magnitude of the cathode and anode arc voltage drops does not change with the current value and depends only on the electrode material, base metal, gas environment and gas pressure in the arc zone.

At current densities of the welding arc of conventional modes used for manual welding, the arc voltage does not depend on the current value, since the cross-sectional area of ​​the arc column increases in proportion to the current, and the electrical conductivity changes very little, and the current density in the arc column practically remains constant. In this case, the magnitude of the cathode and anode voltage drops remains unchanged. In an arc of high current density, with increasing current strength, the cathode spot and the cross-section of the arc column cannot increase, although the current density increases in proportion to the current strength. In this case, the temperature and electrical conductivity of the arc column increase slightly.

Voltage electric field and the potential gradient of the arc column will increase with increasing current. The cathode voltage drop increases, as a result of which the static characteristic will have an increasing character, i.e., the arc voltage will increase with increasing arc current. Increasing static characteristic is a feature of high current density arcs in various gas environments. Static characteristics refer to the steady stationary state of the arc with its length unchanged.

A stable arc burning process during welding can occur if certain conditions are met. The stability of the arc burning process is influenced by a number of factors; voltage idle speed arc power source, type of current, current magnitude, polarity, presence of inductance in the arc circuit, presence of capacitance, current frequency, etc.

Contribute to improving arc stability by increasing the current, open-circuit voltage of the arc power source, including inductance in the arc circuit, increasing the frequency of the current (when powered by alternating current) and a number of other conditions. Stability can also be significantly improved through the use of special electrode coatings, fluxes, shielding gases and a number of other technological factors.

extinguishing electric arc welding

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

What is an electric arc

This is one of the types of electrical discharge in gas (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 approaches each other.

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

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, take a look. For example, in ru.wikipedia.org.

Now about my accident. It's hard to believe, but 2 days ago I directly encountered this phenomenon, and unsuccessfully. It happened like this: on November 21, at work, I was tasked with wiring lamps in a junction box and then connecting them to the network. There were no problems with the wiring, but when I climbed into the shield, some difficulties arose. It’s a pity I forgot my android at home, I didn’t take a photo of the electrical panel, otherwise it would have been more clear. Maybe I'll do more when I get back to work. So, the shield was very old - 3 phases, a zero bus (also known as grounding), 6 circuit breakers and a package switch (it seemed simple), the condition initially did not inspire confidence. I struggled with the zero bus for a long time, since all the bolts were rusty, after which I easily installed the phase on the machine. Everything is fine, I checked the lamps, they work.

Afterwards, I returned to the switchboard to carefully lay the wires and close it. I would like to note that the electrical panel was located at a height of ~2 meters, in a narrow passage, and to get to it, I used a stepladder (ladder). While laying out the wires, I discovered sparks on the contacts of other machines, which caused the lamps to blink. Accordingly, I pulled out all the contacts and continued inspecting 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. I don't know why the protection didn't work. 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 the screwdriver to her) something was wrong, I felt terrible pain.

Together with my partner, we decided that we needed to run to the first aid station. I don’t think it’s worth telling what happened next, I just got injected and went to the hospital. I will never forget this terrible sound of a long short circuit - itching with a buzzing sound.

Now I’m in the hospital, I have an abrasion on my knee, the doctors think that I was electrocuted, this is the way out, so they are monitoring my heart. I believe that I was not shocked, but the burn on my hand was caused by an electric arc that occurred during a short circuit.

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

Damn, I went to get a bandage, they wrapped my hand so much that I’m writing with my left hand now)))

I didn’t take a photo without bandages; it was a very unpleasant sight. I don’t want to scare novice 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 electric arcs is a heat-resistant suit. IN North America Special machines from Siemens are very popular, they protect against both electric arc and 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 about how to connect lamps in them? This is very inconvenient. I also recommend using safety glasses to protect your eyes.

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

This is all? No! The most reliable way to protect yourself from an electric arc, in my opinion, is stress relief work . I don’t know about you, but I won’t work under voltage anymore...

That's it for my article electric arc And arc protection ends. Do you have anything to add? Leave a comment.

Electric welding arc- this is a long-term electrical discharge in plasma, which is a mixture of ionized gases and vapors of components protective atmosphere, filler and base metal.

The arc gets its name from the characteristic shape it takes when burning between two horizontally located electrodes; heated gases tend to rise upward and this electrical discharge bends, taking the shape of an arch or arc.

From a practical point of view, the arc can be considered as a gas conductor that transforms electrical energy to thermal. It provides high heating intensity and is easily controlled through electrical parameters.

A common characteristic of gases is that under normal conditions they are not conductors of electric current. However, when favorable conditions(high temperature and the presence of an external high-intensity electric field) gases can be ionized, i.e. their atoms or molecules can release or, for electronegative elements, on the contrary, capture electrons, turning into positive or negative ions, respectively. Thanks to these changes, gases move into the fourth state of matter called plasma, which is electrically conductive.

Excitation of the welding arc occurs in several stages. For example, when welding MIG/MAG, when the end of the electrode and the part being welded come into contact, contact occurs between the micro protrusions of their surfaces. The high current density contributes to the rapid melting of these protrusions and the formation of a layer of liquid metal, which constantly increases towards the electrode, and eventually ruptures.

At the moment of rupture of the jumper, rapid evaporation of the metal occurs, and the discharge gap is filled with ions and electrons arising in this case. Due to the fact that voltage is applied to the electrode and the product, electrons and ions begin to move: electrons and negatively charged ions to the anode, and positively charged ions to the cathode, and thus a welding arc is excited. After the arc is excited, the concentration of free electrons and positive ions in the arc gap continues to increase, since electrons collide with atoms and molecules on their way and “knock out” even more electrons from them (at the same time, atoms that have lost one or more electrons become positively charged ions ). Intense ionization of the gas in the arc gap occurs and the arc acquires the character of a stable arc discharge.

A few fractions of a second after the arc is excited, a weld pool begins to form on the base metal, and a drop of metal begins to form at the end of the electrode. And after about another 50 - 100 milliseconds, a stable transfer of metal from the end of the electrode wire into the weld pool is established. It can be carried out either by drops that freely fly over the arc gap, or by drops that first form a short circuit and then flow into the weld pool.

The electrical properties of the arc are determined by the processes occurring in its three characteristic zones - the column, as well as in the near-electrode regions of the arc (cathode and anode), which are located between the arc column on the one hand and the electrode and the product on the other.

To maintain the arc plasma when welding with a consumable electrode, it is enough to provide a current of 10 to 1000 amperes and apply an electric voltage of about 15 to 40 volts between the electrode and the product. In this case, the voltage drop across the arc column itself will not exceed several volts. The remaining voltage drops at the cathode and anode regions of the arc. The length of the arc column on average reaches 10 mm, which corresponds to approximately 99% of the arc length. Thus, the electric field strength in the arc column lies in the range from 0.1 to 1.0 V/mm. The cathode and anode regions, on the contrary, are characterized by a very short length (about 0.0001 mm for the cathode region, which corresponds to the mean free path of the ion, and 0.001 mm for the anodic region, which corresponds to the mean free path of the electron). Accordingly, these regions have a very high electric field strength (up to 104 V/mm for the cathode region and up to 103 V/mm for the anodic region).

It has been experimentally established that for the case of welding with a consumable electrode, the voltage drop in the cathode region exceeds the voltage drop in the anode region: 12 - 20 V and 2 - 8 V, respectively. Considering that the release of heat on electrical circuit objects depends on current and voltage, it becomes clear that when welding with a consumable electrode, more heat is released in the area where more voltage drops, i.e. in the cathode. Therefore, when welding with a consumable electrode, mainly the reverse polarity of the welding current is used, when the product serves as the cathode to ensure deep penetration of the base metal (in this case, the positive pole of the power source is connected to the electrode). Direct polarity is sometimes used when performing surfacing (when the penetration of the base metal, on the contrary, is desirable to be minimal).

Under TIG welding conditions (non-consumable electrode welding), the cathode voltage drop, on the contrary, is significantly lower than the anode voltage drop and, accordingly, under these conditions more heat is generated at the anode. Therefore, when welding with a non-consumable electrode, to ensure deep penetration of the base metal, the product is connected to the positive terminal of the power source (and it becomes the anode), and the electrode is connected to the negative terminal (thus, also protecting the electrode from overheating).

In this case, regardless of the type of electrode (consumable or non-consumable), heat is generated mainly in the active regions of the arc (cathode and anode), and not in the arc column. This property of the arc is used to melt only those areas of the base metal to which the arc is directed.

Those parts of the electrodes through which the arc current passes are called active spots (on the positive electrode - anode spot, and on the negative electrode - cathode spot). The cathode spot is a source of free electrons, which contribute to the ionization of the arc gap. At the same time, streams of positive ions rush towards the cathode, bombarding it and transferring their kinetic energy to it. The temperature on the cathode surface in the area of ​​the active spot during welding with a consumable electrode reaches 2500 ... 3000 °C.

Lk - cathode region; La - anode region (La = Lk = 10 -5 -10 -3 cm); Lst - arc column; Ld - arc length; Ld = Lk + La + Lst

Streams of electrons and negatively charged ions rush to the anode spot, which transfer their kinetic energy to it. The temperature on the anode surface in the area of ​​the active spot during welding with a consumable electrode reaches 2500 ... 4000°C. The temperature of the arc column when welding with a consumable electrode ranges from 7,000 to 18,000 ° C (for comparison: the melting point of steel is approximately 1500 ° C).

Influence on the arc of magnetic fields

When welding with direct current, a phenomenon such as magnetic is often observed. It is characterized by the following features:

The welding arc column sharply deviates from its normal position;
- the arc burns unsteadily and often breaks off;
- the sound of the arc burning changes - popping sounds appear.

Magnetic blast disrupts the formation of the seam and can contribute to the appearance of such defects in the seam as lack of penetration and lack of fusion. The cause of magnetic blast is the interaction of the magnetic field of the welding arc with other nearby magnetic fields or ferromagnetic masses.

The welding arc column can be considered as part of the welding circuit in the form of a flexible conductor around which there is a magnetic field.

As a result of the interaction of the magnetic field of the arc and the magnetic field that arises in the part being welded during the passage of current, the welding arc is deflected in the direction opposite to the place where the current conductor is connected.

The influence of ferromagnetic masses on arc deflection is due to the fact that, due to the large difference in resistance to the passage of magnetic field lines of the arc through air and through ferromagnetic materials (iron and its alloys), the magnetic field turns out to be more concentrated on the side opposite to the location of the mass, so the arc column shifts to the side ferromagnetic body.

The magnetic field of the welding arc increases with increasing welding current. Therefore, the effect of magnetic blast is more often manifested when welding at high conditions.

You can reduce the influence of magnetic blast on the welding process:

Performing short arc welding;
- tilting the electrode so that its end is directed towards the action of the magnetic blast;
- bringing the current supply closer to the arc.

The effect of magnetic blast can also be reduced by replacing direct welding current with alternating current, in which the magnetic blast appears much less. However, it must be remembered that the alternating current arc is less stable, since due to the change in polarity it goes out and lights up again 100 times per second. In order for the alternating current arc to burn stably, it is necessary to use arc stabilizers (easily ionized elements), which are introduced, for example, into the electrode coating or into the flux.