Lightning discharges - lightning - are considered as electrical discharges of a giant capacitor, one plate of which is a thundercloud charged from the lower side (most often, negative charges), and the other is the earth, on the surface of which positive charges are induced (lightning discharges also pass between oppositely charged parts of the clouds). These categories consist of two stages: initial (leader) and main. In the initial stage, lightning slowly develops from a thundercloud to the earth's surface in the form of a faintly luminous ionized channel, which is filled with negative charges flowing from the cloud (Fig. 4.9).

Rice. 4.9 Thundercloud

A typical oscillogram of a lightning current wave passing through a struck object (Fig. 4.10) shows that within a few microseconds the lightning current rises to the maximum (amplitude) value i. This section of the wave (see Fig. 4.10, points 1-2) is called the time of the wave front t. This is followed by a current decay. The time from the beginning (point 1) to the moment when the lightning current, falling, reaches a value equal to half of its amplitude (points 1-4), is called the half-decay period T1

Important characteristics of the lightning current are also the amplitude and rate of rise of the lightning current (wave steepness).

The amplitude and steepness of the lightning current depend on many factors (the charge of the cloud, the conductivity of the earth, the height of the affected object, etc.) and vary widely. In practice, the amplitude of the wave is determined by the probability curves of lightning currents (Fig. 4.11).

On these curves, the amplitude values ​​of lightning currents Im are plotted along the ordinate axis, and the values ​​of the probability of occurrence of these currents are plotted along the abscissa axis.

The probability is expressed as a percentage. The upper curve characterizes lightning currents with a probability of up to 2%, and the lower curves - up to 80%. From the curves in Fig. 4.11 it can be seen that lightning currents in flat areas (curve 1) are approximately twice as large as lightning currents in mountainous areas (curve 2), where the soil resistivity is quite high. Curve 2 also applies to lightning currents falling into line wires and into towering objects with an object-to-earth contact resistance of the order of hundreds of ohms.

Lightning currents up to 50 kA are most often observed. Lightning currents over 50 kA do not exceed 15% in flat areas and 2.5% in gambling areas. The average steepness of the lightning current is 5 kA/µs.

Regardless of geographic latitude, the polarity of the lightning discharge current can be both positive and negative, which is associated with the conditions for the formation and separation of charges in thunderclouds. However, in most cases, lightning currents have a negative polarity, i.e., a negative charge is transferred from the cloud to the ground, and only in rare cases are positive polarity currents recorded.

It is with lightning currents (negative and positive polarity) that the occurrence of overvoltages in electrical installations, including wired communication devices, is often associated. There are two types of lightning current impact: a direct lightning strike (p.o.m.) in the communication line and indirect effects of lightning currents during a lightning discharge near the LS. As a result of both influences in the wires of the communication line, overvoltages from p. m. and induced overvoltage, united under the general name atmospheric overvoltage.

With a direct lightning strike, overvoltages of up to several million volts appear, which can cause destruction or damage to the communication line equipment (poles, traverses, insulators, cable inserts), as well as wired communication equipment included in the line wires. Frequency p. at. m. is directly dependent on the intensity of thunderstorm activity in a given area, which is characterized by the total annual duration of thunderstorms, expressed in hours or thunderstorm days.

The intensity of lightning discharges is characterized by the magnitude of the lightning current. Observations carried out in many countries have established that the magnitude of the current in the channels of lightning discharges ranges from several hundred amperes to several hundred thousand amperes. The duration of lightning ranges from a few microseconds to a few milliseconds.

The discharge current has a pulsed character with a front part, called the wave front, and a back part, called the wave decay. The time of the wave front of the lightning current is denoted by x µs, the time of wave decay to 1/2 of the current amplitude is denoted by t.

The equivalent lightning frequency is the frequency of the sinusoidal current, which, acting in the cable sheath instead of a pulsed wave, causes a voltage between the core and the sheath with an amplitude equal to the amplitude for the natural lightning current. On average, m = 5 kHz.

The equivalent lightning current is the effective value of the sinusoidal current with the equivalent lightning frequency. The average value of the current during impacts to the ground is 30 kA.

The number and extent of damages that occur during the year on an underground communication cable depend on a number of reasons:

Intensity of lightning activity in the cable laying area;

Design, dimensions and material of external protective covers, electrical conductivity, mechanical strength of insulating coatings and belt insulation, as well as electrical strength of insulation between the cores;

Resistivity, chemical composition and physical structure of the soil, its humidity and temperature;

The geological structure of the terrain and the area of ​​the cable route;

The presence of high objects near the cable, such as masts, power transmission and communication poles, tall trees, forests, etc.

The degree of lightning resistance of a cable to lightning strikes is characterized by the quality factor of the cable q and is determined by the ratio of the maximum allowable shock voltage to the ohmic resistance of the metal cover of the cable over a length of 1 km:

Cable damage does not occur with every lightning strike. A dangerous lightning strike is such a strike in which the resulting voltage exceeds the breakdown voltage of the cable in amplitude at one or more points. With the same dangerous impact, several cable damages can occur.

When lightning strikes at some distance from the cable, an electric arc occurs towards the cable. The greater the amplitude of the current, the greater the distance from which an arc can occur. The width of the equivalent strip adjacent to the cable, impacts to which cause damage to the cable, is taken on average to be 30 m (with the cable in the middle). The area occupied by this strip forms the equivalent affected area, it is obtained by multiplying the width of the equivalent strip by the length of the cable.

The Main Directorate of the Ministry of Emergency Situations of Russia for Yakutia recalls that a thunderstorm is one of the most dangerous natural phenomena for humans. A lightning strike can cause paralysis, loss of consciousness, respiratory and cardiac arrest. In order not to suffer from a lightning strike, you need to know and follow some rules of behavior during a thunderstorm.

First of all, it must be remembered that lightning—it is an electric discharge of high voltage, huge current, high power and very high temperature that occurs in nature. Electrical discharges that occur between cumulus clouds or between a cloud and the ground are accompanied by thunder, heavy rain, often hail and squally winds.

Employees of the republican department of the Ministry of Emergency Situations give a number of simple tips on what to do during a thunderstorm.

When you are in a country or garden house during a thunderstorm, you should:

—Close doors and windows, exclude drafts.

—Do not heat the stove, close the chimney, because the smoke coming out of the chimney has a high electrical conductivity and can attract an electrical discharge.

—Turn off the TV, radio, electrical appliances, turn off the antenna.

— Turn off the means of communication: laptop, mobile phone.

—You should not be near a window or in the attic, as well as near massive metal objects.

—Do not be in an open area near metal structures, power lines.

—Do not touch anything wet, iron, electrical.

— Remove all metal jewelry from yourself (chains, rings, earrings), put them in a leather or plastic bag.

—Don't open your umbrella.

—Never seek shelter under large trees.

—It is undesirable to be near a fire.

—Stay away from wire fences.

—Don't go out to take off clothes that are drying on the clotheslines, as they also conduct electricity.

—Do not ride a bicycle or motorcycle.

— It is very dangerous to talk on a mobile phone during a thunderstorm, it must be turned off.

So that lightning does not strike if you are in a car

The machine protects the people inside quite well, because even with a lightning strike, the discharge goes through the surface of the metal. If you are in your car in a thunderstorm, close your windows, turn off your radio, cell phone, and GPS. Do not touch door handles or other metal parts.

To avoid being struck by lightning if you are on a motorcycle

A bicycle and a motorcycle, unlike a car, will not save you from a thunderstorm. It is necessary to dismount and move about 30 m away from the bicycle or motorcycle.

Help for the victim of a lightning strike

To provide first aid to a person struck by lightning, immediately move him to a safe place. Touching the victim is not dangerous, there is no charge left in his body. Even if it seems that defeat is fatal, it may turn out that in fact it is not.

If the victim is unconscious, lay him on his back and turn his head to the side so that the tongue does not sink into the airways. It is necessary to do artificial respiration and heart massage until the ambulance arrives.

If these actions helped, the person shows signs of life, before the arrival of doctors, give the victim two or three tablets of analgin and put a wet and folded tissue on his head. If there are burns, they must be poured with plenty of water, the burnt clothing should be removed, and then the affected area should be covered with a clean dressing. When transporting to a medical institution, it is necessary to put the victim on a stretcher and constantly monitor his well-being.

For relatively mild lightning injuries, give the victim any painkiller (analgin, tempalgin, etc.) and a sedative medicine (valerian tincture, corvalol, etc.)

The air shell around the globe consists of several layers: troposphere (upper boundary 7 - 18 km), stratosphere (height from 7 18 km above the earth - up to 80 km), ionosphere (from 80 to 900 km). The ionosphere is a well-conducting medium, which is, as it were, the lining of a huge spherical capacitor, the second lining of which is the spherical surface of the earth; the air medium between them can be considered as a dielectric. The upper lining (ionosphere) is positively charged, the earth's surface is negatively charged. The electric field strength of such a natural capacitor is uneven due to different air densities, at the earth's surface it is 120 V/m. The electric field strength in the atmosphere varies and depends on the presence of charged clouds.

The total electric field strength at the earth's surface can reach 5000 V/m and more. At critical potential differences between the cloud and the ground (over 10 9 V), an electric discharge occurs, i.e. lightning.

On fig. 1.5, a shows a direct lightning strike into the cable without breakdown of the core insulation.

Line 1 - cable sheath, 2 - two cable cores.

Rice. 1.5. Direct hit of lightning current into the cable

When lightning strikes the cable sheath, the current spreads to the left and right and induces an EMF in the cable (U ob-zh - between the sheath and the core, U well-zh - between the cores) and currents i f. These EMFs can be dangerous for the insulation of cable cores and equipment connected to them. If at the same time the insulation between the shell and the conductors breaks through, then the lightning current will also enter the conductors (Fig. 1.5, b), while at the place of the lightning strike, the voltages Uob-zh = 0, U well-zh = 0, in remote places these EMF can reach dangerous values.

On fig. 1.6 shows cases of indirect action of lightning discharges.

Rice. 1.6. Indirect action of a lightning discharge

When lightning strikes a tree, the discharge along its roots can pass into the cable (Fig. 1.6, a). Distance A, which is covered by the electric arc of lightning, increases with the increase in the resistivity of the earth.

The second case of indirect action is shown in Fig. 1.6, b: during a lightning discharge between clouds, the current induces in the cable (and overhead lines) EMF, which is proportional to the values.

1.6. High-frequency channels of transmission systems on high-voltage AC and DC power lines

The wires of high-voltage power lines, in addition to transmitting electrical energy, can be used to transmit communication signals, telecontrol and protection devices for power lines from emergency operation. These high-frequency channels are created at a frequency of 40-500 kHz.

The scheme for connecting high-frequency devices to power lines according to the "phase-to-ground" scheme is shown in fig. 1.7.

Each transmitter operates at its own frequency, its power is 10 100 W or more. The influence of high-frequency channels on the channels of transmission systems (air, cable communication lines, and others) should be considered if the power of high-frequency posts exceeds 5 W.

Powerful transmitting radio stations also belong to the sources of influence.

Rice. 1.7. Scheme for connecting high-frequency devices to power lines: I, II - high-frequency posts (communications, telecontrol, protection devices); P 1, P 2 - transceivers; Ф 1, Ф 2 - filters; C1, C2 - capacitors; L 1 , L 2 - blocking chokes that do not pass high-frequency signals to power equipment; f 1 , f 2 - carrier frequencies

Lightning strikes, lightning, are one of the highest energy phenomena on Earth, and, in fact, they are more than just a bright flash of light and a roar of thunder. Lightning discharges, as it has long been known, are the source of flashes of gamma rays, and recently a group of researchers from Japan found out that these gamma-ray flashes are, in turn, the initiator of photonuclear reactions in the atmosphere, as a result of which antimatter is produced, which immediately annihilates in contact with ordinary matter.

© Kyoto University/Teruaki Enoto

Gamma-ray flashes from lightning discharges were first recorded in 1992 by NASA's Compton Gamma-ray Observatory. Since then, these flashes, called Terrestrial Gamma-ray Flashes (TGFs), have been closely studied, and only recently, researchers from the University of Kyoto managed to find explanations for some of the features of the signals from these flashes.

“We have known for a long time that lightning discharges emit gamma rays. Based on this, a hypothesis was put forward that these gamma rays would provoke nuclear reactions in which the atoms of some elements of the earth's atmosphere take part. says Teruaki Enoto, lead researcher,“The west coast zone of Japan in winter is an ideal place to observe severe thunderstorms and lightning. In 2015, we began installing a network of miniature gamma sensors on the coast, and now the data collected by these sensors has allowed us to unravel some of the mysteries of lightning.

During a thunderstorm that raged on February 6 of this year, gamma sensors collected a very unusual set of data. Four sensors installed near the city of Kashiwazaki registered a strong gamma-ray burst immediately after a close lightning strike. But when scientists conducted a thorough analysis of the data, they found that in fact one burst consists of three consecutive bursts of different durations.

The first, shortest burst, lasting less than a millisecond, is the product of a lightning discharge. But the next two bursts are of greater interest to scientists, because they are the result of photonuclear reactions that occur when gamma rays from the first burst knock out neutrons from atmospheric nitrogen atoms. The knocked-out free neutrons are absorbed by other atoms, which leads to the appearance of a glow in the gamma range, which lasts for several tens of milliseconds.

The duration of the last, third gamma-ray burst, is already about one minute, and the reason for its appearance is even more exotic than the reason for the appearance of the second burst. Nitrogen atoms that have lost neutrons become unstable and decay, releasing positrons into space, which are a by-product of the fission reaction. Positrons are the opposite of electrons on the antimatter side, and when they collide with normal electrons, they annihilate, mutually destroying each other. And such a process of "suicide" of positrons-electrons is also accompanied by bursts of gamma rays.

In the near future, Japanese scientists plan to install a number of additional gamma sensors, which, together with the 10 already available, will allow them to collect more data and study the phenomena described above even more thoroughly.

“Many of the people believe that antimatter is something that exists only in science fiction” says Terueki Enoto,“But we argue that the process of the appearance and self-destruction of antimatter is the most common thing for the Earth. In some regions, such phenomena occur many times almost every day.”

Contributed by Kyoto University via Science Daily
The study was published in the journal

Lightning discharges (lightning) are the most common source of powerful electromagnetic interference of natural origin. According to approximate estimates, about a hundred lightning strikes the earth's surface every second. Surrounding objects, electrical structures, means of communication, RES, wildlife are adversely affected by lightning:

− electrostatic;

− electromagnetic;

− dynamic;

− thermal;

− biological.

Lightning strikes often lead to the death of people and cause great material damage.

Lightning is a kind of gas discharge with a very long spark. The total length of the lightning channel reaches several kilometers. The source of lightning is a thundercloud, which carries an accumulation of volumetric positive and negative charges. The formation of such space charges of different polarity in the cloud (cloud polarization) is associated with condensation due to the cooling of water vapor of ascending warm air flows on positive and negative moisture droplets in the cloud under the action of intense ascending air flows.

In nature, there are three main types of lightning discharges:

1. Linear lightning - has the form of a narrow strip between the cloud and the ground, between clouds or between individual accumulations of space charges within the cloud.

2. Ball lightning is a brightly luminous, mobile, convex, relatively stable plasma clot that appears and disappears for reasons that are currently little understood.

3. Silent discharges - a corona that occurs in places of sharp inhomogeneity of the electric field strength on protruding grounded objects in the pre-thunderstorm period and during a thunderstorm.

Linear lightning (hereinafter referred to as lightning) is the most common in nature and, in comparison with other types of lightning discharges, is the most common source of powerful electromagnetic interference.

Lightning discharge develops in different ways. Intra-cloud discharges most often occur during thunderstorms that occur high above the ground. Under such conditions, it is easier for lightning to develop from the bottom of a charged cloud to the top or vice versa than to go a long way from the base of the cloud, i.e. edge closest to the ground, to the ground. Intracloud discharges are often observed in arid regions, where clouds are higher above the earth's surface than in regions with a humid climate.

For middle latitudes, where clouds are located at a height of about 1–3 km, the number of intracloud discharges and discharges between clouds and the ground is almost the same.

The polarization of the cloud in the process of charge separation does not occur in the same way. In 75 ÷ 85% of all cases, the base of the cloud carries a negative charge, and during the discharge process, it is the charge of this polarity that is transferred to the earth. At the same time, the amplitude value of the lightning current with its negative polarity is on average 1.5 ÷ 2 times lower than with positive polarity.

The mechanism of formation of linear lightning is associated with the gradual accumulation of electric charges of different polarities on the upper and lower parts of the cloud and the formation of an electric field of increasing intensity around it. When the potential gradient at any point in the cloud reaches a critical value for air (at normal atmospheric pressure of about 3 10 6 V/m), lightning occurs at that point, which begins with a leader stage and ends with a reverse (main) discharge. The main stage of a lightning discharge is the source of PEMF. Due to the fact that several clusters of charges isolated from each other are formed in the cloud, lightning is usually multiple, i.e. consists of several single discharges developing along the same path. The average duration of the main discharge is 20 ÷ 50 µs; the number of repeated discharges can vary from 2 to 10 or more; time interval between repeated discharges 0.001 ÷ 0.5 s. As the measurements show, the lightning discharge current is a pulse with a rapid increase in current from zero to a maximum (wave front) and a relatively slow decline (wave tail).

When implementing protection measures and determining the electromagnetic environment (EMS) in a particular area, the following values ​​of the main values ​​of the lightning characteristic can be taken as calculated values.