When lightning protection is needed. Lightning protection of buildings and structures without explosive zones

A lightning strike directly into a building causes a fire due to deformation of materials, sudden and strong increase their temperatures. Therefore, lightning protection of buildings and structures is necessary element in the equipment of any civil, administrative or industrial facility. This is a set of technical measures to ensure the safety of the structure, equipment, property and people in the building. And this is far from a far-fetched problem, since on average more than 40 thousand thunderstorms occur on the planet per day. But there is another aspect to modern world is damage or complete failure of electronic equipment as a result of overload caused by even remote lightning discharges. And this is a very significant problem in the times of computers and the Internet.

To prevent this from happening, a comprehensive system of lightning protection for buildings and structures has been developed. A lightning strike, even at a distance of several hundred meters from an object, causes a powerful impulse that can travel to nearby buildings, damage it and create a fire. Due to the different nature of the threats, two systems have been developed: external lightning protection of buildings and structures and internal. Each of them is designed to solve specific problems.

External system must catch lightning heading into a building, transport it through a special outlet into the ground, while completely blocking the possibility of causing damage to the structure and the people in it. Internal lightning protection can reduce electromagnetic effects on communication systems located at the facility. Such systems are mandatory introduced by regulatory documents both at the stages of project development, construction or reconstruction, and for the operational period of all types of facilities and industrial communications, regardless of ownership and But the situation is far from being so simple, since there are two documents: lightning protection of buildings and structures SO 153-34.21.122-2003 and RD 34.21.122-87. These instructions are not equivalent.

Fundamentally, the lightning protection device for buildings and structures depends on the functions that it must perform. The external system consists of an lightning rod, a down conductor and a grounding element. The internal one is more complex - these are lightning arresters, protection devices against sparks and gas, barriers for lightning protection. In America and Europe, the requirements for these systems are much higher than in our country. Lightning protection devices there activate their functions already in the event of a threat of discharge due to special sensors capable of detecting an increase in voltage in the atmosphere. These are so-called rod lightning rods. They are able to protect much large area.

People have long understood that high-quality lightning protection of buildings and structures means ensuring the safety of people and property from the threat of fire and death. This is primarily a guarantee of your own well-being.

The need for lightning protection of ground-based objects is prescribed primarily by classifying buildings and structures as lightning protection in accordance with RD 34.21.122-87 “Instructions for lightning protection of buildings and structures.” The instruction establishes the necessary set of measures and measures designed to ensure the safety of people (farm animals), to protect buildings, structures, equipment and materials from explosions, fires and destruction possible due to lightning. The requirements of the instructions are observed when developing projects for the construction of buildings and structures.

Today, the problem is often considered to be the owner’s desire to build a facility at the lowest cost, which pushes them to carry out construction without proper design study, with the involvement of unskilled third-party labor, as well as to use materials and equipment from “random” manufacturers.

Despite the differentiated approach to solving issues of providing lightning protection to buildings and structures, there are a number of conventions, uncertainties and ambiguous interpretations of a number of conditions in Table 1 current instructions on the design of lightning protection creates erroneous opinions in design decisions, which leads to either underestimation or overestimation of the requirements for lightning protection equipment of buildings and structures. Today, the ambiguity of interpretations of RD also complicates the correctness and necessity of designing lightning protection. Ambiguous interpretation of lightning protection of architectural monuments by the number of thunderstorm hours, uncertainty in clause 9 of Table 1 on lightning protection of small buildings, lack of practical instructions for lightning protection of metal building elements (roof elements, etc.), use of grounding and, finally, lack of practice in applying IEC requirements – all this leads to a situation where the problem of lightning protection of ground-based objects is becoming global. Together with the lack of proper supervision, everything leads to the fact that often constructed objects suffer considerable losses, primarily of an economic nature. And the confidence that such a small structure is struck by lightning 1-2 times a century frees in most cases the need for lightning protection for residential buildings in rural areas, gardens and country houses.

Back in the 50s of the last century, regulatory documents regulating the requirements for lightning protection of buildings and structures prescribed methods for lightning protection of houses in rural areas. A number of examples of reliable protection against direct lightning strikes were given. The types of lightning rods were indicated depending on the configuration and geometric dimensions. The types of materials from which lightning rods were made were given. Despite the requirements for the use of factory-made lightning protection elements, it was allowed to use lightning rods from improvised means to protect private households. Black iron with a minimum diameter of 6 mm was used as lightning protection elements. Down conductors and grounding conductors were also made of similar material and were laid over combustible building structures or placed in the ground, regardless of the properties of the soil. In a number of cases, such methods of protection against manifestations of atmospheric electricity contributed to the independent equipping of buildings and structures of the agricultural complex, as well as residential buildings, mainly in rural areas, with lightning protection. This policy in the field of protection against atmospheric electricity was also partly due to the lack of required quantity organizations with sufficient practical experience in the field of lightning protection, publications on the study of lightning phenomena, installation of lightning protection, etc. In addition, first of all, the regulatory documents paid attention to the high-quality and mandatory implementation of lightning protection of government facilities.

MINISTRY OF ENERGY AND ELECTRIFICATION OF THE USSR

Developer State Research Energy Institute named after. G.M. Krzhizhanovsky

Instructions for the installation of lightning protection of buildings and structures. RD 34.21.122-87

The instruction establishes a set of measures and devices to ensure the safety of people (farm animals), to protect buildings, structures, equipment and materials from explosions, fires, and destruction due to lightning. The instruction is mandatory for all ministries and departments.

Intended for specialists designing buildings and structures.

PREFACE

The requirements of this Instruction are mandatory for all ministries and departments.

The instruction establishes the necessary set of measures and devices designed to ensure the safety of people (farm animals), protect buildings, structures, equipment and materials from explosions, fires and destruction possible due to lightning.

The instructions must be followed when developing projects for buildings and structures.

The instructions do not apply to the design and installation of lightning protection of power lines, electrical parts of power plants and substations, contact networks, radio and television antennas, telegraph, telephone and radio broadcast lines, as well as buildings and structures whose operation is associated with the use, production or storage of gunpowder and explosives.

This Instruction regulates lightning protection measures carried out during construction and does not exclude the use of additional lightning protection means inside a building or structure during reconstruction or installation of additional technological or electrical equipment.

When developing designs for buildings and structures, in addition to the requirements of the Instructions, the requirements for lightning protection of other applicable standards, rules, instructions, state standards.

With the entry into force of this Instruction, the “Instructions for the design and installation of lightning protection of buildings and structures” SN 305-77 becomes invalid.

1. GENERAL PROVISIONS

1.1. In accordance with the purpose of buildings and structures, the need for lightning protection and its category, and when using rod and cable lightning rods, the type of protection zone are determined according to table. 1 depending on the average annual duration of thunderstorms at the location of the building or structure, as well as on the expected number of lightning strikes per year. A lightning protection device is mandatory if the conditions written in columns 3 and 4 of the table are simultaneously met. 1.

An assessment of the average annual duration of thunderstorms and the expected number of lightning damage to buildings or structures is carried out in accordance with Appendix 2; construction of protection zones of various types - according to Appendix 3.

Table 1

Item no.	Buildings and constructions	Location	Type of protection zone when using rod and cable lightning rods	Lightning protection category
1	2	3	4	5
1	Buildings and structures or parts thereof, the premises of which, according to the PUE, belong to zones of classes B-I and B-II	Throughout the USSR	Zone A	I
2	The same classes B-Ia, B-Ib, B-IIa		With the expected number of lightning strikes per year of a building or structure N>1 - zone A; at N≤1 - zone B	II
3	Outdoor installations that create, according to the PUE, a class B-Ig zone	Throughout the USSR	Zone B	II
4	Buildings and structures or parts thereof, the premises of which, according to the PUE, belong to the zones classes P-I, P-II, P-IIa		For buildings and structures of I and II degrees of fire resistance at 0.1 2-zone A	III
5	Small buildings located in rural areas of III - V degrees of fire resistance, the premises of which, according to the PUE, belong to zones of classes P-I, P-II, P-IIa	In areas with an average duration of thunderstorms of 20 hours per year or more at N	-	III (clause 2.30)
6	Outdoor installations and open warehouses, creating, according to the PUE, a zone of classes P-III	In areas with an average duration of thunderstorms of 20 hours per year or more	At 0.1 2 - zone A	III
7	Buildings and structures of III, IIIa, IIIb, IV, V degrees of fire resistance, in which there are no premises classified according to the PUE as explosion and fire hazardous class zones	Same	At 0.1 2 - zone A	III
8	Buildings and structures made of light metal structures with combustible insulation (IVa degree of fire resistance), in which there are no premises classified according to the PUE as explosion and fire hazardous class zones	In areas with an average duration of thunderstorms of 10 hours per year or more	At 0.1 2 - zone A	III
9	Small buildings of III-V degrees of fire resistance, located in rural areas, in which there are no premises classified according to the PUE as zones of explosion and fire hazardous classes	In areas with an average duration of thunderstorms of 20 hours per year or more for III, IIIa, IIIb, IV, V degrees of fire resistance at N	-	III (clause 2.30)
10	Computer center buildings, including those located in urban areas	In areas with an average duration of thunderstorms of 20 hours per year or more	Zone B	II
11	Livestock and poultry buildings and structures of III-V degrees of fire resistance: for large cattle and pigs for 100 heads or more, for sheep for 500 heads or more, for poultry for 1000 heads or more, for horses for 40 heads or more	In areas with an average duration of thunderstorms of 40 hours per year or more	Zone B	III
12	Smoke and other pipes of enterprises and boiler houses, towers and derricks for all purposes with a height of 15 m or more	In areas with an average duration of thunderstorms of 10 hours per year or more	-	III (clause 2.31)
13	Residential and public buildings, the height of which is more than 25 m higher than the average height of surrounding buildings within a radius of 400 m, as well as free-standing buildings with a height of more than 30 m, distant from other buildings by more than 400 m	In areas with an average duration of thunderstorms of 20 hours per year or more	Zone B.	III
14	Detached residential and public buildings in rural areas with a height of more than 30 m	Same	Zone B	III
15	Public buildings of III-V degrees of fire resistance for the following purposes: children's preschool institutions, schools and boarding schools, hospitals of medical institutions, dormitories and canteens of healthcare and recreation institutions, cultural, educational and entertainment institutions, administrative buildings, train stations, hotels, motels and campsites	Same	Zone B	III
16	Open entertainment institutions (auditoriums of open cinemas, stands of open stadiums, etc.)	Same	Zone B	III
17	Buildings and structures that are monuments of history, architecture and culture (sculptures, obelisks, etc.)	Same	Zone B	III

1.2. Buildings and structures classified as lightning protection categories I and II must be protected from direct lightning strikes, its secondary manifestations and the introduction of high potential through ground (aboveground) and underground metal communications.

Buildings and structures classified as category III according to lightning protection must be protected from direct lightning strikes and the introduction of high potential through ground (overground) metal communications. Outdoor installations classified as Category II according to lightning protection must be protected from direct strikes and secondary manifestations of lightning.

Outdoor installations classified as category III according to lightning protection must be protected from direct lightning strikes.

Inside large buildings (more than 100 m wide), it is necessary to carry out potential equalization measures.

1.3. For buildings and structures with premises requiring lightning protection devices of categories I and II or categories I and III, lightning protection of the entire building or structure should be carried out according to category I.

If the area of ​​premises of lightning protection category I is less than 30% of the area of ​​all premises of the building (on all floors), lightning protection of the entire building is allowed to be carried out according to category II, regardless of the category of the remaining premises. At the same time, at the entrance to premises of category I, protection must be provided against the introduction of high potential through underground and ground (overground) communications, carried out in accordance with paragraphs. 2.8 and 2.9.

1.4. For buildings and structures with premises requiring lightning protection devices of categories II and III, lightning protection of the entire building or structure should be carried out according to category II

If the area of ​​premises of lightning protection category II is less than 30% of the area of ​​all premises of the building (on all floors), lightning protection of the entire building is allowed to be carried out according to category III. At the same time, at the entrance to premises of category II, protection must be provided against the introduction of high potential through underground and ground (overground) communications, carried out in accordance with paragraphs. 2.22 and 2.23.

1.5. For buildings and structures, at least 30% total area which fall on premises requiring lightning protection devices of category I, II or III, lightning protection of this part of buildings and structures must be carried out in accordance with clause 1.2.

For buildings and structures, more than 70% of the total area of ​​which are premises that are not subject to lightning protection according to Table. 1, and the rest of the building consists of premises of I, II or III categories of lightning protection, only protection against the introduction of high potentials through communications introduced into premises subject to lightning protection should be provided: for category I - in accordance with paragraphs. 2.8, 2.9; for categories II and III - by connecting communications to the grounding device of electrical installations, corresponding to the instructions in clause 1.7, or to the reinforced concrete foundation reinforcement of the building (taking into account the requirements of clause 1.8). The same connection must be provided for internal communications(not input from outside)

1.6. In order to protect buildings and structures of any category from direct lightning strikes, existing high structures should be used as natural lightning rods as much as possible ( chimneys, water towers, floodlight masts, overhead power lines, etc.), as well as lightning rods of other nearby structures.

If a building or structure partially fits into the protection zone of natural lightning rods or neighboring objects, protection from direct lightning strikes should be provided only for the remaining, unprotected part. If, during the operation of a building or structure, reconstruction or dismantling of neighboring facilities will lead to an increase in this unprotected part, corresponding changes in protection against direct lightning strikes must be made before the start of the next thunderstorm season; if dismantling or reconstruction of neighboring facilities is carried out during the thunderstorm season, during this time temporary measures must be provided to provide protection from direct lightning strikes to the unprotected part of the building or structure.

1.7. All grounding conductors recommended by the PUE for electrical installations may be used as lightning protection grounding conductors, with the exception of the neutral wires of overhead power lines with voltages up to 1 kV.

1.8. Reinforced concrete foundations of buildings, structures, external installations, lightning rod supports should, as a rule, be used as lightning protection grounding conductors, provided that continuous electrical communication on their reinforcement and connecting it to embedded parts by welding.

Bitumen and bitumen-latex coatings are not an obstacle to such use of foundations. In moderately and highly aggressive soils, where protection of reinforced concrete from corrosion is carried out with Epoxy and other polymer coatings, and also when soil moisture is less than 3%, the use of reinforced concrete foundations as grounding conductors is not allowed.

Artificial grounding conductors should be located under asphalt pavement or in rarely visited places (on lawns, at a distance of 5 m or more from dirt roads and pedestrian roads, etc.).

1.9. Potential equalization inside buildings and structures with a width of more than 100 m should occur due to a continuous electrical connection between load-bearing intra-shop structures and reinforced concrete foundations, if the latter can be used as grounding conductors in accordance with clause 1.8.

Otherwise, installation inside the building in the ground must be ensured at a depth of at least 0.5 m extended horizontal electrodes with a cross-section of at least 100 mm. Electrodes should be laid at least every 60 m along the width of the building and connect it along its ends on both sides to the external ground loop.

1.10. In frequently visited open areas with an increased risk of lightning strikes (near monuments, television towers and similar structures over 100 meters high). m) potential equalization is carried out by connecting down conductors or reinforcement of the structure to its reinforced concrete foundation at least after 25 m along the perimeter of the base of the structure.

If it is impossible to use reinforced concrete foundations as grounding conductors under the asphalt surface of the site at a depth of at least 0.5 m every 25 m radially diverging horizontal electrodes with a cross section of at least 100 must be laid mm and length 2-3 m, connected to the grounding conductors to protect the structure from direct lightning strikes.

1.11. When erected during a thunderstorm tall buildings and structures on them during construction, starting from a height of 20 m, it is necessary to provide the following temporary lightning protection measures. At the top level of the facility under construction, lightning rods must be fixed, which through metal structures or down conductors freely descending along the walls should be connected to the grounding conductors specified in paragraphs. 3.7 and 3.8. The protection zone of type B lightning rods must include all outdoor areas where people may be present during construction. Connections of lightning protection elements can be welded or bolted. As the height of the facility under construction increases, lightning rods should be moved higher.

When erecting high metal structures, their bases at the beginning of construction must be connected to the grounding conductors specified in paragraphs. 3.7 and 3.8.

1.12. Lightning protection devices and measures that meet the requirements of these standards must be included in the design and schedule of construction or reconstruction of a building or structure in such a way that lightning protection occurs simultaneously with the main construction and installation work.

1.13. Lightning protection devices for buildings and structures must be accepted and put into operation by the start of finishing work, and in the presence of explosive zones - before the start of comprehensive testing of process equipment.

At the same time, design documentation for the lightning protection device (drawings and explanatory note) and acceptance certificates for lightning protection devices, including acts for hidden work on connecting grounding conductors to down conductors and down conductors to lightning rods, are drawn up and transferred to the customer, with the exception of cases of using steel building frame as down conductors and lightning rods, as well as the results of measurements of the resistance to industrial frequency current of grounding conductors of free-standing lightning rods.

1.14. The condition of lightning protection devices must be checked for buildings and structures of categories I and II once a year before the start of the thunderstorm season, for buildings and structures of category III - at least once every 3 years.

Integrity and protection against corrosion must be checked available for review parts of lightning rods and down conductors and contacts between them, as well as the value of the resistance to industrial frequency current of grounding conductors of free-standing lightning rods. This value should not exceed the results of corresponding measurements at the acceptance stage by more than 5 times (clause 1.13). Otherwise, the ground electrode should be inspected.

2. REQUIREMENTS FOR LIGHTNING PROTECTION OF BUILDINGS AND STRUCTURES. LIGHTNING PROTECTION CATEGORY I

2.1. Protection against direct lightning strikes of buildings and structures classified as Category I according to lightning protection design must be carried out with free-standing rod (Fig. 1) or cable (Fig. 2) lightning rods.

Rice. 1. Free-standing lightning rod:
1 - protected object; 2 - metal communications

Rice. 2. Free-standing cable lightning rod. The designations are the same as in Fig. 1

The specified lightning rods must provide a protection zone of type A in accordance with the requirements of Appendix 3. At the same time, the removal of lightning rod elements from the protected object and underground metal communications is ensured in accordance with paragraphs. 2.3, 2.4, 2.5.

2.2. The choice of ground electrode for protection against direct lightning strikes (natural or artificial) is determined by the requirements of clause 1.8.

At the same time, the following designs of grounding conductors are acceptable for free-standing lightning rods (Table 2):

a) one (or more) reinforced concrete footrest with a length of at least 2 m or one (or more) reinforced concrete pile with a length of at least 5 m;

b) one (or more) buried in the ground at least 5 m reinforced concrete support post with a diameter of at least 0.25 m;

c) reinforced concrete foundation of arbitrary shape with a surface area of ​​contact with the ground of at least 10 m 2;

d) an artificial grounding system consisting of three or more vertical electrodes with a length of at least 3 m, united by a horizontal electrode, with a distance between the vertical electrodes of at least 5 m. The minimum cross-sections (diameters) of electrodes are determined according to table. 3.

table 2

Ground electrode	Sketch	Dimensions m
Reinforced concrete footrest		a ≥ 1.8 b ≥ 0.4 l ≥ 2.2
Reinforced concrete pile		d = 0.25-0.4 l ≥ 5
Steel double rod: 40×4 strip mm rods with diameter d=10-20 mm		t ≥ 0.5 l = 3-5 c = 3-5
Steel three-bar: 40×4 strip mm rods with diameter d=10-20 mm		t ≥ 0.5 l = 3-5 c = 5-6

Table 3

Shape of down conductor and grounding conductor	Cross-section (diameter) of the down conductor and grounding conductor laid
	outside the building in the air	in the ground
Round down conductors and jumpers with a diameter of mm	6	-
Round vertical electrodes with a diameter of mm	-	10
Round horizontal* electrodes with a diameter of mm	-	10
Rectangular electrodes:
section, mm	48	160
thick, mm	4	4
* Only for equalizing potentials inside buildings and for laying external contours at the bottom of the pit around the perimeter of the building.

2.3. The smallest permissible distance S in the air from the protected object to the support (down conductor) of a rod or cable lightning rod (see Fig. 1 and 2) is determined depending on the height of the building, the design of the ground electrode and the equivalent electrical resistivity of the soil ρ, Ohm m.

For buildings and structures with a height of no more than 30 m the smallest permissible distance S in, m, equals:

at ρ Ohm m. for a ground electrode of any design given in clause 2.2, S in = 3 m;

at 100 Ohm m.

for ground electrodes consisting of one reinforced concrete pile, one reinforced concrete footing or a recessed post of a reinforced concrete support, the length of which is indicated in clause 2.2a, b, S c = 3+ l0 -2 (ρ—100);

for ground electrodes consisting of four reinforced concrete piles or footrests located in the corners of a rectangle at a distance of 3-8 m one from the other, or a reinforced concrete foundation of any shape with a surface area of ​​contact with the ground of at least 70 m 2 or artificial grounding conductors specified in clause 2.2d, S in = 4 m.

For buildings and structures of greater height, the value S in defined above must be increased by 1 m per every 10 m object height over 30 m.

2.4. The smallest permissible distance S in from the protected object to the cable in the middle of the span (Fig. 2) is determined depending on the design of the ground electrode, the equivalent soil resistivity ρ, Ohm m., and the total length l of lightning rods and down conductors.

At length l m the smallest permissible distance S in1, m, equals:

at ρ Ohm m. for a ground electrode of any design given in clause 2.2, S in1 = 3.5 m;

at 100 Ohm m.

for ground electrodes consisting of one reinforced concrete pile, one reinforced concrete footing or a buried post of a reinforced concrete support, the length of which is specified in clause 2.2a, b, S c = 3.5+3·10 -3 (ρ-100);

for ground electrodes consisting of four reinforced concrete piles or footings located at a distance of 3-8 m one from the other, or artificial grounding conductors specified in clause 2.2d, S in1 = 4 m.

At total length lightning rods and down conductors l = 200-300 m the smallest permissible distance S in1 must be increased by 2 m compared to the values ​​defined above.

2.5. To prevent the introduction of high potential into the protected building or structure through underground metal communications (including through electrical cables for any purpose), grounding conductors for protection against direct lightning strikes should be, if possible, removed from these communications at the maximum distances allowed by technological requirements. The smallest permissible distances S z, (see Fig. 1 and 2) in the ground between ground electrodes for protection against direct lightning strikes and communications introduced into buildings and structures of category 1 should be S z = S in + 2 ( m), with S in according to clause 2.3.

2.6. If there are direct gas outlet and breathing pipes on buildings and structures for the free removal of gases, vapors and suspensions of explosive concentrations into the atmosphere, the protection zone of lightning rods should include the space above the edge of the pipes, limited by a hemisphere with a radius of 5 m.

For gas outlet and breathing pipes equipped with caps or "goosenecks", the lightning rod protection zone should include the space above the edge of the pipes, limited by a cylinder of height H and radius R:

for gases heavier than air with excess pressure inside the installation less than 5.05 kPa (0,05 at) Н = 1 м, R = 2 m; 5,05-25,25 kPa (0,05 — 0,25 at) H = 2.5 m, R = 5 m,

for gases lighter than air at excess pressure inside the installation:

up to 25.25 kPa H=2.5 m, R = 5 m;

over 25.25 kPa H=5 m, R = 5 m

It is not necessary to include the space above the edge of pipes in the lightning rod protection zone: when gases of non-explosive concentration are released; presence of nitrogen respiration; with constantly burning torches and torches ignited at the moment of gas release; for exhaust ventilation shafts, safety and emergency valves, the release of gases of explosive concentrations from which is carried out only in emergency cases.

2.7. To protect against secondary manifestations of lightning, the following measures must be taken:

a) metal structures and housings of all equipment and apparatus located in the protected building must be connected to the grounding device of electrical installations specified in clause 1.7, or to the reinforced concrete foundation of the building (taking into account the requirements of clause 1.8). The minimum permissible distances in the ground between this grounding conductor and the grounding conductors for protection against direct lightning strikes must be in accordance with clause 2.5;

b) inside buildings and structures between pipelines and other extended metal structures in places of their mutual approach at a distance of less than 10 cm every 20 m jumpers should be welded or soldered from steel wire with a diameter of at least 5 mm or steel tape with a cross-section of at least 24 mm 2, for cables with metal sheaths or armor, jumpers must be made of flexible copper conductor in accordance with the instructions of SNiP 3.05.06-85;

c) in connections of pipeline elements or other extended metal objects, transition resistances of no more than 0.03 must be provided Ohm for each contact. If it is impossible to ensure contact with the specified transition resistance using bolted connections, it is necessary to install steel jumpers, the dimensions of which are indicated in subparagraph “b”.

2.8. Protection against the introduction of high potential through underground metal communications (pipelines, cables in outer metal sheaths or pipes) should be carried out by connecting them at the entrance to the building or structure to the reinforcement of its reinforced concrete foundation, and if it is impossible to use the latter as a grounding conductor, to an artificial grounding conductor, specified in clause 2.2.

2.9. Protection against the introduction of high potential through external ground (aboveground) metal communications must be carried out by grounding them at the entrance to the building or structure and at the two communications supports closest to this entry. Reinforced concrete foundations of the building or structure and each of the supports should be used as grounding conductors, and if such use is not possible (see clause 1.8), artificial grounding conductors should be used, in accordance with clause 2.2d.

2.10. Entering the building of overhead power lines with voltage up to 1 kV, telephone, radio, alarm networks should be carried out only with cables of at least 50 m with metal armor or sheath or cables laid in metal pipes.

At the entrance to the building, metal pipes, armor and cable sheaths, including those with an insulating coating of the metal shell (for example, ААШв, ААШп), must be connected to the reinforced concrete foundation of the building or (see clause 1.8) to an artificial ground electrode specified in paragraph .2.2g.

At the point where the overhead power line transitions into the cable, the metal armor and sheath of the cable, as well as the pins or hooks of the overhead line insulators must be connected to the ground electrode specified in clause 2.2d. The pins or hooks of insulators on the support of the overhead power line closest to the point of transition into the cable must be connected to the same grounding conductor.

In addition, at the point of transition of the overhead power line into the cable, closed air spark gaps of 2-3 lengths must be provided between each core of the cable and grounded elements. mm valve arrester installed low voltage, for example RVN-0.5.

Protection against the introduction of high potentials along overhead power lines with voltages above 1 kV, introduced into substations located in the protected building (in-shop or attached), must be carried out in accordance with the PUE.

LIGHTNING PROTECTION II CATEGORY

2.11. Protection against direct lightning strikes of buildings and structures of category II with a non-metallic roof must be carried out by free-standing or installed on the protected object by rod or cable lightning rods, providing a protection zone in accordance with the requirements of Table. 1, clause 2.6 and appendix 3. When installing lightning rods at a facility, at least two down conductors must be provided from each rod lightning rod or each rack of a cable lightning rod. If the roof slope is no more than 1:8, a lightning protection mesh can also be used, subject to the mandatory compliance with the requirements of clause 2.6.

The lightning protection mesh must be made of steel wire with a diameter of at least 6 mm and laid on the roof on top or under fireproof or fire-resistant insulation or waterproofing. The grid cell pitch should be no more than 6×6 m. The mesh nodes must be connected by welding. Metal elements protruding above the roof (pipes, shafts, ventilation devices) must be connected to the lightning rod mesh, and protruding non-metallic elements must be equipped with additional lightning rods, also connected to the lightning rod mesh.

The installation of lightning rods or the application of lightning protection mesh is not required for buildings and structures with metal trusses, provided that their roofs use fireproof or fire-resistant insulation and waterproofing.

On buildings and structures with a metal roof, the roof itself should be used as a lightning rod. In this case, all protruding non-metallic elements must be equipped with lightning rods connected to the metal of the roof, c. the requirements of clause 2.6 are also met.

Down conductors from a metal roof or lightning protection mesh must be laid to grounding conductors at least every 25 m along the perimeter of the building.

2.12. When laying lightning protection mesh and installing lightning rods on the protected object, wherever possible, metal structures of buildings and structures (columns, trusses, frames, fire escapes, etc., as well as reinforcement of reinforced concrete structures) should be used as down conductors, provided that continuous electrical connection in connections of structures and fittings with lightning rods and grounding conductors, usually performed by welding.

Down conductors laid on the outer walls of buildings should be located no closer than 3 m from entrances or in places inaccessible to human touch.

2.13. In all possible cases (see clause 1.8), reinforced concrete foundations of buildings and structures should be used as grounding conductors for protection against direct lightning strikes.

If it is impossible to use foundations, artificial grounding systems are provided:

in the presence of rod and cable lightning rods, each down conductor is connected to a grounding conductor that meets the requirements of clause 2.2d;

If there is a lightning protection mesh or a metal roof, an external contour of the following structure is laid along the perimeter of the building or structure:

in soils with equivalent resistivityρ ≤ 500 Ohm m with a building area of ​​more than 250 m 2 a circuit is made of horizontal electrodes laid in the ground at a depth of at least 0.5 m, and with a building area of ​​less than 250 m 2 one vertical or horizontal beam electrode 2-3 long is welded to this circuit at the points where the down conductors are connected m;

in soils with a resistivity of 500 Ohm m with a building area of ​​more than 900 m 2 it is enough to make a circuit only from horizontal electrodes, and if the building area is less than 900 m 2 At least two vertical or horizontal beam electrodes with a length of 2-3 are welded to this circuit at the points where the down conductors are connected m at a distance of 3-5 m one from the other.

In large buildings, an external ground loop can also be used to equalize the potential inside the building in accordance with the requirements of clause 1.9.

In all possible cases, the ground electrode for protection against direct lightning strikes must be combined with the ground electrode for electrical installations in accordance with the instructions in clause 1.7

2.14. When installing free-standing lightning rods, the distance from them in the air and in the ground to the protected object and the underground utilities introduced into it is not standardized.

2.15. Outdoor installations containing flammable and liquefied gases and flammable liquids should be protected from direct lightning strikes as follows:

a) installation casings made of reinforced concrete, metal casings of installations and individual tanks with a roof metal thickness of less than 4 mm must be equipped with lightning rods installed on the protected object or separately standing;

b) metal casings of installations and individual tanks with a roof metal thickness of 4 mm or more, as well as individual tanks with a capacity of less than 200 m 3 Regardless of the thickness of the roof metal, as well as the metal casings of thermally insulated installations, it is enough to connect to the ground electrode.

2.16. For tank farms containing liquefied gases with a total capacity of more than 8000 m 3, as well as for tank farms with buildings made of metal and reinforced concrete containing flammable gases and flammable liquids, with a total capacity of a group of tanks of more than 100 thousand. m 3 Protection against direct lightning strikes should, as a rule, be carried out with separate lightning rods.

2.17. Treatment facilities are subject to protection from direct lightning strikes if the flash point of the product contained in the wastewater exceeds its operating temperature by less than 10 °C. The lightning rod protection zone should include a space whose base extends beyond the treatment facility by 5 m on each side of its walls, and the height is equal to the height of the structure plus 3 m.

2.18. If there are gas outlet or breathing pipes in outdoor installations or in tanks (above or underground) containing flammable gases or flammable liquids, then they and the space above them (see clause 2.6) must be protected from direct lightning strikes. The same space is protected above the cut of the neck of the tanks into which the product is openly poured on the unloading rack. Breathing valves and the space above them, limited by a cylinder 2.5 in height, are also subject to protection from direct lightning strikes. m with radius 5 m.

For tanks with floating roofs or pontoons and the protection zone of lightning rods should include a space limited by a surface, any point of which is 5 m from flammable liquid in the annular gap.

2.19. For outdoor installations listed in paragraphs. 2.15 - 2.18, in the weaving of grounding conductors for protection against direct lightning strikes, whenever possible, one should use reinforced concrete foundations of these installations or (supports of free-standing lightning rods, or make artificial grounding conductors consisting of one vertical or horizontal electrode with a length of at least 5 m.

To these grounding conductors, placed at least every 50 m along the perimeter of the installation base, the housings of external installations or down conductors of lightning rods installed on them must be connected, the number of connections is at least two.

2.20. To protect buildings and structures from secondary manifestations of lightning, the following measures must be taken:

a) metal casings of all equipment and devices installed in the protected building (structure) must be connected to the grounding device of electrical installations that complies with the instructions of clause 1.7, or to the reinforced concrete foundation of the building (taking into account the requirements of clause 1.8);

b) inside the building between pipelines and other extended metal structures in places where they come together at a distance of less than 10 cm every 30 m jumpers must be made in accordance with the instructions in clause 2.76;

c) in flanged connections of pipelines inside the building, normal tightening of at least four bolts per flange should be ensured.

2.21. To protect outdoor installations from secondary manifestations of lightning, the metal casings of the devices installed on them must be connected to the grounding device of electrical equipment or to the grounding electrode for protection against direct lightning strikes.

On tanks with floating roofs or pontoons, it is necessary to install at least two flexible steel jumpers between the floating roofs or pontoons and the metal body of the tank or down conductors of lightning rods installed on the tank.

2.22. Protection against the introduction of high potential through underground communications is carried out by connecting them at the entrance to the building or structure to the grounding conductor of electrical installations or protection from direct lightning strikes.

2.23. Protection against the introduction of high potential through external ground (overground) communications is carried out by connecting them at the entrance to the building or structure to the ground electrode of electrical installations or protection from direct lightning strikes, and at the communication support closest to the entrance - to its reinforced concrete foundation. If it is impossible to use a foundation (see clause 1.8), an artificial grounding system must be installed, consisting of an isode vertical or horizontal electrode with a length of at least 5 m.

2.24. Protection against the introduction of high potential through overhead power lines, telephone, radio and alarm networks must be carried out in accordance with clause 2.10.

LIGHTNING PROTECTION CATEGORY III

2.25. Protection against direct lightning strikes of buildings and structures classified as category III according to the lightning protection device must be carried out using one of the methods specified in clause 2.11, in compliance with the requirements of clause. 2.12 and 2.14.

Moreover, in the case of using an air-termination mesh, the pitch of its cells should be no more than 12 × 12 m.

2.26. In all possible cases (see clause 1.7), reinforced concrete foundations of buildings and structures should be used as grounding conductors for protection against direct lightning strikes

If it is impossible to use them, artificial grounding conductors are used:

each down conductor from rod and cable lightning rods must be connected to a grounding conductor consisting of at least two vertical electrodes with a length of at least 3 m, united by a horizontal electrode with a length of at least 5 m;

when using a mesh or metal roof as lightning rods along the perimeter of a building in the ground at a depth of at least 0.5 m an external circuit consisting of horizontal electrodes must be laid. In soils with an equivalent resistivity of 500 Ohm m and a building area of ​​less than 900 m 2 One vertical or horizontal beam electrode with a length of 2-3 should be welded to this circuit at the places where the down conductors are connected. m.

The minimum permissible cross-sections (diameters) of artificial grounding electrodes are determined according to table. 3.

In large buildings (more than 100 m) an external grounding loop can also be used to equalize potentials inside the building in accordance with the requirements of clause 1.9

In all possible cases, the ground electrode for protection against direct lightning strikes must be combined with the ground electrode of the electrical installation specified in Chapter. 1.7 PUE.

2.27. When protecting buildings for cattle and stables with free-standing lightning rods, their supports and grounding conductors should be located no closer than 5 m from the entrance to the buildings.

When installing lightning rods or laying mesh on a protected structure, a reinforced concrete foundation should be used as grounding conductors (see clause 1.8) or an external contour laid along the perimeter of the building under asphalt or concrete blind area in accordance with the instructions of clause 2.26.

Metal structures, equipment and pipelines located inside the building, as well as electrical potential equalization devices must be connected to the grounding conductors for protection against direct lightning strikes.

2.28. Protection from direct lightning strikes of metal sculptures and obelisks specified in clause 17 of table. 1 is ensured by connecting them to a ground electrode of any design given in clause 2.26.

If there are frequently visited sites near such high-height structures, potential equalization must be carried out in accordance with clause 1.10.

2.29. Lightning protection of outdoor installations containing flammable liquids with a vapor flash point above 61 °C and corresponding to clause 6 of table. 1 must be done as follows:

a) installation housings made of reinforced concrete, as well as metal housings of installations and tanks with a roof thickness of less than 4 mm must be equipped with lightning rods installed on the protected structure or free-standing;

b) metal housings of installations and tanks with a roof thickness of 4 mm and more should be connected to the ground electrode. The designs of grounding conductors must meet the requirements of clause 2.19.

2.30. Small buildings located in rural areas with non-metal roofing, corresponding to those specified in paragraphs. 5 and 9 tables. 1, are subject to protection from direct lightning strikes by one of the simplified methods:

a) if there are trees at a distance of 3-10 m from the building that are 2 times or more greater than its height, taking into account all objects protruding on the roof (chimneys, antennas, etc.), a down conductor must be laid along the trunk of the nearest tree , the upper end of which protrudes above the tree crown by at least 0.2 m. At the base of the tree, the down conductor must be connected to the ground electrode;

b) if the ridge of the roof corresponds to the highest height of the building, a cable lightning rod must be suspended above it, rising above the ridge by at least 0.25 m. Wooden planks fixed to the walls of the building can serve as supports for the lightning rod. Down conductors are laid on both sides along the end walls of the building and connected to grounding conductors. With a building length of less than 10 m grounding conductors can be made only on one side;

c) if there is a chimney rising above all elements of the roof, an air-termination rod with a height of at least 0.2 should be installed above it m, lay a down conductor along the roof and wall of the building and connect it to the ground electrode;

d) if there is a metal roof, it should be connected to the ground electrode at least at one point; in this case, external down conductors can serve metal stairs, gutters, etc. All metal objects protruding from it must be attached to the roof.

In all cases, lightning rods and down conductors with a minimum diameter of 6 should be used mm, and as a grounding electrode - one vertical or horizontal electrode 2-3 m minimum diameter 10 mm, laid at a depth of at least 0.5 m.

Connections of lightning rod elements are allowed to be welded or bolted.

2.31. Protection against direct lightning strikes of non-metallic pipes, towers, towers with a height of more than 15 m should be done by installing on these structures at their height:

up to 5 Ohm— one rod lightning rod with a height of at least 1 m;

from 50 to 150 m— two rod lightning rods with a height of at least 1 m, connected at the upper end of the pipe;

more than 150 m- at least three rod lightning rods with a height of 0.2 - 0.5 m or a steel ring with a cross-section of at least 160 must be laid along the upper end of the pipe mm 2 .

A protective cap installed on a chimney or metal structures such as antennas installed on television towers can also be used as a lightning rod.

With a building height of up to 50 m one down conductor must be laid from lightning rods; with a building height of more than 50 m down conductors must be laid at least every 25 m along the perimeter of the base of the structure, there are a minimum of two.

The cross-sections (diameters) of down conductors must meet the requirements of Table. 3, and in areas with high gas pollution or aggressive emissions into the atmosphere, the diameters of down conductors must be at least 12 mm.

Walking metal ladders, including those with bolted links, and other vertical metal structures can be used as down conductors.

On reinforced concrete pipes, reinforcing bars should be used as down conductors, connected along the height of the pipe by welding, twisting or overlapping; In this case, the laying of external down conductors is not required. The connection of the lightning rod to the fittings must be made at least at two points.

All connections of lightning rods to down conductors must be made by welding.

For metal pipes, towers, towers, the installation of lightning rods and the laying of down conductors is not required.

As grounding conductors for protecting metal and non-metallic pipes, towers, and derricks from direct lightning strikes, their reinforced concrete foundations should be used in accordance with clause 1.8. If it is impossible to use foundations, an artificial grounding conductor consisting of two rods connected by a horizontal electrode must be provided for each down conductor (see Table 2); with the perimeter of the base of the structure no more than 25 m an artificial ground electrode can be made in the form of a horizontal circuit laid at a depth of at least 0.5 m and made of a round cross-section electrode (see Table 3). When using reinforcing bars as down conductors in a structure, their connections with artificial grounding conductors must be made at least every 25 m with a minimum number of connections equal to two.

When constructing non-metallic pipes, towers, derricks, metal structures of installation equipment (freight-and-passenger and mine hoists, jib cranes, etc.) must be connected to grounding conductors. In this case, temporary lightning protection measures may not be carried out during the construction period. 22

2.32. To protect against the introduction of high potential through external ground (aboveground) metal communications, they must be connected to the ground electrode of electrical installations or protection from direct lightning strikes at the entrance to the building or structure.

2.33. Protection against high potential drift through overhead power lines with voltage up to 1 kV and communication and signaling lines must be carried out in accordance with the PUE and departmental regulatory documents.

3. LIGHTNING DRIVE DESIGNS

3.1. The supports of rod lightning rods must be designed for mechanical strength as free-standing structures, and the supports of cable lightning rods - taking into account the tension of the cable and the effect of wind and ice loads on it.

3.2. The supports of free-standing lightning rods can be made of any grade of steel, reinforced concrete or wood.

3.3. Rod lightning rods must be made of steel of any grade with a cross-section of at least 100 mm 2 and a length of at least 200 mm and are protected from corrosion by galvanizing, tinning or painting.

Cable lightning rods must be made of multi-wire steel ropes with a cross-section of at least 35 mm 2 .

3.4. Connections of lightning rods to down conductors and down conductors to grounding conductors should, as a rule, be made by welding, and if hot work is prohibited, bolted connections with a transition resistance of no more than 0.05 are allowed Ohm with mandatory annual monitoring of the latter before the start of the thunderstorm season.

3.5. Down conductors connecting lightning rods of all types with grounding conductors should be made of steel with dimensions no less than those indicated in the table. 3.

3.6. When installing lightning rods on a protected object and it is impossible to use metal structures of the building as down conductors (see clause 2.12), the down conductors must be laid to grounding conductors along the outer walls of the building along the shortest routes.

3.7. It is allowed to use any structures of reinforced concrete foundations of buildings and structures (pile, strip, etc.) as natural lightning protection grounding conductors (taking into account the requirements of clause 1.8).

The permissible dimensions of single structures of reinforced concrete foundations used as grounding conductors are given in Table. 2.

ANNEX 1

BASIC TERMS

1. Direct lightning strike (lightning strike) - direct contact of the lightning channel with a building or structure, accompanied by the flow of lightning current through it.

2. The secondary manifestation of lightning is the induction of potentials on metal structural elements, equipment, in open metal circuits, caused by nearby lightning discharges and creating the danger of sparking inside the protected object.

3. The introduction of high potential is the transfer into the protected building or structure through long metal communications (underground, above-ground and above-ground pipelines, cables, etc.) of electrical potentials that arise during direct and close lightning strikes and create the danger of sparking inside the protected object.

4. Lightning rod - a device that receives a lightning strike and diverts its current into the ground.

In general, a lightning rod consists of a support; lightning rod that directly perceives a lightning strike; a down conductor through which lightning current is transmitted to the ground; a grounding conductor that ensures the lightning current spreads in the ground.

In some cases, the functions of a support, lightning rod and down conductor are combined, for example, when using metal pipes or trusses as a lightning rod.

5. Lightning rod protection zone - the space inside which a building or structure is protected from direct lightning strikes with a reliability not lower than a certain value. The surface of the protection zone has the least and constant reliability; in the depths of the protection zone, reliability is higher than on its surface.

Type A protection zone has a reliability of 99.5% or higher, and type B has a reliability of 95% or higher.

6. Structurally, lightning rods are divided into the following types:

rod - with a vertical lightning rod;

cable (extended) - with a horizontal lightning rod mounted on two grounded supports;

meshes are multiple horizontal lightning rods intersecting at right angles and placed on the protected object.

7. Free-standing lightning rods are those whose supports are installed on the ground at some distance from the protected object.

8. A single lightning rod is a single design of a rod or cable lightning rod.

9. Double (multiple) lightning rod is two (or more) rod or cable lightning rods forming a common protection zone.

10. Lightning protection grounding conductor - one or more conductors buried in the ground, designed to drain lightning currents into the ground or limit overvoltages that occur on metal buildings, equipment, and communications during close lightning strikes. Grounding electrodes are divided into natural and artificial.

11. Natural grounding conductors - metal and reinforced concrete structures of buildings and structures buried in the ground.

12. Artificial grounding conductors - contours made of strip or round steel specially laid in the ground; concentrated structures consisting of vertical and horizontal conductors.

APPENDIX 2

CHARACTERISTICS OF THE INTENSITY OF LIGHTNING ACTIVITY AND LIGHTNING POSSIBILITY OF BUILDINGS AND STRUCTURES

The average annual duration of thunderstorms in hours at an arbitrary point on the territory of the USSR is determined from a map (Fig. 3), or from regional maps of the duration of thunderstorms approved for some regions of the USSR, or from average long-term (about 10 years) data from the weather station closest to the location of the building or structures.

The expected number N of lightning strikes per year is calculated using the formulas:

for concentrated buildings and structures (chimneys, derricks, towers)

N = 9π h 2 n 10 -6;

N = [ (S + 6h) (L + 6h) - 7.7h 2 ] n 10 -6,

where h is the greatest height of the building or structure, m; S, L - respectively the width and length of the building or structure, m; n - average annual number of lightning strikes in 1 km the earth's surface (specific density, lightning strikes into the ground) at the location of the building or structure.

For buildings and structures of complex configuration, the width and length of the smallest rectangle into which the building or structure can be inscribed in the plan are considered as S and L.

For an arbitrary point on the territory of the USSR, the specific density of lightning strikes into the ground n is determined based on the average annual duration of thunderstorms in hours as follows:

Rice. 3. Map of the annual average duration of thunderstorms in hours for the territory of the USSR

APPENDIX 3

LIGHTNING DRIVE PROTECTION ZONES

1. Single rod lightning rod.

The protection zone of a single rod lightning rod with a height h is a circular cone (Fig. A3.1), the top of which is at a height h 0

1.1. Protection zones of single rod lightning rods with height h ≤ 150 m have the following overall dimensions.

Zone A:	h 0 = 0.85 h,
	r 0 = (1.1 - 0.002 h) h,
	r x = (1.1 - 0.002 h) (h - h x / 0.85).
Zone B:	h0 = 0.92h
	r 0 = 1.5 h;
	r x =1.5 (h - h x / 0.92)

For zone B, the height of a single lightning rod at known values h and can be determined by the formula

h = (r x + 1.63 h x) / 1.5.

Rice. P3.1. Protection zone of a single rod lightning rod:
I - the border of the protection zone at level hx, 2 - the same at ground level

1.2. The protection zones of single rod lightning rods of 150 m high-rise buildings have the following overall dimensions.

2. Double rod lightning rod.

2.1. Protection zone of double rod lightning rod with height h ≤ 150 m shown in Fig. P3.2. The end areas of the protection zone are defined as zones of single rod lightning rods, the overall dimensions of which h 0 , r 0 , r x1 , r x2 are determined according to the formulas of clause 1.1 of this appendix for both types of protection zones.

Rice. P3.2. Protection zone of double rod lightning rod:
1 - border of the protection zone at level h x1; 2 - the same at level h x2,
3 - same at ground level

The internal areas of the protection zones of the double rod lightning rod have the following overall dimensions.

With a distance between lightning rods L >

When the distance between lightning rods is L > 6h, to construct zone B, the lightning rods should be considered as single.

With known values ​​of h c and L (at r cx = 0), the height of the lightning rod for zone B is determined by the formula

h = (h c + 0.14L) / 1.06.

2.2. Protection zone of two lightning rods different heights h 1 and h 2 ≤ 150 m shown in Fig. PZ.Z. The overall dimensions of the end areas of the protection zones h 01, h 02, r 01, r 02, r x1, r x2 are determined according to the formulas of clause 1.1, as for the protection zones of both types of a single lightning rod. The overall dimensions of the internal area of ​​the protection zone are determined by the formulas:

where the values ​​of h c1 and h c2 are calculated using the formulas for h c in clause 2.1 of this appendix.

For two lightning rods of different heights, the construction of zone A of a double rod lightning rod is carried out at L ≤ 4h min, and zone B - at L ≤ 6h min. With correspondingly large distances between lightning rods, they are considered as single.

Rice. PZ.Z Zone protected by two lightning rods of different heights. The designations are the same as in Fig. P3.1

3. Multiple lightning rod.

The protection zone of a multiple lightning rod (Fig. A3.4) is defined as the protection zone of paired adjacent lightning rods with a height h ≤ 150 m(see clauses 2.1, 2.2 of this appendix).

Rice. P3.4. Protection zone (in plan) of a multiple lightning rod. The designations are the same as in Fig. P3.1

The main condition for the protection of one or several objects of height h x with a reliability corresponding to the reliability of zone A and zone B is the fulfillment of the inequality r cx > 0 for all lightning rods taken in pairs. Otherwise, the construction of protection zones must be carried out for single or double lightning rods, depending on the fulfillment of the conditions of clause 2 of this appendix.

4. Single cable lightning rod.

Protection zone of a single cable lightning rod with a height of h≤150 m shown in Fig. A3.5, where h is the height of the cable in the middle of the span. Taking into account the sag of a cable with a cross section of 35–50 mm 2 with a known height of supports h op and span length a, the height of the cable (in meters) is determined:

h = h op - 2 at a m;

h = h op - 3 at 120 m.

Rice. P3.5. Protection zone of a single cable lightning rod. The designations are the same as in Fig. P3.1

The protection zones of a single cable lightning rod have the following overall dimensions.

When the distance between cable lightning rods is L > 4h, to construct zone A, the lightning rods should be considered as single.

When the distance between cable lightning rods is L > 6h, to construct zone B, the lightning rods should be considered as single. With known values ​​of h c and L (at r cx = 0), the height of the cable lightning rod for zone B is determined by the formula

h = (h c + 0.12L) / 1.06.

Rice. P3.7. Protection zone of two cable lightning rods of different heights

5.2. The protection zone of two cables of different heights h 1 and h 2 is shown in Fig. P3.7. The values ​​of r 01 , r 02 , h 01 , h 02 , r x1 , r x1 are determined according to the formulas of paragraph 4 of this appendix as for a single cable lightning rod. To determine the sizes r c and h c the following formulas are used:

where h c1 and h c1 are calculated using the formulas for hc A.5.1 of this appendix.

APPENDIX 4

MANUAL FOR "INSTRUCTIONS FOR LIGHTNING PROTECTION OF BUILDINGS AND STRUCTURES" (RD34.21.122-87)

This manual aims to explain and specify the main provisions of RD 3421.122-87, as well as to familiarize specialists involved in the development and design of lightning protection of various objects with existing ideas about the development of lightning and its parameters that determine the dangerous effects on humans and material values. Examples are given of the implementation of lightning protection of buildings and structures of various categories in accordance with the requirements of RD 34.21.122-87.

1. BRIEF INFORMATION ABOUT LIGHTNING DISCHARGES AND THEIR PARAMETERS

Lightning is an electrical discharge several kilometers long that develops between a thundercloud and the ground or some ground structure.

A lightning discharge begins with the development of a leader - a weakly glowing channel with a current of several hundred amperes. According to the direction of movement of the leader - from the cloud downwards or from the ground structure upwards - lightning is divided into downward and upward. Data on downward lightning have been accumulated for a long time in several regions of the globe. Information about ascending lightning appeared only in recent decades, when systematic observations of the lightning susceptibility of very tall structures, for example the Ostankino television tower, began.

The leader of downward lightning appears under the influence of processes in a thundercloud, and its appearance does not depend on the presence of any structures on the surface of the earth. As the leader moves toward the ground, counter leaders directed toward the cloud can be excited from ground objects. The contact of one of them with the downward leader (or the latter touching the surface of the earth) determines the location of the lightning strike into the ground or some object.

Rising leaders are excited from high grounded structures, at the tops of which the electric field sharply increases during a thunderstorm. The very fact of the emergence and sustainable development of a rising leader determines the location of defeat. On flat terrain, ascending lightning strikes objects with a height of more than 150 m, and in mountainous areas they are excited from pointed relief elements and structures of lower height and are therefore observed more often.

Let us first consider the development process and parameters of downward lightning. After the establishment of a through leader channel, the main stage of the discharge follows - rapid neutralization of the leader's charges, accompanied by a bright glow and an increase in current to peak values ​​ranging from a few to hundreds of kiloamperes. In this case, intense heating of the channel occurs (up to tens of thousands of Kelvin) and its shock expansion, which is perceived by ear as a clap of thunder. The main stage current consists of one or more successive pulses superimposed on a continuous component. Most current pulses have negative polarity. The first pulse with a total duration of several hundred microseconds has a front length from 3 to 20 mks; the peak current value (amplitude) varies widely: in 50% of cases (average current) exceeds 30, and in 1-2% of cases 100 kA. In approximately 70% of downward negative lightning, the first pulse is followed by subsequent ones with smaller amplitudes and front length: the average values ​​are 12 kA and 0.6 mks. In this case, the slope (rate of rise) of the current at the front of subsequent pulses is higher than for the first pulse.

The current of the continuous component of downward lightning varies from a few to hundreds of amperes and exists throughout the entire flash, lasting an average of 0.2 With, and in rare cases 1-1.5 With.

The charge transferred during the entire lightning flash ranges from units to hundreds of coulombs, of which the individual pulses account for 5-15, and the continuous component accounts for 10-20 Cl.

Downward lightning with positive current pulses is observed in approximately 10% of cases. Some of them have a shape similar to that of negative impulses. In addition, positive pulses with significantly larger parameters were recorded: a duration of about 1000 mks, front length about 100 mks and transferable charge on average 35 Cl. They are characterized by variations in current amplitudes over a very wide range: with an average current of 35 kA in 1-2% of cases, amplitudes over 500 may appear kA.

The accumulated actual data on the parameters of downward lightning do not allow us to judge their differences in different geographical regions. Therefore, for the entire territory of the USSR, their probabilistic characteristics are assumed to be the same

Rising lightning develops as follows. After the ascending leader has reached the thundercloud, the discharge process begins, accompanied in approximately 80% of cases by currents of negative polarity. Currents of two types are observed: the first is continuous, pulseless up to several hundred amperes and lasting tenths of a second, carrying a charge of 2-20 Cl; the second is characterized by the superposition of short pulses on the long-term pulseless component, the amplitude of which is on average 10-12 kA and only in 5% of cases exceeds 30 kA, and the transferred charge reaches 40 Cl. These impulses are similar to the subsequent impulses of the main stage of downward negative lightning.

In mountainous areas, upward lightning is characterized by longer continuous currents and larger transferred charges than on the plain. At the same time, variations in the pulse components of the current in the mountains and on the plain differ little. To date, no connection has been identified between ascending lightning currents and the height of the structures from which they are excited. Therefore, the parameters of ascending lightning and their variations are assessed as the same for any geographic regions and object heights.

In RD 34.21.122-87, data on the parameters of lightning currents are taken into account in the requirements for the designs and sizes of lightning protection means. For example, the minimum permissible distances from lightning rods and their grounding conductors to objects of category I (clauses 2.3—2.5 *) are determined from the condition that lightning rods are damaged by downward lightning with the amplitude and slope of the current front within the limits of 100, respectively. kA and 50 kA/μs. This condition is met in at least 99% of cases of damage by downward lightning.

2. CHARACTERISTICS OF LIGHTNING ACTIVITY

The intensity of thunderstorm activity in various geographic locations can be judged from data from an extensive network of meteorological stations on the frequency and duration of thunderstorms, recorded in days and hours per year by the audible thunder at the beginning and end of a thunderstorm. However, a more important and informative characteristic for assessing the possible number of lightning strikes on objects is the density of downward lightning strikes per unit of earth's surface.

The density of lightning strikes to the ground varies greatly across regions of the globe and depends on geological, climatic and other factors. With a general tendency for this value to increase from the poles to the equator, it, for example, sharply decreases in deserts and increases in regions with intense evaporation processes. The influence of relief is especially great in mountainous areas, where thunderstorm fronts predominantly spread along narrow corridors, therefore, within a small area, sharp fluctuations in the density of discharges into the ground are possible.

In general, across the globe, the density of lightning strikes varies from almost zero in the polar regions to 20-30 strikes per 1 km land per year in humid tropical zones. For the same region, variations are possible from year to year, therefore, for a reliable assessment of the density of discharges into the ground, long-term averaging is necessary.

Currently, a limited number of locations around the globe are equipped with lightning counters, and for small areas, direct estimates of the density of discharges into the ground are possible. On a mass scale (for example, for the entire territory of the USSR), recording the number of lightning strikes into the ground is not yet feasible due to labor intensity and lack of reliable equipment.

However, for geographic locations where lightning counters are installed and meteorological observations of thunderstorms are carried out, a correlation has been found between the density of discharges into the ground and the frequency or duration of thunderstorms, although each of these parameters is subject to variation from year to year or from thunderstorm to thunderstorm. In RD 34.21.122-87, this correlation dependence, presented in Appendix 2, is extended to the entire territory of the USSR and connects purely downward lightning strikes to 1 km 2 the earth's surface with a specific duration of thunderstorms in hours. Data from meteorological stations on the duration of thunderstorms are averaged over the period from 1936 to 1978 and are plotted in the form of lines characterized by a constant number of thunderstorm hours per year. geographical map USSR (Fig. 3 RD 34.21.122-87); in this case, the duration of a thunderstorm for any point is set in the interval between the two lines closest to it. For some regions of the USSR, on the basis of instrumental research, regional maps of the duration of thunderstorms have been compiled, these maps are also recommended for use (see Appendix 2 RD34.21.122-87)

In this indirect way (through data on the duration of thunderstorms) it is possible to introduce zoning of the territory of the USSR according to the density of lightning strikes into the ground

3. NUMBER OF LIGHTNING DAMAGES ON GROUND STRUCTURES

According to the requirements of table. 1 RD 34.21.122-87 for a number of objects the expected number of lightning strikes is an indicator that determines the need for lightning protection and its reliability. Therefore, it is necessary to have a way to evaluate this value at the design stage of the facility. It is desirable that this method take into account known characteristics of thunderstorm activity and other information about lightning.

When calculating the number of strikes by downward lightning, the following concept is used: a towering object receives discharges that, in its absence, would strike the surface of the earth of a certain area (the so-called contraction surface). This area has the shape of a circle for a concentrated object (a vertical pipe or tower) and the shape of a rectangle for an extended object, such as an overhead power line. The number of hits on an object is equal to the product of the contraction area and the density of lightning discharges plus its location. For example, for a concentrated object

where R 0 is the contraction radius; n - average annual number of lightning strikes in 1 km 2 earth's surface. For an extended object with length l

The available statistics of damage to objects of different heights in areas with different durations of thunderstorms made it possible to roughly determine the relationship between the contraction radius R0 and the height of the object h. Despite the significant scatter, on average we can take R 0 = 3h.

The given ratios are the basis for the formulas for calculating the expected number of lightning strikes on concentrated objects and objects with given dimensions in Appendix 2 of RD 34.21.122-87. The lightning damage of objects is directly dependent on the density of lightning discharges into the ground and, accordingly, on the regional duration of thunderstorms in accordance with the data in Appendix 2. It can be assumed that the probability of damage to an object increases, for example, with increasing amplitude of the lightning current, and depends on other parameters of the discharge. However, the available statistics of damage were obtained in ways (by photographing lightning strikes, recording with special meters) that do not allow us to isolate the influence of factors other than the intensity of thunderstorm activity.

Let us now estimate, using the formulas in Appendix 2, how often objects can be struck by lightning different sizes and shapes. For example, with an average duration of thunderstorms of 40–60 h per year into a concentrated object with a height of 50 m(for example, a chimney) no more than one lesion can be expected in 3-4 years, and in a building 20 m and dimensions in terms of 100x100 m (typical in size for many types of production) - no more than one lesion in 5 years. Thus, with moderate sizes of buildings and structures (height within 20-50 m, length and width approximately 100 m) being struck by lightning is a rare event. For small buildings (with dimensions of approximately 10 m) the expected number of lightning strikes rarely exceeds 0.02 per year, which means that no more than one lightning strike can occur during their entire service life. For this reason, according to RD 34.21.122-87, for some small buildings (even with low fire resistance), lightning protection is not provided at all or is significantly simplified.

For concentrated objects, the number of damage from downward lightning increases quadratically with height and in areas with moderate duration of thunderstorms at object heights of about 150 m amounts to one or two hits per year. From concentrated objects of greater height, ascending lightning is excited, the number of which is also proportional to the square of the height. This idea of ​​​​the susceptibility of high objects is confirmed by observations carried out on the Ostankino television tower with a height of 540 m: every year there are about 30 lightning strikes and more than 90% of them are from upward strikes, the number of strikes from downward lightning remains at one or two per year. Thus, for concentrated objects with a height of more than 150 m the number of strikes by downward lightning depends little on height.

4. HAZARDOUS EFFECTS OF LIGHTNING

The list of basic terms (Appendix 1 RD 34.21.122-87) lists possible types of lightning effects on various ground objects. In this paragraph, information about the dangerous effects of lightning is presented in more detail.

The effects of lightning are usually divided into two main groups:

primary, caused by a direct lightning strike, and secondary, induced by nearby lightning discharges or carried into the object by extended metal communications. The danger of a direct strike and secondary effects of lightning for buildings and structures and the people or animals in them is determined, on the one hand, by the parameters of the lightning discharge, and on the other hand, by the technological and design characteristics of the object (presence of fire or fire hazard zones, fire resistance of building structures, type input communications, their location inside the object, etc.). A direct lightning strike causes the following effects on an object: electrical, associated with electric shock to people or animals and the appearance of overvoltage on the affected elements. The overvoltage is proportional to the amplitude and slope of the lightning current, the inductance of structures and the resistance of the grounding conductors through which the lightning current is discharged into the ground. Even with lightning protection, direct lightning strikes with high currents and steepness can lead to overvoltages of several megavolts. In the absence of lightning protection, the paths of lightning current spreading are uncontrollable and its strike can create a danger of electric shock, dangerous step and touch voltages, and overlap to other objects;

thermal, associated with a sharp release of heat during direct contact of the lightning channel with the contents of the object and when lightning current flows through the object. The energy released in the lightning channel is determined by the transferred charge, the duration of the flash and the amplitude of the lightning current; and 95% of cases of lightning discharges this energy (calculated on resistance 1 Ohm) exceeds 5.5 J, it is two to three orders of magnitude higher than the minimum ignition energy of most gas, steam and dust-air mixtures used in industry. Consequently, in such environments, contact with the lightning channel always creates a danger of ignition (and in some cases, explosion), the same applies to cases of lightning channel penetration of the housings of explosive outdoor installations. When lightning current flows through thin conductors, there is a danger of them melting and breaking;

mechanical, caused by a shock wave propagating from the lightning channel, and electrodynamic forces acting on conductors with lightning currents. This impact can cause, for example, thin metal tubes to flatten. Contact with a lightning channel can cause sudden vapor or gas formation in some materials, followed by mechanical destruction, such as splitting wood or cracking concrete.

Secondary manifestations of lightning are associated with the effect of close discharges on the object of the electromagnetic field. This field is usually considered in the form of two components: the first is due to the movement of charges in the lightning leader and channel, the second is due to the change in lightning current over time. These components are sometimes called electrostatic and electromagnetic induction.

Electrostatic induction manifests itself in the form of overvoltage that occurs on the metal structures of an object and depends on the lightning current, the distance to the strike site and the resistance of the ground electrode. In the absence of a proper grounding system, overvoltage can reach hundreds of kilovolts and create a danger of injury to people and overlaps between different parts of the facility.

Electromagnetic induction is associated with the formation of an EMF in metal circuits, proportional to the steepness of the lightning current and the area covered by the circuit. Extended communications in modern industrial buildings can form circuits covering a large area, in which it is possible to induce an EMF of several tens of kilovolts. In places where extended metal structures come together, in gaps in open circuits, there is a danger of overlaps and sparks with possible energy dissipation of about tenths of a joule.

Another type of dangerous impact of lightning is the introduction of high potential through communications introduced into the facility (overhead power lines, cables, pipelines). It is an overvoltage that occurs on communications during direct and close lightning strikes and spreads in the form of a wave impinging on the object. The danger is created due to possible overlaps from communications to grounded parts of the facility. Underground communications also pose a danger, since they can absorb part of the lightning currents spreading in the ground and carry them into the facility.

5. CLASSIFICATION OF PROTECTED OBJECTS

The severity of the consequences of a lightning strike depends primarily on the explosion or fire hazard of a building or structure due to the thermal effects of lightning, as well as sparks and flashovers caused by other types of impacts. For example, in industries that are constantly associated with open fire, combustion processes, and the use of fireproof materials and structures, the flow of lightning current does not pose a great danger. On the contrary, the presence of an explosive atmosphere inside the object will create the threat of destruction, human casualties, and large material damage.

With such diversity technological conditions making the same requirements for lightning protection of all objects would mean either investing excessive reserves in it, or putting up with the inevitability of significant damage caused by lightning. Therefore, RD 34.21.122-87 adopted a differentiated approach to lightning protection of various objects, and therefore in Table. 1 of this Instruction, buildings and structures are divided into three categories, differing in severity possible consequences lightning damage.

Category I included industrial premises, in which, under normal technological conditions, explosive concentrations of gases, vapors, dusts, and fibers can occur and form. Any lightning strike, causing an explosion, creates an increased danger of destruction and casualties not only for this object, but also for nearby

Category II includes industrial buildings and structures in which the appearance of an explosive concentration occurs as a result of a violation of the normal technological regime, as well as external installations containing explosive liquids and gases. For these objects, a lightning strike creates a danger of explosion only when it coincides with a technological accident or the activation of breathing or emergency valves in outdoor installations. Due to the moderate duration of thunderstorms on the territory of the USSR, the likelihood of these events coinciding is quite low.

Category III includes objects whose consequences are associated with less material damage than in an explosive environment. This includes buildings and structures with fire-hazardous premises or building structures of low fire resistance, and for them the requirements for lightning protection are tightened with an increase in the probability of damage to the object (the expected number of lightning strikes). In addition, category III includes objects whose damage poses a danger of electrical exposure to people and animals: large public buildings, livestock buildings, tall structures such as pipes, towers, monuments. Finally, category III includes small buildings in rural areas, where combustible structures are most often used. According to statistics, these objects account for a significant proportion of fires caused by thunderstorms. Due to the low cost of these buildings, their lightning protection is carried out using simplified methods that do not require significant material costs(clause 2.30).

6. MEANS AND METHODS OF LIGHTNING PROTECTION

Requirements for the implementation of the entire range of measures for lightning protection of objects of categories I, II and III and the designs of lightning rods are set out in § 2 and 3 of RD 34.21.122-87. This section of the manual explains the main provisions of these requirements.

Lightning protection is a set of measures aimed at preventing a direct lightning strike on an object or eliminating the dangerous consequences associated with a direct strike; This complex also includes protective equipment that protects the object from the secondary effects of lightning and the introduction of high potential.

A means of protection against direct lightning strikes is a lightning rod - a device designed for direct contact with the lightning channel and discharging its current into the ground.

Lightning rods are divided into free-standing ones, which ensure the spread of lightning current bypassing the object, and installed on the object itself. In this case, the current spreads along controlled paths so that there is a low probability of injury to people (animals), explosion or fire.

Installation of free-standing lightning rods eliminates the possibility of thermal impact on the object when the lightning rod is struck; For objects with a constant risk of explosion, classified as category I, this method of protection has been adopted, ensuring a minimum number of dangerous impacts during a thunderstorm. For objects of categories II and III, characterized by a lower risk of explosion or fire, the use of free-standing lightning rods and those installed on the protected object is equally permissible.

The lightning rod consists of the following elements: lightning rod, support, down conductor and grounding conductor. However, in practice they can form a single structure, for example, a metal mast or truss of a building is an air terminal, a support and a down conductor at the same time.

Based on the type of lightning rod, lightning rods are divided into rod (vertical), cable (horizontal extended) and meshes consisting of longitudinal and transverse horizontal electrodes connected at intersections. Rod and cable lightning rods can be either free-standing or installed on site; lightning protection meshes are laid on metal roofing protected buildings and structures. However, laying nets is rational only on buildings with horizontal roofs, where any part of them is equally likely to be struck by lightning. With large roof slopes, lightning strikes are most likely near the ridge, and in these cases, laying mesh over the entire roof surface will lead to unjustified metal costs; It is more economical to install rod or cable lightning rods, the protection zone of which includes the entire facility. For this reason, in clause 2.11, laying lightning protection mesh is allowed on non-metallic roofs with a slope of no more than 1:8. Sometimes laying the mesh over the roof is inconvenient due to its structural elements (for example, the wavy surface of the covering). In these cases, it is allowed to lay the mesh under the insulation or waterproofing, provided that they are made of fireproof or fire-resistant materials and their breakdown during a lightning discharge will not lead to the roof catching fire (clause 2.11).

When choosing means of protection against direct lightning strikes and types of lightning rods, it is necessary to take into account economic considerations, technological and design features of objects. In all possible cases, nearby high structures must be used as free-standing lightning rods, and structural elements of buildings and structures, such as metal roofing, trusses, metal and reinforced concrete columns and foundations, as lightning rods, down conductors and grounding conductors. These provisions are taken into account in paragraphs. 1.6, 1.8, 2.11, 2.12, 2.25. Protection from the thermal effects of a direct lightning strike is carried out by proper selection of the cross-sections of lightning rods and down conductors (Table 3), the thickness of the casings of external installations (clause 2.15), melting and penetration of which cannot occur with the above parameters of lightning current, transferred charge and temperature in channel.

Protection against mechanical destruction of various building structures during direct lightning strikes is carried out: concrete - by reinforcement and provision of reliable contacts at the points of connection with the reinforcement (clause 2.12); non-metallic protruding parts and coverings of buildings - using materials that do not contain moisture or gas-generating substances.

Protection against flashovers to the protected object in the event of damage to free-standing lightning rods is achieved by proper selection of grounding conductor designs and insulating distances between the lightning rod and the object (clauses 2.2 - 2.5). Protection against overlaps inside a building when lightning current flows through it is ensured by an appropriate choice of the number of down conductors laid to the grounding conductors along the shortest paths (clause 2.11).

Protection against touch and step voltages (clauses 2.12, 2.13) is ensured by laying down conductors in places inaccessible to people and uniformly placing grounding conductors throughout the facility.

Protection against secondary effects of lightning is ensured by the following measures. From electrostatic induction and the introduction of high potential - by limiting overvoltages induced on equipment, metal structures and input communications, by connecting them to ground electrodes of certain designs; from electromagnetic induction - by limiting the area of ​​open circuits inside buildings by placing jumpers in places where metal communications come together. To avoid sparking at the junctions of extended metal communications, low transition resistances are ensured - no more than 0.03 Ohm, for example, in flanged pipeline connections, this requirement is met by tightening six bolts on each flange (clause 2.7).

7. PROTECTIVE ACTION AND PROTECTION ZONES OF LIGHTNING DRIVES

Below we explain the approach to determining lightning rod protection zones, the construction of which is carried out according to the formulas of Appendix 3 of RD 34.21.122-87.

The protective effect of a lightning rod is based on the “property of lightning that is more likely to strike higher and well-grounded objects compared to nearby objects of lower height. Therefore, the lightning rod, rising above the protected object, is assigned the function of intercepting lightning, which in the absence of a lightning rod would strike the object. Quantitatively the protective effect of a lightning rod is determined through the probability of a breakthrough - the ratio of the number of lightning strikes to a protected object (the number of breakthroughs) to the total number of strikes to the lightning rod and the object.

There are several ways to assess the probability of a breakthrough, based on different physical concepts of the processes of lightning damage. RD 34.21.122-87 uses the results of calculations using a probabilistic technique that relates the probability of damage to a lightning rod and an object with the scattering of downward lightning trajectories without taking into account variations in its currents.

According to the adopted calculation model, it is impossible to create ideal protection against direct lightning strikes, completely excluding breakthroughs to the protected object. However, in practice it is feasible mutual arrangement object and lightning rod, providing a low probability of breakthrough, for example 0.1 and 0.01, which corresponds to a reduction in the number of damage to the object by approximately 10 and 100 times compared to an unprotected object. For most modern facilities, such levels of protection ensure a small number of breakthroughs over their entire service life.

Above, we considered an industrial building with a height of 20 and dimensions in plan of 100 x 100 m, located in an area with a thunderstorm duration of 40-60 hours per year; If this building is protected by lightning rods with a breakthrough probability of 0.1, no more than one breakthrough can be expected into it in 50 years. However, not all breakthroughs are equally dangerous for the protected object; for example, ignition is possible at high currents or transferred charges, which are not found in every lightning discharge. Consequently, a given facility can be expected to experience one hazardous impact over a period obviously exceeding 50 years, or for most industrial facilities of categories II and III, no more than one hazardous impact during the entire period of their existence. With a breakout probability of 0.01, the same building can expect no more than one breakout in 500 years—a period far longer than the lifespan of any industrial facility. Such a high level of protection is justified only for category I objects that pose a constant threat of explosion.

By performing a series of calculations of the probability of a breakthrough in the vicinity of a lightning rod, it is possible to construct a surface that is the geometric location of the vertices of protected objects for which the probability of a breakthrough is a constant value. This surface is the outer boundary of the space called the lightning protection zone; for a single rod lightning rod this boundary is the lateral surface of a circular cone, for a single cable it is a gable flat surface.

Typically, a protection zone is designated by the maximum probability of a breakthrough corresponding to its outer boundary, although in the depths of the zone the probability of a breakthrough decreases significantly.

The calculation method makes it possible to construct a protection zone for rod and cable lightning rods with an arbitrary value of the probability of a breakthrough, i.e. for any lightning rod (single or double), you can build an arbitrary number of protection zones. However, for most commercial buildings, a sufficient level of protection can be ensured by using two zones, with a breakthrough probability of 0.1 and 0.01.

In terms of reliability theory, the probability of a breakthrough is a parameter characterizing the failure of a lightning rod as a protective device. With this approach, the two accepted protection zones correspond to a reliability degree of 0.9 and 0.99. This reliability assessment is valid when the object is located near the border of the protection zone, for example, an object in the form of a ring coaxial with a lightning rod. For real objects (ordinary buildings) on the border of the protection zone, as a rule, only the upper elements are located, and most of the object is placed deep in the zone. Assessing the reliability of the protection zone along its outer border leads to excessively underestimated values. Therefore, in order to take into account the relative position of lightning rods and objects that exists in practice, protection zones A and B are assigned in RD 34.21.122-87 an approximate degree of reliability of 0.995 and 0.95, respectively.

Linear dependencies between the calculated parameters of type B protection zones make it possible to estimate the heights of lightning rods with sufficient accuracy for practice using nomograms that reduce the amount of calculations. Such nomograms, constructed in accordance with the formulas and notations of Appendix 3 of RD 34.21.122-87, are shown in Fig. P4.1 for determining the heights of rod C and cable T of single and double lightning rods (developed by Giproprom).

Rice. P4.1. Nomograms for determining the height of single (a) and double equal height(b) lightning rods in zone B

The breakthrough probability calculation method has been developed only for downward lightning, predominantly striking objects up to 150 m high. m. Therefore, in RD 34.21.122 - 87, formulas for constructing protection zones for single and multiple rod and cable lightning rods are limited to a height of 150 m. To date, the volume of actual data on the susceptibility of objects of greater height to downward lightning is very small and mostly relates to the Ostankino television tower. Based on photographic recordings, it can be argued that downward lightning breaks more than 200 m below its top and strikes the ground at a distance of about 200 m from the base of the tower. If we consider the Ostankino television tower as a rod lightning rod, we can conclude that the relative sizes of the protection zones of lightning rods with a height of more than 150 m sharply decrease with increasing height of lightning rods. Taking into account the limited actual data on the susceptibility of ultra-tall objects, RD 34.21.122 - 87 includes formulas for constructing protection zones only for rod lightning rods with a height of more than 150 m.

A method for calculating protection zones against rising lightning has not yet been developed. However, according to observational data, it is known that ascending discharges are excited from pointed objects near the top of tall structures and impede the development of other discharges with more low levels. Therefore, for such high objects as reinforced concrete chimneys or towers, protection is provided first of all from mechanical destruction of concrete when excited by upward lightning, which is carried out by installing rod or ring lightning rods that provide the maximum possible, for design reasons, excess above the top of the object (clause 2.31) .

8. APPROACH TO STANDARDING LIGHTNING PROTECTION EARTHING TERMS

The approach to the selection of grounding conductors for lightning protection of buildings and structures, adopted in RD 34.21.122-87, is explained below.

One of effective ways limiting lightning overvoltages in the lightning rod circuit, as well as on metal structures and equipment of the facility, is to ensure low grounding resistances. Therefore, when choosing lightning protection, the resistance of the ground electrode or its other characteristics related to resistance are subject to standardization.

Until recently, the impulse resistance to the spreading of lightning currents was standardized for lightning protection grounding conductors: its maximum permissible value was taken equal to 10 Ohm for buildings and structures of categories I and II and 20 Ohm for buildings and structures of category III. In this case, it was allowed to increase the pulse resistance to 40 Ohm in soils with a resistivity of more than 500 Ohm m while simultaneously removing lightning rods from objects of category I at a distance that guarantees against breakdown in the air and in the ground. For outdoor installations, the maximum permissible impulse resistance of grounding conductors was taken to be 50 Ohm.

The impulse resistance of the ground electrode is a quantitative characteristic of complex physical processes during the spreading of lightning currents in the ground. Its value differs from the resistance of the grounding conductor during the spreading of industrial frequency currents and depends on several parameters of the lightning current (amplitude, slope, front length), varying within wide limits. With an increase in lightning current, the pulse resistance of the ground electrode drops, and in the possible distribution range of lightning currents (from units to hundreds of kiloamperes) its value can decrease by 2-5 times.

When designing a ground electrode, it is impossible to predict the values ​​of lightning currents that will flow through it, and therefore, it is impossible to estimate in advance the corresponding values ​​of impulse resistances. Under these conditions, standardizing grounding conductors by their impulse resistance has obvious inconveniences. It's wiser to choose concrete designs grounding conductors according to the following condition. The impulse resistance of grounding conductors in the entire possible range of lightning currents should not exceed the specified maximum permissible values.

This standardization was adopted in paragraphs. 2.2, 2.13, 2.26, table. 2: for a number of standard designs, impulse resistances were calculated when lightning currents fluctuated from 5 to 100 kA and based on the calculation results, a selection of grounding conductors that satisfy the accepted condition was carried out.

Currently, reinforced concrete foundations are common and recommended (RD 34.21.122-87, clause 1.8) grounding structures. They are subject to an additional requirement - the exclusion of mechanical destruction of concrete when lightning currents spread through the foundation. Reinforced concrete structures can withstand high densities of lightning currents spreading over the reinforcement, which is associated with the short duration of this spreading. Single reinforced concrete foundations (piles with a length of at least 5 or footings with a length of at least 2 m) are capable of withstanding lightning currents up to 100 without destruction kA, according to this condition in table. 2 RD 34.21.122-87 specifies the permissible dimensions of individual reinforced concrete grounding conductors. For large foundations with a correspondingly larger reinforcement surface, a current density dangerous for concrete destruction is unlikely to occur at any possible lightning currents.

Normalizing the parameters of grounding conductors according to their standard designs has a number of advantages: it corresponds to the standardization of reinforced concrete foundations accepted in construction practice, taking into account their widespread use as natural grounding conductors; when choosing lightning protection, it is not necessary to perform calculations of the pulse resistance of grounding conductors, which reduces the volume design work.

9. EXAMPLES OF LIGHTNING PROTECTION FOR VARIOUS OBJECTS* (FIG. P4.2-P4.E)

* Developed by VNIPI Tyazhpromepsktroproekt, Giprotruboprovod Institute and GIAP,

Rice. P4.2. Lightning protection of a category I building with a free-standing double rod lightning rod (ρ = 300 Ohm m, S in ≤ 4 m, S z ≤ 6 m):

1 — border of the protection zone; 2 - foundation grounding conductors; 3 - protection zone at 8.0 m

Rice. P4.3. Lightning protection of a category I building with a separate catenary lightning rod (ρ = 300 Ohm m, S â ≤ 4 m, S z ≤ 6 m, S in1 ≥ 3.5 m):

1 - cable; 2 — border of the protection zone; 3 - entry of underground pipeline; 4—limit of distribution of explosive concentration; 5—reinforcement connections made by welding; 6 - reinforced concrete foundation; 7 — embedded elements for connecting equipment; 8 - grounding conductor made of steel 4×40 mm; 9 - grounding conductors - reinforced concrete footrests; 10 — border of the protection zone at 10.5

Figure P4.4. Lightning protection of a category II building with a mesh laid on the roof under waterproofing:

1 - lightning protection mesh; 2 - waterproofing of the building; 3 - building support; 4 — steel jumper; 5 - column reinforcement; 6 - grounding conductors, reinforced concrete foundations; 7 - embedded part; 8 — overpass support; 9 - technological overpass

Rice. P4.5. Lightning protection of a category II building with metal trusses (reinforced concrete columns and foundations are used as down conductors and grounding conductors):

1 - column reinforcement; 2 - foundation reinforcement; 3 - ground electrode; 4 - steel truss; 5 - reinforced concrete column; 6 - anchor bolts welded to the reinforcement; 7 - embedded part

Rice. P4.6. Layout of the nitrogen-hydrogen mixture compression workshop (classified as explosive with class B-1a zone):

Legend: — rod lightning rod (No. 1-6); —.—.—.- current-carrying metal strip; — gas outlet pipes for venting gases of non-explosive concentrations into the atmosphere; - the same explosive concentration

Fig, P4.7. Lightning protection of a metal tank with a capacity of 20 thousand. m 3 with spherical roof:

1 - breathing valve; 2 - area of ​​release of gases of explosive concentration; 3 — border of the protection zone; 4 - protection zone at height h x = 23.7 m; 5 - the same at height h x =22.76 m

Rice. P4.8. Lightning protection of a metal tank with a capacity of 20 thousand m3 with a spherical roof and pontoon:

1 — emergency gas release valve; 2, 3 - the same as in Fig. 4.7; 4 - pontoon; 5 — protection zone at height hх = 23 m; 6 - flexible cable

Rice. P4.9. Lightning protection of a rural house with a cable lightning rod installed on the roof:

1 — cable lightning rod; 2 — input of an overhead power line (VL) and grounding of the VL hooks on the wall; 3 — down conductor; 4 - ground electrode

What is lightning, we know from school desk. An electric discharge with a power of 100-200 thousand amperes destroys all objects where it hits. Most likely, lightning is attracted by tall buildings and trees.

Lightning protection of a private home is more relevant today than ever. Our homes are literally filled with electronics, household appliances, and mobile phones, which increases the risk of lightning exposure. The danger of lightning for private homes, those not equipped with lightning rods are great - fire, destruction in the event of a direct hit by a discharge. The consequences of a discharge in the immediate vicinity of a building may be the failure of the electrical network or a separate device - a TV, computer, etc.

• Internal, protecting against a discharge that does not fall directly into the house, but, for example, into the power line feeding the internal wiring. In this case, an overvoltage occurs in the electrical network, the consequences of which can be disastrous. The internal protection is not visible; it is a small device - a limiter, a surge arrester, an SPD installed in the distribution board.
• External protection is the familiar lightning rod (as lightning protection is often incorrectly called) installed on the roof.

External protection of a private house from lightning

The system can be passive or active. The principle of operation of the first is simple, like everything ingenious. A metal lightning rod on the roof catches (attracts, intercepts) a lightning discharge and, through a current conductor, directs it to the ground, to the ground electrode.

Active lightning protection

Such lightning protection is more effective; it operates within a radius of 100 meters from a “cunning” lightning rod, which, by ionizing the surrounding air, intercepts a lightning discharge. Then it works like passive protection. The main advantage of the device is the lightning protection coverage of neighboring residential buildings and outbuildings over a fairly large area.

Types of external lightning protection for a home

Based on the type of design, there are modular-pin, cable and mesh lightning protection.

Pin

The pin system is called because of the lightning rod, which is installed in the highest part of the roof, and is a metal rod (pin). This design is suitable for lightning protection of a private house with a roof made of metal tiles or any other material.

Rosovaya

Installation of this type of protective device is allowed if the roof is slate or tiled, but not metal.

The lightning rod is a cable (thick wire, rod) stretched at a height of 0.3-0.5 m along the ridge of the house.

Mesh

The system is considered the most complex in terms of installation. It is made from wire rod with a diameter of 6-8 mm, which in the form of a grid with cells of 6x6 meters is laid over the entire roof area. At the intersection of horizontal and vertical rods, it is welded. It is attached to the roof with brackets.

Mesh lightning protection for a house is installed, like cable lightning protection, on a slate or tiled roof.

Down conductor

For this element of the system, round steel (copper, aluminum) with a diameter of at least 6 mm is used. The down conductor is secured with brackets along the roof and walls. Usually during installation they try to lay the “route” away from window and doorways, as required by regulatory documents, and so as not to spoil the exterior of the building.

When laying a conductor, you need to follow some simple rules:

• On wooden surfaces The conductor should be mounted at a distance of 15-20cm from the wall;
• If a long-length cable receiver, a large-area mesh receiver or a pin receiver consists of several elements, then there must be several down conductors (CO 153-34.21. 122-2003)

When constructing a new structure, lightning protection of a cottage or house is already included in the design documentation. But if Vacation home or a country house has just been purchased and there is no “lightning rod” on it, then the most reasonable solution would be to protect yourself and your loved ones from lightning strikes yourself, or with the help of hired specialists.

If you have the skills to perform construction work, lightning protection of a private house with your own hands will not be a problematic issue, but will save money.

Ground loop

The principle of the ground electrode device is extremely simple. Three steel module pins 1.5-2 meters long, 16-20 mm in diameter with zinc coating, are driven into the ground and connected in series.

This design has a number of advantages:

• Possibility of installation to any depth without the use of special equipment;
• Low labor intensity. The work can be done by one person;
• The greater depth of immersion of the electrode pin increases the efficiency of grounding;
• The connection of elements does not require welding (using special clamps);
• The entire system is hidden underground.

The circuit is driven into the ground no closer than 1 m to the foundation of the house, and no closer than 5 m to the front door.

The principle of operation of internal lightning protection of a house

It is difficult to imagine life today without electronic and household electrical devices and instruments. All this equipment is connected to the power grid, and cables also go from the computer and TV to local network and satellite dish.

Data transmission lines through receivers, servers, distribution devices, power lines are susceptible to lightning strikes and the influence of electromagnetic fields. Under certain circumstances, high voltage and high current move through the cables to a low potential, i.e. TV, refrigerator, computer. The result may be failure of electrical appliances, fire, or threat to human life.

To protect yourself and your home, you need internal organization lightning protection of a private home or surge protection.

Such protection operates simply - it instantly equalizes the potentials between the electrical conductors. This task is performed by an SPD - a special surge protection device.

Installation of this device is only possible after installing a reliable external protection. To implement a lightning protection system for a private home, a project is being developed that takes into account all the ways to enter a high-voltage building.

After installing the SPD, non-current-carrying elements are connected to the grounding bus, and lines that cannot be grounded are connected to the bus through the SPD.

To select an SPD device, there are rules that can be divided into groups depending on:

• Indicators of the protected network - current, voltage, frequency, wire cross-section;
• Network type - power supply, cable TV, telephone line, alarm system, etc.;
• The significance of the protected object - PC, TV or bank server.

Do you need lightning protection for a private home?

The answer can be unequivocal - it is necessary! There are still many unknowns in the world, especially the mysteries of nature. If in a city a television tower or a high-rise building “protects” many surrounding houses from lightning, then in a private development area, as a rule, there are no such structures. But not far from the house there is a tall pine tree, which serves as a natural “lightning rod”. But this is a theory; it’s still better and calmer to feel safe in “your fortress.”

Lightning protection is a complex of various kinds of measures and means for their implementation, ensuring the safety of people, the safety of buildings and structures, equipment and materials from direct lightning strikes, electromagnetic and electrostatic induction, as well as from the introduction of high potentials through metal structures and communications.

Up to 16 million thunderstorms occur annually on the globe, i.e. about 44 thousand per day. At the same time, the expected number of lightning strikes per year of buildings and structures not equipped with lightning protection can be determined by the formula

N=10 -6 n[(a+6 h x)(b+6 h x)- 7.7h x 2 ],

Where P - the average number of lightning strikes 1 km 2 of the earth's surface per year, depending on the intensity of thunderstorm activity, varying within 2.5...7.5: for central Russia it can be accepted n = 5; a, b - respectively, the length and width of the protected building or structure, m; h x - height of the building (structure) along its sides, m.

For chimneys of boiler houses, water and silo towers, masts, trees and other objects, the expected number of lightning strikes per year is determined by the formula

N = 10 -6 πr 2 n,

where r is the equivalent radius, m: r= 3.5A; h- object height, m.

A direct lightning strike is very dangerous for people, buildings and structures due to the direct contact of the lightning channel with the affected objects. Losses from fires and explosions caused by this phenomenon alone are, in some cases, colossal. A direct lightning strike can also cause severe mechanical damage, most often rendering chimneys, masts, towers, and sometimes the walls of buildings unusable. At the same time, calculations show that the cost of implementing lightning protection measures is approximately 1.5 times less than the cost of buildings and structures that burned down over five years.

There are two main types of lightning: linear and ball.

Linear lightning is a discharge of atmospheric electricity between clouds or between clouds and the ground, occurring in ten-thousandths of a second, accompanied by thunder and the flow of current of tens of kiloamperes (in some cases up to 500 kA). The path of lightning is branched, since along its path there are sections of air with different properties, and the discharge always chooses the path of least resistance. As the discharge approaches the earth's surface, other factors begin to influence its further progress. Most often, the discharge rushes to elevated places on the ground (hills, etc.) or to tall buildings (chimneys, masts, etc.), where charges of the opposite sign (positive) are especially large.

The selectivity of the discharge is also affected by the electrical conductivity of the soil. It is not uncommon for lightning to directly hit the bottom of deep ravines with moist soil that has good electrical conductivity. Therefore, in hilly areas, rocky and sandy slopes are considered the safest, since the high electrical resistance of the soil in such places reduces the likelihood of lightning striking them. If a person is on a flat area during a thunderstorm, he should not walk, stand or sit near trees. In this case, it is safer to sit on a rock. When lightning strikes a car or tractor, people usually do not suffer because the metal cabin conducts the currents generated during the discharge past them and into the ground. A building with a non-metal roof that does not have a lightning rod does not always provide complete safety, since when lightning strikes a building of this type, discharges from the walls and roof inside the building are possible.

Ball lightning is relatively rare, about 300...500 times less common than linear lightning. It looks like a luminous ball, sometimes elongated in the shape of a pear. The temperature of ball lightning is 3000...5000 °C, the diameter is 10...20 cm, and the duration of existence is from fractions of a second to several minutes. It is capable of moving at speeds of up to 2 m/s, most often along a winding path and in most cases in the direction of the wind. When contacting ball lightning, severe burns occur on the human body, sometimes leading to death.

Ball lightning enters premises through open windows, doors, chimneys and even through small cracks or keyholes, and sometimes through electrical wiring. After a few moves it may disappear, but often ball lightning explodes, which leads to ignition of combustible objects, mechanical destruction and, in some cases, death.

Protection against linear lightning is often ineffective against ball lightning. Therefore, it is recommended to additionally close all windows, doors, chimneys, etc. during a thunderstorm, and ventilation grates provide grounded metal mesh, made of wire with a diameter of 2...2.5 mm, with cells with an area of ​​3...4 cm 2.

Depending on the significance of the object, the presence and class of explosion and fire hazardous zones in industrial buildings, as well as the likelihood of lightning damage, one of three categories of lightning protection is used (if required).

Lightning protection category II performed for production facilities with zones of classes B-Ia, B-I6 and B-IIa, provided that these zones occupy at least 30% of the entire building (if it is one-story) or the volume of the upper floor, as well as for open electrical installations with zones of class B -1g. Lightning protection of this category of these open installations mandatory throughout the Russian Federation, while for buildings it is required only in areas with thunderstorm activity of at least 10 hours per year. Objects protected from lightning under category II include flour mills and feed mills (workshops), ammonia refrigerators, liquid fuel and lubricant warehouses, separate rooms for charging and repairing batteries, fertilizer and pesticide warehouses, etc.

Lightning protection category II provides protection from direct lightning strikes, from the introduction of high potentials through overhead and underground communications, as well as from electrostatic and electromagnetic induction (induction of potentials in open metal circuits during the flow of pulsed lightning currents, creating the danger of sparks in places where these circuits come together) . To protect against electrostatic induction, metal cases and structures are grounded (zeroed), and against electromagnetic induction, metal jumpers are used between pipelines and similar extended objects (cable sheaths, etc.) in places where they come together at a distance of 10 cm or less at least every 25...30m. When installing category II lightning protection, overhead inputs of electrical lines, including telephone and radio, are replaced with a cable insert no less than 50 m long. The metal sheath of the cables at the entrance to the building and at the last support is connected to separate grounding devices that have resistance to the spreading of pulsed lightning current R and ≤10Ohm. Overpass pipelines are grounded in a similar way.

Lightning protection category III used for thunderstorm duration of 20 hours or more per year for outdoor installations of class P-III, buildings of III, IV degrees of fire resistance (kindergartens, nurseries, schools, etc.); hospitals, clubs and cinemas; vertical exhaust pipes of boiler houses or industrial enterprises, water and silo towers at a height of more than 15 m from the ground. If the duration of thunderstorms is 40 hours per year or more, then lightning protection of this category is required for livestock and poultry buildings of III...V degrees of fire resistance, as well as for residential buildings with a height of more than 30 m if they are located more than 400 m from general array.

Category III lightning protection eliminates dangerous and harmful factors that can arise from a direct lightning strike, and also protects against the introduction of high potentials into the building through overhead electrical lines and other overhead metal communications, such as pipelines. To this end

communications at the entrance to the building and at the nearest support are connected to grounding conductors with a resistance to the spreading of pulsed lightning current R and ≤ 20 Ohm. Containers with fuel and lubricants (except gasoline), chimneys and towers with a height of more than 15 m are protected under category III with an allowable value of R and ≤ 50 Ohm.

For buildings and structures that contain premises requiring lightning protection devices of categories I and II or categories I and III, it is recommended that lightning protection of the facility as a whole be carried out in accordance with the requirements for category I.

Non-explosive premises made of fireproof materials (including partitions, ceilings, roofs) are not equipped with lightning protection devices. The need for lightning protection of granaries, workshops, garages, grain cleaning units is justified taking into account the expected number of lightning strikes into the building. As a rule, the construction of lightning protection at these facilities is not required.

Related information.