MINISTRY OF ENERGY AND ELECTRIFICATION CCC R

MAIN TECHNICAL DEPARTMENT FOR THE OPERATION OF POWER SYSTEMS

GUIDELINES
BY CALCULATION OF PROTECTION ZONES OF ROD AND CABLE
LIGHTNING WIRES

RD 34.21.121

MOSCOW 1974

Compiled by VEI, GNIEI, Energosetproekt

APPROVE:

Deputy Chief

Glavtekhupravleniya

F. SINCHUGOV

GENERAL INFORMATION

The protective effect of lightning rods is based on the fact that lightning is more likely to strike higher and well-grounded metal objects compared to nearby lower ones. A lightning rod, which takes on a lightning discharge, is a metal device towering above the protected structure, consisting of a lightning rod, a down conductor and a ground electrode. To protect electrical installations from direct lightning discharges, it is recommended to use rod and wire lightning rods. Rod lightning rods are made in the form of vertical metal structures installed independently or on any structures (for example, portals, chimneys), and cable lightning rods are in the form of horizontally suspended wires (cables).

The degree of protection of a structure by a lightning rod is determined by the probability of a lightning breakthrough to the protected structure bypassing the lightning rod. The probability of a lightning breakthrough is equal to the ratio of the number of lightning discharges into the protected structure to the total number of lightning discharges into the lightning rod and the protected structure.

Calculation of lightning protection is carried out by protection zones. The probability of a lightning breakthrough to any object located inside the protection zone should not exceed the permissible value.

The outlines and dimensions of the protection zone are determined by the number, height and relative position of the lightning rods and depend on the allowable probability of a lightning breakthrough. The protection zone is the smaller, the lower the probability of a lightning breakthrough is required to be provided. The space between the lightning rods is protected more reliably than on the outside of the lightning rods. The protective effect of lightning rods decreases with an increase in the height of the protected object.

The protection zones of lightning rods up to 60 m high have been tested by many years of operating experience and provide sufficient reliability. The protection zones of lightning rods with a height of more than 60 m according to the methodology of these Guidelines are determined with an estimated probability of a lightning breakthrough into an object no more than 10 -2, and lightning rods - no more than 10 -2 and 10 -3. The estimated probability of a lightning strike is based on laboratory tests on models, operating experience and knowledge of the development of lightning discharges.

PROTECTION ZONES OF LIGHTNING RODS

1. The protection zone of a single rod lightning rod up to 60 m high has the shape shown in fig. , the zone dimensions are determined by the relation

Rice. 1. Protection zone of a single rod lightning rod up to 60 m high:

h- lightning rod height;h x- height of a point on the border of the protected zone;h a = h - h x- active height of the lightning rod

The protection zone of a single rod lightning rod with a heighth60 to 250 m truncated in distance D hfrom the top (Fig. ) and is determined by the relations

Rice. 2. Protection zone of a single rod lightning rod with a height of more than 60 m:

D h = 0,5(h- 60) at 60< h£100m; D h= 0.2 h at h> 100 m

Rice. Fig. 3. Dependence of the height of a single rod lightning rod up to 30 m high on the protection radius at different levelsh x

Rice. 4. Nomogram for calculating the protection zone of a single rod lightning rod up to 30 m high

For protected objects with a height of 60 - 100 m, the height of the lightning rodhdetermined by the nomogram in Fig. , is compared with the critical heighth cr, which defines the truncation boundary of the protection zone,

Rice. 5. Nomogram for calculating the protection zone of a single rod lightning rod up to 100 m high

Due to the truncation of protection zones ath smaller h crthe height of the lightning rod is chosen equal to the critical one.

At the height of lightning rodsh> 100 m, the construction of the protection zone is carried out directly according to the formulas (), () and ().

2. The outlines of the protection zone of two rod lightning rods (double lightning rod) are shown in fig. forh£60m and pic. for £60 h£ 250 m. For each of the lightning rods with a height of more than 60 m, the protection zone is truncated at a distance D hfrom the top, as for a single lightning rod.

Rice. 6. Protection zone of two equally high lightning rods up to 60 m high:

a- distance between lightning rods; in x- the smallest width of the protection zone at the levelh x; r x- radius of the protection zone of a single lightning rod;R- the radius of the circle passing through the tops of the lightning rods and the point 0 , which is at the levelh 0

Rice. 7. Protection zone of two rod lightning rods with a height of more than 60 m:

D h = 0,5(h- 60) at 60< h£100m; D h = 0,2 h at h> 100 m

The construction of the outer zone of lightning rods is carried out similarly to the construction of the zone of a single lightning rod according to the formulas () or () depending on the height. The smallest width of the protection zone in x between lightning rods at the levelh xdetermined from the curves in Fig. and . For lightning rods with a height of 30 to 250 m, the value of both coordinates must be multiplied by the coefficient .

Rice. 8. Values of the smallest width of the protection zone in x two lightning rods with a heighth£30m for

Rice. 9. The value of the smallest width of the protection zone in x two lightning rods for

The smallest height of the protection zoneh 0 for lightning rods up to 30 m high is equal to

(6)

for lightning rods from 30 to 250 m

(7)

but no more h cr, determined by the formula (), ifh³ 60 m.

3. The protection zone of three or more lightning rods significantly exceeds the sum of the protection zones of single lightning rods.

Construction of horizontal sections of the protection zone at the levelh xshown in fig. - on the example of three and four rod lightning rods. Dimensions in x/2 are determined from the curves in fig. and depending ona/ h aand the height of the lightning rod. Protection radiusr xis determined in the same way as for a single lightning rod. With an arbitrary location of several lightning rods, their protection zone can be determined by summing the zones of any three neighboring lightning rods (Fig. ).

Rice. 10. Protection zone of four rod lightning rods of the same height; horizontal section of the protection zone at the levelh x

1, 2, 3, 4 - lightning rods

Rice. 11. Protection zone of three lightning rods of the same height; horizontal section of the protection zone at the levelh x

1, 2, 3 - lightning rods

Rice. 12. Protection zone of four arbitrarily located rod lightning rods of the same height; horizontal section of the protection zone at the levelh x

1, 2, 3, 4 - lightning rods

Part of the protection zone of three or more lightning rods with a height of more than 60 m, located outside the circles passing through the centers of the neighboring three lightning rods, is truncated at a distance D hfrom the top. The part of the zone located inside the circles is not truncated. Value D his determined by the formulas () and ().

A necessary condition for the protection of the entire area at the levelh x is an:

for lightning rods with heighth£30m: D£8 · h a;

for lightning rods height 30< h£250m: D£8 · h a · p,

where D- diameter of a circle drawn through three adjacent lightning rods.

PROTECTION ZONES OF LIGHTNING CABLES

The protection zone of a single wire lightning rod (horizontally suspended wire) has the shape shown in fig. for lightning rods up to 30 m high and in fig. for lightning rods with a height of 30 to 250 m. Protection zone at the levelh xlimited to two lines parallel to the lightning rod, located at a distancer xfrom the vertical plane passing through the lightning rod. This distancer x, conditionally called by analogy with a single rod lightning rod protection radius, are determined by the formulas:

h < 30 м

(8)

for a single wire lightning rod with a heighth from 30 to 250 m

Rice. 13. Protection zone of a single wire lightning rod up to 30 m high:

A- horizontal section of the protection zone at the levelh x; T- rope

Rice. 14. Protection zone of a single wire lightning rod with a height of more than 30 m

Rope lightning rod protection zone height 30< h< 250 м усекается сверху на величину

Rice. 15. Nomogram for calculating the protection zone of a single wire lightning rod up to 30 m high

Rice. 16. Nomogram for calculating the protection zone of a single wire lightning rod with a height of 30 to 100 m

Lightning rod heighth, determined from the nomogram (Fig. ), is compared with the critical height

at h < h crthe height of the lightning rod is chosen equal toh cr. The method for choosing cable protection is based on the dependence of the probability of a lightning breakthrough on the cable protection angle ( a ) and the height of the overhead lines. The correspondence between the technique described here and in the lightning protection section of overhead lines is established by the ratio tg a = r x/ h a.

4. The construction of the protection zone of two parallel wire lightning rods is shown in fig. and . The outer areas of the protection zone are defined as for a single wire lightning rod withh> 30 m and truncated at a distance D hfrom the top. The vertical section of the protection zone between two wire lightning rods is limited by an arc of a circle passing through the lightning rods and the midpoint between the lightning rodsOat the height

(11)

where a - distance between lightning rods;

Rice. 17. Protection zone of two wire lightning rods 1 and 2 up to 30 m high:

I - horizontal section at the levelh x; II - vertical section of the protection zone

Rice. 18. Protection zone of two wire lightning rods with a height of more than 30 m

R= 1 at h£30m; nineteen . Around lightning rod 1 of greater height, a protection zone is built, as for a single lightning rod. Further, a horizontal line is drawn through the top of the lightning rod 2 of a lower height until it intersects with the protection zone of the lightning rod 1. Taking this intersection point as the top of some fictitious lightning rod 3 of the same height as the smaller lightning rod, a protection zone is built for two lightning rods 2 and 3, the outlines of which limit the inner section of the total protection zone.

Rice. 19. Protection zone of two lightning rods of different heights:

1, 2 - lightning rods; 3 - top of fictitious lightning rod

For lightning rods with heighth> 60 m and rope h> 30 m, the protection zone at their top is truncated at a distance D hfrom the top specifically for each of the lightning rods and in accordance with their type.

The total protection zone of cable and rod lightning rods is determined by the overlap of their zones. The configuration of the protection zone at the end of the wire lightning rod is also built. In this case, the end of the cable should be considered as a lightning rod of the appropriate height.

Protection zones with a breakthrough probability of no more than 10 -2 are intended for open switchgears of stations and substations, as well as for utility structures that need lightning protection. In this case, the inputs of devices and busbars should be located as far as possible in the depth of the protection zone, since their defeat by lightning represents the greatest danger.

Protection zones with a breakthrough probability of no more than 10 -3 are intended for high-critical busbar trunking sections, which, due to their high height or length, may be subject to frequent lightning strikes.

The reliability of protection is increased by placing objects in the inner part of the protection zone of multiple lightning rods.

Due to the probabilistic nature of lightning breakthroughs, the implementation of lightning protection, which completely excludes the defeat of protected objects, is not always expedient, and in some cases it is not technically feasible. The optimal reliability of lightning protection is determined on the basis of a comparison of the cost of lightning protection and the possible damage from a lightning strike.

The reliability of lightning protection is characterized by the number b lightning strikes per year per protected structure or the number of years in which one lightning breakthrough into the protected area is expected

b = ψ N,

where ψ - the probability of a breakthrough into the protection zone (10 -2 or 10 -3, respectively, to the zone);

N- the total number of strikes per year to the lightning rod and the protected structure.

Expected number of lightning strikes and year into a single towering structure (including a lightning rod) with a heighth meters:

N = n Tπ R 2 10 -6 , (12)

where n\u003d 0.06 - the number of lightning strikes into the ground with an area of \u200b\u200b1 km 2 per 1 hour of a thunderstorm, ;

T- the average intensity of thunderstorm activity for a given area, h.

R= 3.5 h- the equivalent radius of the circle describing the area from which the structure "collects" lightning, m.

The number of lightning strikes per year in a group of towering structures (including a group of lightning rods):

T = nts 10 -6 , (13)

where S- the area bounded by arcs of circles described by a radiusRaround each lightning rod, m 2 .

The number of strikes per year into an extended towering structure (including a lightning rod) with a heighth and length l ,(m):

N= 2 nTLR 10 -6 , (14)

where R = 3,5 h.

Number of strokes per structure lengthl(m), width m(m) and height h(m) is determined by the formula (), where

S=(l + 7 h)(m + 7 h). (15)

LIGHTNING WIRE - a device for protecting buildings and structures from direct lightning strikes. M. includes four main parts: a lightning rod that directly perceives a lightning strike; down conductor connecting the lightning rod with the ground electrode; ground electrode through which the lightning current flows to the ground; the bearing part (support or supports) intended for fixing the lightning rod and down conductor.

Depending on the design of the lightning rod, rod, cable, mesh and combined lightning rods are distinguished.

According to the number of jointly acting lightning rods, they are divided into single, double and multiple.

In addition, at the location of M. there are separate, isolated and not isolated from the protected building. The protective action of lightning is based on the property of lightning to strike the highest and well-grounded metal structures. Due to this property, a protected building that is lower in height is practically not struck by lightning if it enters the M protection zone. The M protection zone is the part of the space adjacent to it and with a sufficient degree of reliability (at least 95%) providing protection for structures from direct strikes lightning. Most often, rod M is used to protect buildings and structures.

Rope lightning is most often used to protect buildings of great length and high-voltage lines. These M. are made in the form of horizontal cables fixed on supports, along each of which a current collector is laid. Rod and cable M. provide the same degree of reliability of protection.

As lightning rods, you can use a metal roof, grounded at the corners and along the perimeter at least every 25 m, or a steel wire mesh with a diameter of at least 6 mm superimposed on a non-metal roof, having a mesh area of up to 150 mm2, with knots fixed by welding, and grounded just like a metal roof. Metal caps are attached to the grid or conductive roof above the chimneys and ventilation pipes, and in the absence of caps, wire rings specially applied to the pipes.

M. rod - M. with a vertical arrangement of the lightning rod.

M. cable (extended) - M. with a horizontal arrangement of the lightning rod, fixed on two grounded supports.

LIGHTNING PROTECTION ZONES

Usually, the zone of protection is designated by the maximum probability of a breakthrough corresponding to its outer border, although the probability of a breakthrough decreases significantly in the depth of the zone.

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

In terms of reliability theory, the breakthrough probability is a parameter that characterizes the failure of a lightning rod as a protective device. With this approach, the two accepted protection zones correspond to the degree of reliability of 0.9 and 0.99. This reliability assessment is valid when an 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 in the depth of the zone. The assessment of the reliability of the protection zone along its outer border leads to excessively low values. Therefore, in order to take into account the mutual arrangement of lightning rods and objects existing 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.

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 h0

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

Zone A: h0 = 0.85h,

r0 = (1.1 - 0.002h)h,

rx = (1.1 - 0.002h)(h - hx/0.85).

Zone B: h0 = 0.92h;

rx \u003d 1.5 (h - hx / 0.92).

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

h = (rx + 1.63hx)/1.5.

Rice. P3.1. Protection zone of a single rod lightning rod:

I - the boundary of the protection zone at the hx level, 2 - the same at ground level

Single wire lightning rod.

The protection zone of a single wire lightning rod with a height h? 150 m is shown in fig. P3.5, where h is the height of the cable in the middle of the span. Taking into account the sag of the cable with a cross section of 35-50 mm2, with a known height of supports hop and span length a, the height of the cable (in meters) is determined:

h = hop - 2 at a< 120 м;

h = hop - 3 at 120< а < 15Ом.

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

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

For a zone of type B, the height of a single wire lightning rod with known values of hx and rx is determined by the formula

The vertical ground electrode is made by successive mechanized immersion of threaded electrodes 1.2-3 meters long, interconnected by brass couplings. Steel electrodes with a diameter of 14.2-17.2 mm, with an electrochemical copper coating (99.9% purity), 0.25 mm thick. guarantees high corrosion resistance and service life of the earth electrode in the ground for at least 40 years. The high mechanical strength of the earth electrode allows it to be immersed to a depth of up to 30 meters. The copper coating of the electrodes has high adhesion and plasticity, which makes it possible to immerse the rods in the ground without breaking the integrity and peeling off the copper layer.

Depending on the design of the lightning rod, rod, cable, mesh and combined lightning rods are distinguished.

According to the number of jointly acting lightning rods, they are divided into single, double and multiple.

M. rod - M. with a vertical arrangement of the lightning rod.

M. cable (extended) - M. with a horizontal arrangement of the lightning rod, fixed on two grounded supports.

LIGHTNING PROTECTION ZONES

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 h0

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

Zone A: h0 = 0.85h,

r0 = (1.1 - 0.002h)h,

rx = (1.1 - 0.002h)(h - hx/0.85).

Zone B: h0 = 0.92h;

rx \u003d 1.5 (h - hx / 0.92).

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

h = (rx + 1.63hx)/1.5.

Rice. P3.1. Protection zone of a single rod lightning rod:

I - the boundary of the protection zone at the hx level, 2 - the same at ground level

Single wire lightning rod.

h = hop - 2 at a< 120 м;

h = hop - 3 at 120< а < 15Ом.

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

INTRODUCTION

Distribution electrical networks (PC) with a voltage of 0.4-10 kV in recent years are equipped with electrical equipment, devices, devices, insulators and wires, made on a new modern technical base. The operation of such network facilities requires a reliable lightning surge protection system using modern technical means. The development of technical means and methods of protection against surges PC is associated with a quantitative assessment of the parameters of lightning and the probable number of lightning damage. To calculate the density of direct lightning strikes on the ground, information on the intensity of thunderstorm activity is used. In this case, it is necessary to take into account the shielding of network objects by buildings, structures, trees, etc. Shielding in some cases can reduce the number of direct hits to network objects by ~ 70%.

Reliable protection is achieved if the equipment and structures have a sufficiently high insulation strength or effective lightning surge protection devices are installed in the PC. To protect PCs with a voltage of 0.4-10 kV from lightning surges, non-linear surge arresters (OPN), long-spark arresters (RDI), valve arresters (RV) and tubular arresters (RT), protective spark gaps (IP) are used. The type, number and installation location of protection devices is selected when designing specific network facilities. When installing protection devices, the requirements for the value of ground resistance are selected according to the PUE. For main lines with a voltage of 6-10 kV, made in the dimensions of an overhead line with a voltage of 35 kV, it is recommended to use wire lightning rods at the approaches to substations and distribution points.

The task of protecting the PC with a voltage of 0.4 kV is to prevent damage to people, animals and the occurrence of fires due to the penetration of lightning surges into the internal wiring of residential buildings and other buildings, as well as damage to the electrical equipment of 6-10 / 0.4 kV substations.

EVALUATION OF THE PROTECTIVE ACTIVITY OF LIGHTNING WIRES

Parameters of rod and wire lightning rods

Parameters of rod lightning rods

A rod lightning rod is a structure in the form of a vertically installed lattice spire, pipe or rod. A rod lightning rod as a means of lightning protection was proposed by W. Franklin in 1749. Modern lightning rods of standard types have a height of up to 40 meters. In some cases, to create non-standard lightning rods, factory pipes, power line supports or metal portals of open switchgear are used as load-bearing structures.

The lightning rod must have a reliable connection with the ground with a resistance of 5-25 ohms to the spreading of the impulse current. The protective property of rod lightning rods is that they orient the leader of the emerging lightning discharge towards themselves. The discharge occurs necessarily at the top of the lightning rod, if it is formed in a certain area located above the lightning rod. This area has the form of an upward expanding cone and is called the 100% lesion zone. It has been established by experimental data that the lightning orientation height H depends on the height of the lightning rod h. For lightning rods up to 30 meters high:

and for lightning rods with a height of more than 30 meters H=600m, it is considered that the top of the cone of the zone of 100% damage is located symmetrically to the axis of the lightning rod at the height of the protected object, and its radius is at the orientation height:

where is the active part of the lightning rod, corresponding to its excess over the height of the protected object:

In addition to the specified zone, the protective effect of a rod lightning rod is characterized by a protection zone, i.e. space where lightning strikes are excluded. The protection zone of a single rod lightning rod has the form of a tent, expanding downwards (Fig. 1.1). To calculate the protection radius at any point of the protective zone, including at the height of the protected object, the following formula is used:

where p is a correction factor equal to 1 for lightning rods with a height of less than 30 meters and equal to higher lightning rods.

In the case when several lightning rods are used to protect extended objects, it is advisable that the zones of their 100% defeat close over the object or even overlap each other, excluding a vertical lightning breakthrough to the protected object (Fig. 1.2). The distance (S) between the axes of the lightning rods must be equal to or less than the value determined from the dependence:

The protection zone of two and four rod lightning rods in the plan at the level of the height of the protected object has the outlines shown in Fig. 1.3, a, b.

The protection radius shown in the figure is determined in the same way as for a single lightning rod, and the smallest width of the protection zone is determined by special curves. It should be borne in mind that with lightning rods up to 30 meters high, located at a distance, the smallest width of the protection zone is equal to zero.

Figure 1.1 - Protection zone of a single rod lightning rod:

1 - the border of the protection zone; 2 - section of the protection zone at the level

Figure 1.2 - Scheme of the arrangement of rod lightning rods, ensuring the closing of zones of 100% damage

Figure 1.3 - Graphical representation of the protective zone:

a) - for two lightning rods; b) - for four lightning rods

In the presence of three and four lightning rods, the outlines of the protective zone look like Fig. 1.3 b. The protection radii are determined in this case in the same way as for single lightning rods. The size is determined from the curves for each pair of lightning rods. The diagonal of a quadrilateral or the diameter of a circle passing through the vertices of a triangle formed by three lightning rods, according to the conditions of protection of the entire area, must satisfy the dependencies for lightning rods with a height of less than 30 m:

for lightning rods with a height of more than 30 m:

When installing free-standing lightning rods, it is necessary to observe certain air distances between the lightning rod and the protected object. This requirement comes from the fact that at the moment of a lightning strike of a lightning rod, a high potential is created on it, which can lead to a reverse discharge from the lightning rod to the object. The potential at the lightning rod at the moment of discharge is determined by the dependence:

where - impulse grounding resistance of the lightning rod 5 - 25 Ohm; - lightning current in a well-grounded object, kA.

More precisely, the potential at the lightning rod can be determined taking into account the inductance

lightning rod activity:

where a is the steepness of the current wave front, kA/μs; - lightning rod point at the height of the object, m; - specific inductance of the lightning rod, μH/m.

To calculate the minimum allowable approach of an object to a lightning rod, one can proceed from the dependence:

where E in is the permissible impulse electric field strength in the air, assumed to be 500 kV / m.

Guidelines for surge protection recommend that the distance to the lightning rod be taken equal to:

This dependence is valid for a lightning current of 150 kA, a current slope of 32 kA/μs and a lightning rod inductance of 1.5 μH/m. Regardless of the results of the calculation, the distance between the object and the lightning rod must be at least 5 m.

Rope lightning rod

One of the most reliable means of preventing direct lightning strikes of power transmission lines is the suspension of grounded wire lightning rods above them. This device is expensive and therefore is used only on first-class lines with a voltage of 110 kV and above. When the line on metal or wooden supports is not completely covered with cables, they cover only approaches to substations in a section of 1-2 km. Depending on the design of the supports, one or two cables can be used, tightly attached to the metal support or to the grounding metal slopes of the wooden supports. To protect the cable from overburning by lightning current and to control grounding, the support of the cable is made using one suspension insulator shunted with a spark gap. The efficiency of cable protection is the higher, the smaller the angle formed by the vertical passing through the cable and the line connecting the cable with the outermost of the wires. This angle is called the protective angle, taking its value in the range of 20-30 0 .

The protective zone for one cable in the cross section perpendicular to the line has the form similar to the protective zone for a single rod lightning rod. The width of the protective zone, which excludes direct damage to the wires at the level of their suspension height, is determined by the dependence:

This dependence is valid for a cable suspension height of 30 m and below.

The protective effect of a lightning rod is based on the fact that lightning is more likely to strike taller and well-grounded objects, compared to nearby objects of lower height. Therefore, the lightning rod, which rises 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 strikes to the protected object (the number of breakthroughs) to the total number of strikes to the lightning rod and the object.

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

Approach to standardization of lightning protection ground electrodes

One of the effective ways to limit lightning surges in the lightning rod circuit, as well as on the metal structures and equipment of the facility, is to ensure low resistance of grounding conductors. Therefore, when choosing lightning protection, the resistance of the ground electrode or its other characteristics associated with the resistance is subject to rationing.

For outdoor installations, the maximum allowable impulse resistance of ground electrodes was assumed to be 50 ohms.

At present, reinforced concrete foundations are common and recommended designs of grounding conductors. They are subject to an additional requirement - the exclusion of mechanical destruction of concrete during the spreading of lightning currents through the foundation. Reinforced concrete structures withstand high densities of lightning currents spreading through 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 footboards with a length of at least 2 m) are capable of withstanding lightning currents up to 100 kA without destruction. For large foundations with a correspondingly larger reinforcement surface, a current density dangerous for concrete destruction is unlikely for any possible lightning currents.

Rationing the parameters of ground electrodes according to their typical designs has a number of advantages: it corresponds to the unification of reinforced concrete foundations accepted in construction practice, taking into account their widespread use as natural ground electrodes; when choosing lightning protection, it is not required to perform calculations of impulse resistances of grounding conductors, which reduces the amount of design work.

General provisions for lightning protection device

Lightning protection devices (lightning rods) should include lightning rods that directly perceive a lightning strike, down conductors and ground electrodes.

Rod lightning rods must be made of steel (round, strip, angle, tubular) of any grade with a cross section of at least 200 mm 2, a length of at least 500 mm and mounted on a support or directly on the protected building or structure itself.

Rope lightning rods must be made of steel multiwire ropes with a cross section of at least 50 mm 2.

Down conductors connecting lightning rods of all types with grounding conductors should be made of steel. Their dimensions must be at least as follows:

Outdoor building Outdoor Ground

Diameter of round down conductors and jumpers, mm 8 -

Diameter of round vertical (horizontal) electrodes, mm - 16(14)

Section (thickness) of rectangular down conductors, mm 2 (mm) 50(4) 160(4)

The lightning protection mesh must be made of galvanized steel conductors with a diameter of at least 8 mm, laid on the non-metallic roof of the building on top or under fireproof or hardly combustible insulation or waterproofing. The size of the grid cells should be no more than 6x6 m. The grid at the nodes should be connected by welding.

In buildings with coatings on metal trusses or beams, lightning protection mesh is not laid on the roof. In this case, the supporting structures of the coating must be connected with down conductors made of A1 steel rods with a diameter of 12 mm. All metal parts located on the roof (pipes, ventilation devices, drain funnels, etc.) must be connected to the lightning protection mesh with lightning rods. On non-metallic elevated parts of buildings, an additional metal mesh should be laid and connected by welding to the lightning protection mesh on the roof.

When laying a lightning protection mesh and installing lightning rods, 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 on the protected object wherever possible, provided that continuous electrical connection in the joints of structures and fittings with lightning rods and grounding conductors, performed, as a rule, by welding

It is allowed to use all ground electrodes of electrical installations recommended by the PUE, with the exception of neutral wires of overhead power lines with voltage up to 1 kV, as lightning protection ground electrodes.

Reinforced concrete foundations of buildings, structures, outdoor installations, supports of lightning rods should, as a rule, be used as lightning protection grounding conductors, provided that a continuous electrical connection is provided through their reinforcement and its connection to embedded parts by welding.

Bituminous and bitumen-latex coatings are not an obstacle to such use of foundations. In medium and highly aggressive soils, where reinforced concrete is protected from corrosion by epoxy and other polymer coatings, as well as when soil moisture is less than 3%, it is not allowed to use foundations as ground electrodes.

Artificial grounding should be placed 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.).

Equalization of potentials inside buildings and structures with a width of more than 100 m should occur due to a continuous electrical connection between the load-bearing intra-shop structures and reinforced concrete foundations, if the latter can be used as ground electrodes. Otherwise, laying inside the building in the ground at a depth of at least 0.5 m of extended horizontal electrodes with a cross section of at least 100 mm 2 should be provided. Electrodes should be laid at least 60 m across the width of the building and connected at its ends on both sides to the external ground loop.

In frequently visited open areas with an increased risk of lightning strikes (near monuments, TV towers and similar structures more than 100 m high), potential equalization is carried out by connecting the current conductors or fittings of the structure to its reinforced concrete foundation at least 25 m along the perimeter of the base of the structure.

If it is impossible to use reinforced concrete foundations as ground electrodes 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 mm 2 and a length of 2-3 m should be laid, connected to the ground electrodes protecting the structure from direct lightning strikes.

During the construction of high buildings and structures on them during the thunderstorm period, starting from a height of 20 m, it is necessary to provide for the following temporary lightning protection measures. Lightning rods should be fixed at the upper mark of the object under construction, which should be connected through metal structures or down conductors freely descending along the walls to the grounding conductors specified in paragraphs. 3.7 and 3.8 RD. The type B protection zone of lightning rods should include all outdoor areas where people can be during construction. Connections of lightning protection elements can be welded or bolted. As the height of the object under construction increases, lightning rods should be moved higher.

Devices and measures for lightning protection that meet the requirements of these standards must be included in the project and schedule for the construction or reconstruction of the building in such a way that the implementation of lightning protection occurs simultaneously with the main construction and installation works.

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

At the same time, the corrected design documentation for the lightning protection device (drawings and explanatory note) and acts of acceptance of lightning protection devices, including acts for covert 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 the frame of the building as down conductors and lightning rods, as well as the results of measurements of the resistance to the current of industrial frequency of grounding conductors of separate lightning rods.

Checking the condition of lightning protection devices should be carried out 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 1 time in 3 years.

The integrity and protection against corrosion of the visible parts of lightning rods and down conductors and the contacts between them, as well as the value of the resistance to current of the industrial frequency of grounding conductors of separate lightning rods, are subject to verification. This value should not exceed the results of the corresponding measurements at the acceptance stage by more than 5 times. Otherwise, the grounding conductor should be revised.

Depending on the specific conditions, various options (or combinations thereof) of lightning protection are possible. The easiest way is to equip a house with a metal roof with a lightning protection system. To do this, it is enough to bring a down conductor to two opposite roof slopes and connect them to grounding conductors (for example, a water pipe). Drainpipes can be used as down conductors, grounding them, if necessary, using a vertical or horizontal ground electrode.

A structure with a non-metal roof can be equipped with a cable lightning protection system in the form of a steel wire stretched along the ridge of the roof with a diameter of 5-6 mm with lightning rods located above the highest point of the structure or its elements. A wire with a gap of 250 mm from the roof ridge is pulled between wooden posts mounted on gables, if it is located above other building elements (for example, a chimney), then in this case it can be considered a lightning rod.

Cable lightning protection system:

a - general view; b - fastening the "fork" on the pipe; c - the correct location of the wire lightning rod; 1 - rod lightning rod; 2 - cable lightning rod; 3 - racks;

4 - blind area; 5 - ground electrode; 6 - humidification zone; 7 - footpath; 8 - down conductor