Below explains the approach to the definition of lightning protection zones, the construction of which is carried out by formulas appendices 3. RD 34.21.122-87.

The protective effect of the lightning conduction is based on the "zipper property with a greater probability to affect higher and well-grounded items compared to sitting near the objects of a smaller height. Therefore, by a lightning resulting, towering over the protected object, the function of interception of lightning, which in the absence of a lightning conduction would be struck by the object. Quantitatively The protective effect of the lightning conduction is determined through the probability of a breakthrough - the ratio of the number of lightning strikes into a protected object (number of breakthroughs) to a total number of shocks in a lightning conductor and an object.

There are several ways to assess the probability of breakthrough based on different physical ideas about the processes of damage to lightning. In the RD 34.21.122-87, the results of calculations on a probabilistic procedure that binds the likelihood of lesion of the lightning conduction and an object with a scattering of downlink trajectories without taking into account its current variations is used.

According to the adopted settlement model, it is impossible to create perfect protection against direct lightning strikes, fully eliminating breakthroughs on the protected object. However, in practice, the mutual arrangement of the object and the lightning conduction, which provides a low probability of a breakthrough, for example, 0.1 and 0.01, which corresponds to a decrease in the number of lesions of the object by about 10 and 100 times compared to the object where there is no lightning discharge. For most modern objects, at such levels of protection, a small number of breakthroughs for the entire service life is ensured.

The above was considered a production building with a height of 20 m and dimensions in terms of 100 × 100 m, located in the area with a duration of the thunderstorm 40-60 hours per year; If this building is protected by lightning lines with a breakthrough chance of 0.1, it can be expected not more than one breakthrough for 50 years. At the same time, not all breakthroughs are equally dangerous for the protected object, such as ignitions are possible at high currents or portable charges, which are not found in each lightning discharge. Therefore, one dangerous impact on this object can be expected per longer than 50 years old or for most industrial facilities II and III categories of no more than one dangerous impact for their existence. If you probably have a breakthrough of 0.01 at the same building, you can expect no more than one breakthrough for 500 years - a period much more than the service life of any industrial facility. Such a high level of protection is justified only for category I objects representing a constant threat of an explosion.

By performing a series of calculation of the probability of a breakthrough in the vicinity of the lightning conduction, one can construct a surface that is a geometric position of the position of the vertices of protected objects, for which the probability of a breakthrough is a constant value. This surface is the outermost boundary of the space, called the zone-sized protection zone; For a single stripping hill, this border is a side surface of a circular cone, for a single cable - a double flat surface.

Usually, the protection zone is denoted by the maximum probability of a breakthrough corresponding to its outer boundary, although in the depth of the zone, the probability of a breakthrough is significantly reduced.

The estimated method allows us to be constructed for rod and cable lightning systems of protection with an arbitrary probability of a breakthrough, i.e. For any lightning room (single or double), you can build an arbitrary number of protection zones. However, for most national economic 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 conductor as a protective device. With this approach, two adopted protection zones corresponds to the degree of reliability of 0.9 and 0.99. Such an assessment of the reliability is valid when the object is located near the boundaries of the protection zone, such as an object in the form of a ring, coaxial with a rod lightning conductor. In the 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. Assessing the reliability of the protection zone at its external border leads to excessively low values. Therefore, to take into account the interconnection of lightning and objects in practice, the protection zones A and B is attributed to the RD 34.21.122-87 the estimated degree of reliability of 0.995 and 0.95, respectively.

Fig. 1. Nomograms for determining the height of single (A) and double equal height (b) lightning-lines in the zone A

The estimated probability of the breakthrough is designed only for descending lightning, preferably affecting objects height up to 150 m. Therefore, in the RD 34.21.122 - 87, the formulas for constructing the protection zones of single and multiple rod and cable lightning systems are limited to a height of 150 m. To date, the amount of actual data The lesibility of the descending lightning objects of greater height is very small and mainly refers to the Ostankino television tower (540 m). Based on the photoporegistrations, it can be argued that descending lightning breaks through more than 200 m below its vertex and affect the land at a distance of about 200 meters from the base of the tower. If we consider the Ostankino television tower as a rod lightning conduction, it can be concluded that the relative dimensions of the lightning stroke areas with a height of more than 150 m are rarely reduced with increasing lightning height. Taking into account the limitedness of the actual data on the impact of ultra-high objects in the RD 34.21.122 - 87, formulas for constructing protection zones only for rod lightning lines with a height of more than 150 m.

Fig. 2. Nomograms for determining the height of single (a) and double equal height (b) lightning-discovers in the zone b

The method of calculating the protection zones from lesions by ascending lightning has not yet been developed. However, according to observations, it is known that the upstream discharges are excited from pointed items near the tops of high structures and make it difficult to develop other discharges with lower levels. Therefore, for such high objects, both reinforced concrete pipes or towers are provided, first of all, protection against mechanical destruction of concrete when the ascending lightning is excited, which is carried out by installing rod or ring lightningness, providing the maximum possible constructive considerations over the top of the object ( p. 2.31).

This manual contains nomograms to determine the heights of the rod FROM and trails T. Single and double lightning systems providing protection zones A and B (Fig. 1 and 2). The use of these nomograms built in accordance with the calculated formulas and notation appendices 3. RD 34.21.122-87 allows you to reduce the amount of calculations and simplify the choice of means of lightning protection during design.

Lightning game directly perceives the straight blow of the zipper. Therefore, it should reliably confront the mechanical and thermal effects of the current and high-temperature zipper channel. The carrying design bears on itself lightningness and a cocoquer, combines all elements of the lightning loss in a single, rigid, mechanically durable design. In electrical installations, lightning tracks are installed near the current-carrying parts under the operating voltage. The drop in the lightning conduction on the current-host elements of the electrical installation causes a heavy accident. Therefore, the bearing design of the lightning conductor should have a high mechanical strength, which would eliminate the incidence of falling the lightning conduction to the equipment of power plants and substations. Lightning conductor should have a reliable connection with the earth with a resistance of 5-25 ohms of a pulse current. The protective property of rod lightning lines is that they focus on the leader of the emerging thunderstorm discharge. The discharge occurs necessarily at the vertex of the lightning conduction, if it is formed in some region located above the lightning conductor. This area has the form of an expanding up cone and is called a zone of 100% lesion.

The experimental data found that the height of the orientation orientation H depends on the height of the lightning conduction H. For lightning lighters high up to 30 meters:

and for lightning lines height more than 30 meters H \u003d 600 m.

where is the active part of the lightning conduction corresponding to its exceeding over the height of the object being protected:

Figure 1.1 area of \u200b\u200bprotection of a single rod lightning conductor: 1 - the boundary of the protection zone; 2 - Section of the protection zone at the level.

To calculate the protection radius at any point of the protective zone, including at the level of the height of the protected object, the formula is used:

where is a correction factor equal to 1 for lightning lighters height less than 30 meters and equal to higher lightning systems.

The zones of the protection of extended objects in which several lightning sides are used, it is advisable that the zones of their 100% lesions are closed over the object or even overlap each other, excluding the vertical breakthrough of the lightning on the protection object (S) between the lightning axes should be equal to or less than the magnitude, determined from the dependence:

The protection zone of two and four rod lightning systems in terms of the height of the protected object has the outlines shown in Figure 1.3, and, b.

The smallest width of the protection zone shown in the drawing radius of protection is defined in the same way as for a single lightning conduction, but is determined by special curves. Figure 1.2 shows the design of rod lightning lines. If the lightning lifters have a height of up to 30 meters located at a distance, the smallest width of the protection zone is zero.

Figure 1.2 of the design of rod lightning systems on reinforced concrete supports: A - with vibrated concrete; B - Centrifugated concrete

Figure 1.3 Rod lightning rods on metal supports: A - Cable lightning (carrying construction); B - rod lightning-conducting (carrying construction)

Figure 1.3 shows the design of rod lightning lines on metal supports. Protection radii are determined in this case as well as for single lightning lighters. The size is determined by curves for each pair of lightning. The diagonal of the quadrilateral or the diameter of the circle passing through the vertices of the triangle formed by three lightning lines, under the conditions of the entire area, the dependence must satisfy the dependencies:

For lightning lighters height less than 30 m:

For lightning lighters with a height of more than 30 m:

Separately standing rod lightningways with metal supports are mounted on reinforced concrete foundations. Toko-separated for such lightning systems serve supporting structures. On the metal and reinforced concrete structures of the engine, lightning tracks with metal carriers are installed. The design of their fastening is determined by the characteristics of the design of the yeast, to which the rod lightning conduction is mounted. Typically, the design of the lightning sequers installed on the structures of the engine is a steel pipe that is often consisting of multiple diameters. Lightning lines with a height of more than 5 m at the base have a lattice design of angular steel. The potential at the lightning conduction at the time of the discharge is determined by the dependence:

where - the pulse resistance of grounding of a lightning conduction 5-25 ohms;

Lightning current in a well-grounded object.

The potential at the lightning conductor is determined:

where - the steepness of the current wave front;

• - point of the lightning lifting at the height of the object;
• - Specific inductance of a lightning conductor.

To calculate the minimum allowable approximation of the object to the lightning loss, it can be processed from the dependence:

where - the permissible pulse voltage of the electric field in the air received by 500 kV / m.

Overvoltage Protection Guidelines Recommend the distance to a lightning conduction to take equal:

This dependence is valid at a lightning current equal to 150 ka, 2 ka / mxkek current and lightning inductance 1.5 μg / m. Regardless of the results of the calculation, the distance between the object and the lightning resulting should be at least 6 meters.

Cable lightning. The values \u200b\u200bof the coefficients K and Z are taken depending on the probability of a breakthrough of lightning into the protection zone. The probability of lightning breakthrough into the protection zone is equal to the ratio of the number of lightning discharges into the protected structure to the total number of lightning discharges in a lightning conduction and the protected structure. If the likelihood of a breakthrough in a zone of protection 0.01 is allowed, then the coefficient 1, and with a probability of 0.001, i.e., protective zones of cable lightning systems are somewhat less protective zero-lighting zones. The form of the protection zone of two parallel cable lightning systems with a height of up to 30 m. The external boundaries of the protection zone of each cable are defined in the same way as for a single cable lightning conduction. Depending on the design of the supports, one or two cables can be applied, tightly attached to the metal support or to ground metal descents of wooden supports. To protect the cable from the stroke of zipper and control the grounding, the support of the cable fastening is made with a single suspension insulator, the spark interval. The effectiveness of the cable protection is higher, the less angle formed by the vertical passing through the cable, and the line connecting the cable with the extreme of wires. This angle is called a protective angle, taking its magnitude within

The protection zone of two cable lightning lighters with a height of more than 30 m. The method of constructing the protection zone for this case is the same as for cable lightning rods up to 30 m high, but at a distance from the top of the zone fears the same as single cable lightning. The width of the protective zone that excludes the direct damage of the wires at the level of the height of their suspension is determined by the dependence:

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

Ministry of Energy and ElectrificationCCC R.

Main technical managing power management power system

GUIDELINES
By calculating the zerry and cable protection zones
Lightning Songs

RD 34.21.121

Moscow 1974.

Compiled by WEI, GNIEI, power project

I argue:

Deputy Head.

Headtejeplation

F. Sinchugov

General

The protective effect of lightning lines is based on a zipper property with a greater probability to affect higher and well grounded metal objects compared to nearby less than high. Lightning resulting, which takes on a lightning discharge, is a metal device consisting of lightning parameters, a toxic and earthing on the protected structure. To protect electrical installations from direct lightning discharges, it is recommended to use rod and cable lightning rods. Rod lightning rods are performed in the form of vertical metal structures installed on their own or on any structures (for example, portals, flue pipes), and cable - as horizontally suspended wires (cables).

The degree of protection of the construction of a lightning conductor is determined by the likelihood of a breakthrough of lightning to a protected structure bypassing the lightning result. The probability of lightning breakthrough is equal to the ratio of the number of lightning discharges into a protected structure to a total number of lightning discharges in a lightning conduction and a protected structure.

Calculation of lightning protection is carried out on protection zones. The likelihood of a breakthrough of lightning 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 mutual position of the lightning lines and depend on the allowable probability of the lightning breakthrough. The protection zone is the less, the smaller the likelihood of a lightning breakthrough is required to ensure. The space between the lightning lifts is protected more reliable than from the outside of lightning. The protective effect of lightning lines is reduced with an increase in the height of the protected object.

The zones of protection of rod lightning systems up to 60 m tested by many years of experience and provide sufficient reliability. The zones of protection of rod lightning lighters with a height of more than 60 m according to the method of these guidelines are determined with the estimated probability of a breakthrough of the lightning into the object not more than 10 -2, and the cable lightning systems are not more than 10 -2 and 10 -3. This estimated probability of lightning breakthrough is established on the basis of laboratory tests on the model, experience and information about the development of lightning discharges.

Ride Lighting Zones

1. The zone of protection of a single rod lightning conductor height up to 60 m has the shape shown in Fig. , zone dimensions are determined by the ratio

Fig. 1. The protection zone of a single rod lightning conductor with a height of up to 60 m:

h. - lightning height;h X. - the height of the point at the boundary of the protected zone;h a \u003d h - h x - active lightning height

Single Rod Lighting Height Protection Areah. from 60 to 250 m is truncated at a distanceD. h. from the vertex (Fig.) and is determined by the ratios

Fig. 2. The zone of protection of a single rod lightning conductor with a height of more than 60 m:

D. h. = 0,5(h. - 60) at 60< h.£ 100 m; D. h. \u003d 0.2 · h. for h. \u003e 100 meters

Fig. 3. The dependence of the height of a single rod lightning conductor with a height of up to 30 m from the protection radius at various levelsh X.

Fig. 4. Nomogram for calculating the zone of protecting a single rod lightning conductor height up to 30 m

For protected objects with a height of 60 - 100 m height of the lightning conductionh.defined by nomogram Fig. compared with critical heighth krdetermining the truncation boundary of the protection zone,

Fig. 5. nomogram for calculating the zone of protection of a single rod lightning conduction height up to 100 m

Due to the truncation of protection zonesh. less h kr Lightning height is chosen equal to critical.

With lightning heightsh. \u003e 100 m Construction of the protection zone is made directly by formulas (), () and ().

2. The outlines of the protection zone of two rod lightning systems (double lightning conduction) are shown in Fig. forh.£ 60 m and rice. for 60 £. h.£ 250 m. For each of the lightning systems, a height of more than 60 m, the protection zone is truncated at a distanceD. h. From the top, as well as for a single lightning conductor.

Fig. 6. The protection zone of two equivalent stem lightning lines with a height of up to 60 m:

but - distance between lightning lifts; in X. - the smallest width of the protection zone at the levelh X.; r X. - radius of the protection zone of a single lightning conduction;R. - Radius of the circle passing through the vertices of lightning lines and the point 0 attendedh 0.

Fig. 7. The protection zone of two rod lightning lines with a height of more than 60 m:

D. h. = 0,5(h. - 60) at 60< h.£ 100 m; D. h. = 0,2 h. for h. \u003e 100 meters

The construction of the outer zone of lightning systems is made similar to the construction of the zone of a single lightning conduction by formulas () or () depending on the height. The smallest width of the protection zone in H. between lightning lines at the levelh X. Determined by curve Fig. and. For lightning lighters height from 30 to 250 m, the value of both coordinates must be multiplied by the coefficient.

Fig. 8. The value of the smallest width of the protection zone in H. two rod lightning lighters highh.£ 30 m for

Fig. 9. The value of the smallest width of the protection zone in H. two rod lightning lines for

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

(6)

for lightning lines from 30 to 250 m

(7)

but no more h krdefined by the formula () ifh.³ 60 m.

3. The protection zone of three and more lightning consists significantly exceeds the amount of the zones of protection of single lightning systems.

Building horizontal sections of the protection area at the levelh X. Showing in Fig. - On the example of three and four sodium lightning. Dimensions in H./ 2 are determined by curve fig. and depending ona./ h A. And the height of the lightning room. Radius protectionr X. Determined in the same way as for a single lightning conduction. With an arbitrary arrangement of several lightning systems, their protection zone can be determined by the summation of the zones of any three adjacent lightning systems (Fig.).

Fig. 10. The protection zone of four sodium lightning lines of the same height; Horizontal sectional protection area at levelh X.

1, 2, 3, 4 - Lightning conductors

Fig. 11. The protection zone of three rod lightning lines of the same height; Horizontal sectional protection area at levelh X.

1, 2, 3 - Lightning conductors

Fig. 12. The protection zone of four rod arbitrarily located lightning lines of the same height; Horizontal sectional protection area at levelh X.

1, 2, 3, 4 - Lightning conductors

Part of the three-time protection zone and more lightning consists of a height above 60 m, located outside the circles passing through the centers of the adjacent three-dimensions, truncated at a distanceD. h. from the top. Part of the zone located inside the circles does not stop. ValueD. h. Determined by formulas () and ().

Prerequisite for the protection of the entire area at the levelh X. is an:

for lightning lighters heighth.£ 30 m: D.£ 8 · h A.;

for lightning lighters height 30< h.£ 250 m: D.£ 8 · h A. · p.,

where D. - Diameter of the circle conducted through three adjacent lightning lines.

Cable Lighting Zones

The protection zone of a single cable lightning conduction (horizontally suspended cable) has the shape shown in Fig. For lightning lighters high up to 30 m and in fig. For lightning lines height from 30 to 250 m. Protection area at the levelh X.limited to two parallel lightning lines lines located at a distancer X. From the vertical plane passing through the cable lightning. This distance isr X., conventionally called by analogy with a single rod lightning conduction radius of protection, are determined by formulas:

h. < 30 м

(8)

for solitary cable lightning heighth. from 30 to 250 m

Fig. 13. The protection zone of a single cable lightning conductor with a height of up to 30 m:

A. - Horizontal sectional protection area at levelh X.; T. - Table

Fig. 14. Protection area of \u200b\u200ba single cable lightning conductor with a height of more than 30 m

Cable Lighting Rest Protection Zone 30< h.< 250 м усекается сверху на величину

Fig. 15. Normogram for calculating the system of protection of a single cable lightning conductor with a height of up to 30 m

Fig. 16. Nomogram for calculating a single cable lightning zone with a height of 30 to 100 m

Lightning heighth.defined by nomogram (Fig.) Compared with a critical height

for h. < h kr Lightning height is chosen equalh kr. The method of selecting the cable protection comes from the dependence of the probability of a lightning break from the corner of the cable protection (a. ) And the height of the supports of the VL. The correspondence between the outlined herein and in the section of the threats of the VL methodology is established by the ratiotG A \u003d. r X./ h A..

4. Construction of the protection zone of two parallel cable lightning systems is represented in Fig. and. The external areas of protection zone are defined as for a single cable lightningh. \u003e 30 m and truncated at a distanceD. h. from the top. The vertical section of the protection zone between two cable lightning lines is limited to the arc of the circle passing through the lightning conductors and the middle point between the lightning liftsO.inspected

(11)

where A. - distance between lightning lifts;

Fig. 17. The protection zone of two cable lightning lines 1 and 2 height up to 30 m:

I. - Horizontal section at the levelh X.; II - Vertical Section of the Protection Area

Fig. 18. The protection zone of two cable lightning systems with a height of more than 30 m

R \u003d 1 h.£ 30 m; nineteen . Around the lightning conduction 1 larger height is built a protection zone, as for a single lightning conduction. Next, through the vertex of the lightning conduction 2, a horizontal line is carried out up to the intersection with a lightning conduction zone 1. Taking this point of intersection for the top of some fictitious lightning conduction 3 of the same height as a smaller sweeping, the protection zone for two lightning systems is built 2 and 3, the outlines of which are limited The inner portion of the total protection zone.

Fig. 19. The protection zone of two lightning lines of different heights:

1, 2 - lightning conductors; 3 - Top of fictitious lightning conduction

For rod lightning lighters heighth. \u003e 60 m and cable h. \u003e 30 M protection zone at their top feces at a distanceD. h.from the vertex specifically for each of the lightning lines and in accordance with their type.

The total zone of protection of the cable and rod lightning conductions is determined by the imposition of their zones. The configuration of the protection zone at the end of the cable lightning conduction is also being built. At the same time, the end of the cable should be considered as a rod lightning resulting of the corresponding height.

The protection zones with a breakthrough probability of not more than 10 -2 are designed for open distribution devices of stations and substations, as well as for utility facilities in need of lightning protection. At the same time, the inputs of the devices and busbars must be in the depths of the protection zone, since the defeat of their lightning is the greatest danger.

The protection zones with a breakthrough probability are not more than 10 -3 are designed for high-responsive busbar sites, which, due to their high height or length, may be exposed to frequent lightning strikes.

The reliability of protection increases when placing objects in the inner part of the protection zone of multiple lightning systems.

Due to the probabilistic nature of lightning breakthroughs, the performance of lightning protection, fully excluding the defeat of protected objects, is not always appropriate, and in some cases it is technically not feasible. The optimal reliability of lightning protection is determined on the basis of the comparison of the cost of lightning protection and possible damage from lightning damage.

Reliability of lightning protection is characterized by the numberb. Lightning breakthroughs per year on a protected structure or number of years for which one breakthrough of lightning is expected in the protection zone

b \u003d ψ · n,

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

N. - the total number of shocks per year in a lightning conductor and a protected structure.

The expected number of lightning strikes and year in a single rising structure (including a rod lightning conductor) heighth. Meters:

N \u003d 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 h thunderstorm ,;

T. - average intensity of thunderstorm activities for the locality, h.

R. \u003d 3.5 · h. - The equivalent radius of the circle describing the area with which the construction "collects" lightning, m.

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

T \u003d. nts.· 10 -6, (13)

where S.- area, limited arcs of circles described by the radiusR. Around every lightning conduction, m 2.

The number of shocks per year in a long rising structure (including a cable lightning) heighth. and length l, (m):

N \u003d2 ntlr.· 10 -6, (14)

where R. = 3,5 h..

The number of blows into the construction structurel. (m), width m. (m) and height h. (m) is determined by the formula (), where

S \u003d.(l + 7 h.)(m +.7 h.). (15)

Protective action lightning conductor Based on "The zipper property is more likely to affect higher and well-grounded items compared with a number of lesser led objects. Therefore, by a lightning resulting, towering over the protected object, the lightning interception function is imposed, which would affect the object. Quantitatively protective action of the lightning It is determined through the probability of a breakthrough - the ratio of the number of lightning strikes into a protected object (breakthrough numbers) to a total number of shocks in a lightning resulting and an object.

According to the adopted settlement model, it is impossible to create perfect protection against direct lightning strikes, fully eliminating breakthroughs on the protected object. However, in practice, the mutual arrangement of the object and the lightning conduction, which provides a low probability of a breakthrough, for example, 0.1 and 0.01, which corresponds to a decrease in the number of lesions of the object by about 10 and 100 times compared to the object where there is no lightning discharge. For most modern objects, at such levels of protection, a small number of breakthroughs for the entire service life is ensured.

Fig. 11.22. Lightning device.

Supports of air LS protect against destruction with straight blows of lightning with rod lightning lines, which are installed on introductory, cable, control, cut, transitional supports, as well as on supports that are replaced due to thunderstorm damage. For a lightning conduction, a steel linear wire with a diameter of 4 ... 5 mm is used, the lower end of which is given. This removal is called the grounding. The discharge of the ground wire (Fig. 11.22) depends on the nature of the soil and can be equal to 1 ... 12 m. The depth of the grounding of the earthing is 0.10 m. The larger the resistivity of the soil, the greater should be the length of the grounding. On intermediate and angular supports, they usually do not make a removal, but bring wire to a commander.

Supports on which spark or gas-filled arresters are installed are also protected by lightning lines. Under the conditions of safety in supports that have an intersection or rapprochement with introduced, at an altitude of 30 cm from the ground, a gap is made, creating a spark gap of 50 mm long.

The efficiency of the lightning lifting is the greater, the higher it is located. The zone of protective action of the lightning conductor is determined by approximately the formula S \u003d πH2, where H is the height of the lightning conduction.

Ground-proof cable - grounded extended lightning conduction, stretched along the power line over the wires.

Depending on the location, the amount of wires on the supports of the VL, the resistance of the soil, the voltage class of the VL, the necessary degree of lightning protection, is mounted one or more cables. The height of the suspension of incremental cables is determined depending on the corner of protection, that is, the angle between the vertical passing through the cable, and the line connecting the cable with the extreme wire, which can vary widely and even be negative.

On the voltage of up to 20 kV, the lightning cables are usually not applied. 110-220 kV on wooden supports and 35 kV (regardless of the material supports) most often protect the cable only approaches to substations. Lines 110 kV and higher on metal and reinforced concrete supports are protected by a cable throughout.

Steel ropes are used as a lightweight ropes or sometimes - steel aluminum wires with a steel core of an increased cross section. Steel ropes are conventionally denoted by the letter with and numbers indicating the area of \u200b\u200btheir cross section (for example, C-35).

Fig. 21. Definition on the model of the zone of the rod lightning conduction

Fig. 22. Zone of 100% lesion of the rod lightning

Fig. 23. The zone of protection of a single rod lightning conductor height up to 60 m:
A - lightning height; HX - point height at the border of the protected area: H & -H-HX - active height of the lightning

This zone has received the name of the zone of 100% lesions of the rod lightning conduction. Secondly, around the lightning conduction height H, there is a zone that is not affected by the discharge. This zone is protected by a lightning conductor H. The minimum distance from the vertical of the aircraft, equal to r0 \u003d 3.5 / g, and is the radius of the zone of protection of the lightning conduction at the ground level.
The radius of the protection zone at any height of the lightning conduction H is also determined by experiments in the laboratory using the HX height rod (see Fig. 21), simulating the protected object and in one plane with the electrode A and the lightning conductor H. They move relative to each other. At different locations, a certain number of discharges is performed.
Then there is a maximum distance of GC between the HX height and the lightning conduction height h, at which the rod is not affected by the discharge. This distance of the GC is a radius of the zone of the lightning lifting at the height of HX.
Thus, the zone of lightning protection zone of a height of H is "tent" (Fig. 23), the radius of GC, M, which "guidelines for calculating the zerry and cable lightning zones" for lightning lighters height up to 60 m recommended to count
according to the formula

The basis of the cable lightning conduction, as follows from the name, is galvanized metallic (as a rule, steel) is used). It is recommended that the area of \u200b\u200bits cross section is not less than 35 square meters. mm.

Types and features

Cable lightning systems are used where other options are quite complex in installation, for example, on extended roofs and high-voltage lines. However, sometimes they are placed on small cottages.

One of the shortcomings of the cable lightning conduction is that the cable is noticeable on the roof, but if desired, it can be masked. In some situations, cable lightning lighters are permissible to stir not on the protected object itself, but near it.

Cable lightning protection occurs two types:

For a single enough just two masts, between which the cable is stretched. And each mast has a connection with its separate current, earthing and lightningness.

In certain cases, four masts are installed on the building. They are connected by two cables, and so that they are located in parallel to each other at one height.

When the lightning strikes, they act together as a single whole - this is a double cable thunder.

Nuances calculating

Designing a cable lightning conductor, as well as its installation, in most cases is a rather difficult task that requires access to professionals.

At the design stage, it is necessary to spend - that is, to determine the specific area of \u200b\u200baction and other parameters.

The calculation is carried out by fairly complex formulas in which the following indicators must be taken into account, in particular:

• cable support height;
• the width and length of the zone of the cable lightning conduction (both at the level of the structure and the ground level);
• expected damage to the amount of zipper per year.

Mounting itself should strictly comply with the rules of the electrical installation device (PUE), and therefore has many subtleties that an unprepared person may not know.

Installation

Cables connect with masts and recesses bolted clamps. You need two such clamps to each compound. If the roof is finished with igniting materials (plastic, wood, etc.), then the cables must be at a distance of 10-15 centimeters from the surface.

Cable extension is possible only by happiness with a length of overhearsow no meter one and a half meters. In order to protect the cable from the fluorime of lightning and make a more reliable grounding of the supports, a suspended insulator is used with the so-called spark gap.

In addition, some elements of future lightning protection should be combined with welding, and the weld cross section should be at least three times higher than the nominal cable cross section.

It is undesirable that the spans are more than 15 meters, to avoid this, it is recommended to establish additional supports. The support of the cable lightning conductor must be equipped with a small wire ring through which the cable will pass.

Supports and masts should be strong enough to withstand the weight of the structure with strong wind gusts. It is also worth remembering that the smaller the angle between the imaginary vertical passing through the cable and the line connecting the cable with the extreme wire (this is called a protective angle, and its value, according to standards, should be 20-30 degrees), the more effective will be the cable Lightning message.

Comparison with other options

In addition to the cable, there is also a rod and mesh lightning protection. The mesh is the most complicated, and the rod, like the cable, is satisfied with the design. A distinctive feature of the rod system is the presence of a vertical pin, which takes on the lightning.

Practice shows that they protect a much smaller area than cable, and therefore many stop in the second version of these two. It is a compromise between the usual pin (mast) and the grid.

Ultimately, the choice of one or another lightning protection will depend on the specifics of the building or structure, the state of the electrical appliances, such as the grounding of the electrical network, the frequency of the thunderstorm in the specific climatic zone.