Connecting lightning protection to ground. Lightning protection and grounding. Initial data about the building and the environment

In everyday life, every person has long been accustomed to using electrical appliances. It is quite difficult to imagine life without electrical engineering. In order not to face the threat of high voltage to health and life in the event of a malfunction of the equipment, it is required to install a lightning protection and grounding loop.

Grounding is carried out with special equipment that connects the elements of devices that are not intended to be energized to the ground.

In cases where the insulation of electrical appliances is broken, the current flows to elements that are not intended for it, including the body of the equipment.

Insulation breakdown can result in equipment failure, and if a person touches parts, you can get harm to health or death.

The ground loop allows most of the current to go to ground. To do this, it is necessary to observe the minimum resistance indicators.

Device

The scheme of the grounding device includes metal pipes, rods, which are interconnected by a metal wire with a deepening in the ground. The device is connected to the shield using a bus. The grounding structure should be located at a distance of no more than 10 m from the house.

To make a ground loop with your own hands, you can use any metal forms as electrodes that can be hammered into the ground and have a cross section of more than 15 sq. mm.

Metal rods are placed in a closed chain, the shape of which depends on the number of electrodes in the circuit. The structure should be deepened into the ground below the freezing level.

You can create a contour with your own hands from improvised materials, or purchase a ready-made device. Ready-made ground loop equipment is distinguished by high prices, but at the same time it is convenient to install and will last a long time.

Circuits are divided into two types:

traditional;
deep.

The traditional circuit is characterized by the location of one electrode from a steel strip in horizontally, and the rest are installed vertically, pipes or rods are used for them. They deepen the contour in that part that is less accessible to people, most often they choose the darkened side, in order to maintain a single environment.

The disadvantages of the traditional circuit system include:

complex execution of works;
grounding materials are prone to rust;
the environment of occurrence can create unacceptable conditions for the circuit.

The deep contour is devoid of most of the disadvantages of the traditional one; special equipment is used for it.

Has a number of advantages:

equipment meets all established standards;
long service life;
the environment does not affect the protective functions of the circuit;
ease of installation.

Loop installation requires a mandatory check of the entire grounding system. It is necessary to verify the quality of the work performed, to verify the strength of the circuit, if there are any unconnected parts.

It is obligatory to conduct research from licensed specialists. For the installed ground loop, a passport, an inspection protocol and an act of admitting equipment to work are issued. The ground loop must comply with the standards set out in the PUE.

Grounding for transformer

For grounding the transformer booth, an external or internal circuit is used, the choice of option depends on the design features.

The outer contour is created for a substation consisting of one chamber.

The scheme of the equipment consists of vertical rods and a horizontal steel strip. The dimensions of the horizontal earth electrode are 4x40 mm.

The resistance index for the circuit should be no more than 40, for the earth it should not exceed 1000. Based on the indicated parameters, the circuit should consist of 8 electrodes with dimensions of 5 m and a cross section of 1.6 cm. The circuit should run no closer, than a meter from the walls of the building where the substation is located. The depth of the ground loop is 70 cm.

To create lightning protection for the transformer, the roof is connected to the ground loop using an eight-millimeter wire.

If the substation consists of three chambers, then a strip from the contour is installed around the entire perimeter of the components. This measure allows you to secure all elements of the metal structure.

To do this, the ground bus is fixed with the help of holders at a distance of more than half a meter between them. The distance from the surface should be 40 cm. The contour elements are welded or bolted. For a solid connection, a wire without insulation is used. Grounding conductors are laid through the wall and painted green, on which yellow stripes are made at a distance of 15 cm.

Grounding for a three-phase network

If the house uses a network with a voltage of 220 V, then grounding is not necessary, you can limit yourself to grounding the equipment.

A ground loop for houses with a 380 V network is required.

The difference between the two loop systems lies in the resistance values for the network. In the case of 220 V, the resistance should be no more than 30 ohms; for a three-phase network, the indicator varies from 4 to 10 ohms. This is related to the level of earth resistivity. The soil in different areas has a different composition, and therefore each soil has its own resistance indicators.

Before performing work, an accurate calculation should be carried out for the circuit in order to calculate the number of required grounding conductors for the network.

The calculation is made according to the formula R=R1/KxN, where R1 is the resistance of the electrode, K is the coefficient characterizing the load on the network, N is the number of electrodes in the circuit.

To create a circuit for a three-phase network, special attention must be paid to materials, because. this network is demanding on the quality of grounding.

The choice should be based on the following requirements:

if the function of the electrode is performed by a pipe, then its wall should be no thinner than 3.5 mm;
when choosing a corner, pay attention to the thickness, which should be at least 4 mm;
cross-sectional diameter of the pins is not less than 16 mm;
the connecting strip between the grounding conductors must meet the dimensions of 25x4 mm.

The installation of the circuit is carried out around the perimeter, its shape can be any, depending on the number of electrodes. Most often performed in the form of a triangle. Grounding equipment is screwed into the ground to a depth of half a meter.

The distance between the corners, which is equal to the length of one earth electrode. The connection to the strip is made with bolts or by welding.

At the end of the installation work, the office is connected to the bus and connected to the switchboard. An example of a ground loop is shown in the photo.

The creation of systems for protecting electrical appliances from the effects of unwanted voltage and natural phenomena such as lightning is an important point. The measures taken make it possible to protect a person from the harmful effects of current, as well as to avoid damage to equipment.

The creation of ground loops and lightning protection is possible with your own hands. It is important that the ground loop meets the requirements of the PUE and accepted standards. The quality of materials and workmanship is reflected in the level of protection of electrical appliances. Incorrect execution can cause more voltage to be output, which will cause harm.

The lightning protection circuit is a complex system for protecting an object from direct lightning strikes: lightning rod, down conductor, grounding. The classical scheme proposed by Benjamin Franklin back in 1752 underlies all modern lightning protection systems. Proven technology, combined with the latest equipment, professional design and installation, provides almost one hundred percent protection against lightning strikes!

Lightning protection contour of buildings and structures

Lightning rods

Rod lightning rod. Metal rods are installed on the roof or at the highest points. To increase the height of the structure, special metal masts are used. For large objects, it is recommended to arrange several separate rods along the perimeter with autonomous down conductors.
Rope lightning rod. Lightning strikes a cable stretched between supports. The technology is appropriate for extended objects. A typical example is power lines, which are protected by lightning rods.
Lightning mesh. The system is used mainly on flat roofs: a metal mesh is arranged over the entire area in increments of up to 5x5 m. It should be noted that the mesh does not protect protruding objects, such as antennas or chimneys. That is why rods are also included in the lightning protection scheme, including them in a common circuit.

In addition to classical solutions, active lightning rods are used. Devices ionize the air, provoke a lightning strike. Due to this, it is possible to reduce the number of lightning rods and the overall height of the lightning protection circuit.

Down conductors

Aluminum or steel conductor, the main task of which is to transfer current from the lightning rod to the ground electrode. As a rule, external down conductors are installed on buildings, but in some cases, according to the RD instructions, it is allowed to use building structures, for example, reinforcement in reinforced concrete blocks. However, this is unacceptable in the presence of highly sensitive electronics: the electromagnetic field created during the passage of the discharge can damage the equipment.

For the down conductor, a conductor with a cross section of 6 mm is used, all connections are welded. In places where contact with a person is possible, the cable must be isolated. In addition, there must be direct access to the down conductor for regular inspections.

grounding

So, the lightning rod received the discharge and transmitted it through the down conductor to the ground electrode or ground loop - several vertical electrodes installed in the ground and connected to each other by a horizontal conductor. The sole purpose of a grounding device is to dissipate the resulting current into the ground. To save space, the contour is usually formed along the perimeter of the object, but not closer than 1 m to the foundation. The RD instruction requires at least 3 electrodes in the circuit, however, modern technologies offer the most effective solution: the installation of a composite depth electrode. Due to the immersion to a depth of up to 30 meters, to achieve the required resistance threshold, it is enough to install one earth electrode.

Calculation of the lightning protection circuit

Correctly calculating and designing lightning protection is a key task to ensure the safety of a building from direct lightning strikes. For complex objects, as well as systems exceeding 150 m in height, the calculation is performed using special computer programs. For all other buildings and structures, instructions SO 153-34.21.122-2003 provide standard formulas for calculations.

The protection zone for a circuit with rod lightning rods is a cone in which the highest point coincides with the top of the lightning rod. The protected object must completely fit into the protective cone. Thus, the protection zone can be increased by raising the lightning rod or installing additional rods.

According to a similar principle, the contour of the cable lightning protection is also calculated. In this case, a protective trapezoid is obtained, the height of which is the distance between the cable and the ground.

Ground loop resistance

Grounding resistance is measured in ohms, and ideally should be 0. However, in practice, the value is unattainable, so the maximum threshold for lightning protection is set to no more than 10 ohms. However, the value depends on the resistivity of the soil, therefore, for sandy soils, where this parameter reaches 500 Ohm / m, the resistance increases to 40 Ohm.

Combining the ground loop and lightning protection

In accordance with paragraph 1.7.55 of the Electrical Installation Code for equipment and lightning protection of buildings of category II and III, in most cases, a common ground loop is arranged. However, it is necessary to distinguish between types of grounding:

Protective - for the electrical safety of equipment.
Functional - a necessary condition for the correct operation of special equipment.

It is forbidden to combine functional grounding with a protective or grounding conductor of a lightning rod: there is a risk of high potentials entering and failure of sensitive equipment.

In this case, it is possible to combine grounding for a lightning rod and protection of electrical equipment or arrange it separately, but connect it to each other through a special clamp for potential equalization.

Designing lightning protection is a responsible and complex task. Entrust the protection of your home or office to professionals, contact the experienced specialists of our company! You can get advice on the website or by phone.

The need to electrically connect the ground loop of lightning protection installed directly on the building with the ground loop for electrical installations is prescribed in the current regulatory documents (PUE). We quote verbatim: "Grounding devices for protective grounding of electrical installations of buildings and structures and lightning protection of the 2nd and 3rd categories of these buildings and structures, as a rule, should be common." Just the 2nd and 3rd categories are the most common, the 1st category includes explosive objects to lightning protection of which increased requirements are imposed. However, the existence of the phrase "as a rule" implies the possibility of exceptions.

Modern office and now residential buildings contain many engineering life support systems. It is difficult to imagine the absence of ventilation systems, fire extinguishing, video surveillance, access control, etc. Naturally, the designers of such systems have concerns that as a result of the action of lightning, “delicate” electronics will fail. At the same time, practitioners have some doubts about the expediency of connecting the contours of two types of grounding and there is a desire "within the law" to design electrically unrelated groundings. Is such an approach possible and will it actually increase the safety of electronic devices?

Why is it necessary to combine ground loops?

When lightning strikes a lightning rod, a short electrical impulse with a voltage of up to hundreds of kilovolts occurs in the latter. With such a high voltage, a breakdown of the gap between the lightning rod and the metal structures of the house, including electric cables, can occur. The consequence of this will be uncontrolled currents that can lead to fire, electronics failure, and even destruction of infrastructure (such as plastic water pipes). Experienced electricians say: "Give lightning a way, otherwise it will find it itself." That is why the electrical connection of earths is mandatory.

For the same reason, the PUE recommends electrically combining not only groundings located in the same building, but also groundings of geographically adjacent objects. This concept refers to objects whose groundings are so close that there is no zone of zero potential between them. The combination of several groundings into one is carried out, in accordance with the norms of PUE-7, clause 1.7.55, by connecting the ground electrodes with electrical conductors in the amount of at least two pieces. Moreover, the conductors can be both natural (for example, metal elements of the building structure) and artificial (wires, rigid tires, etc.).

One common or separate grounding devices?

Earthing conductors for electrical installations and lightning protection have different requirements, and this circumstance can be a source of some problems. A grounding conductor for lightning protection must divert a large electric charge into the ground in a short time. At the same time, according to the "Instructions for lightning protection RD 34.21.122-87", the design of the ground electrode is standardized. For a lightning rod, according to this instruction, at least two vertical or radial horizontal ground electrodes are required, with the exception of lightning protection category 1, when three such pins are needed. That is why the most common grounding option for a lightning rod is two or three rods, each about 3 m long, connected by a metal strip buried at least 50 cm into the ground. When using parts manufactured by ZANDZ, such a grounding device turns out to be durable and easy to install.

A completely different matter is grounding for electrical installations. In the normal case, it should not exceed 30 ohms, and for some applications described in departmental instructions, for example, for cellular equipment, 4 ohms or even less. Such grounding conductors are pins more than 10 m long or even metal plates placed at a great depth (up to 40 m), where even in winter there is no freezing of the soil. To create such a lightning rod with the deepening of two or more elements by tens of meters is too expensive.

If the soil parameters and the requirements for resistance make it possible to perform a single grounding in a building for a lightning rod and grounding of electrical installations, there are no obstacles to doing it. In other cases, various ground loops are made for lightning rods and electrical installations, but they must be connected electrically, preferably in the ground. An exception is the use of some special equipment that is particularly sensitive to interference. For example, sound recording equipment. Such equipment requires a separate, so-called technological grounding device, which is directly indicated in the instructions. In this case, a separate grounding device is made, which is connected to the potential equalization system of the building through the main grounding bus. And, if such a connection is not provided for by the instruction manual for the equipment, then special measures are taken to prevent people from simultaneously touching the specified equipment and the metal parts of the building.

Electrical connection of earths

A circuit with several earths connected electrically provides for the fulfillment of different, sometimes conflicting, requirements for earthing devices. According to the PUE, grounding, like many other metal elements of the building, as well as the equipment installed in it, must be connected by a potential equalization system. Potential equalization refers to the electrical connection of conductive parts to achieve potential equality. Distinguish between the main and additional potential equalization systems. Groundings are connected to the main potential equalization system, that is, they are interconnected through the main grounding bus. The wires connecting the grounds to this bus must be connected according to the radial principle, that is, one branch from the specified bus goes to only one ground.

In order to ensure the safe operation of the entire system, it is very important to use the most reliable connection between the grounds and the main ground bus, which will not be destroyed by lightning. To do this, you must comply with the rules of the PUE and GOST R 50571.5.54-2013 “Low-voltage electrical installations. Part 5-54. Grounding devices, protective conductors and potential equalization protective conductors” regarding the cross section of the potential equalization system wires and their interconnection.

However, even a very high-quality potential equalization system cannot guarantee the absence of voltage surges in the network when a lightning strikes a building. Therefore, along with well-designed ground loops, surge protection devices (SPDs) will save you from problems. Such protection is multistage and selective. That is, a set of SPDs should be installed on the object, the selection of elements of which is not an easy task even for an experienced specialist. Fortunately, ready-made SPD kits are available for typical applications.

conclusions

The recommendation of the Electrical Installation Code on the electrical connection of all ground loops in the building is reasonable and, if implemented correctly, not only does not create a danger to complex electronic equipment, but, on the contrary, protects it. In the event that the equipment is sensitive to lightning interference and requires its own separate earthing, a separate process earth can be installed in accordance with the manual supplied with the equipment. The potential equalization system, which combines disparate ground loops, must provide a reliable electrical connection and largely determines the overall level of electrical safety at the facility, so special attention should be paid to it.

2.2. What is the purpose of grounding a lightning rod

Please do not consider the title of the section banal. Lightning rods have always been grounded since their invention, otherwise how could they divert the lightning current to the ground. Modern manuals say that the grounding resistance must provide safe discharge of lightning current. What danger and safety are we talking about? Here it will not be possible to dissuade platitudes. Probably, it is worth remembering once again about overhead power lines. There, the grounding resistance determines the resistive component of lightning surges that act on the string of insulators.

There is nothing similar for lightning rods. Their lightning rod ”no problem” accepts the potential of the ground electrodes. The presence of a finite ground resistance does not affect the ability of a lightning rod to attract lightning to itself. In the laboratory, they repeatedly tried to trace the influence of grounding resistance on this process, and each time to no avail. The explanation here is quite simple and obvious. Lightning never strikes a lightning rod. It is met and attracted by the plasma channel of the counter-discharge, which starts from the top of the lightning rod in the electric field of the thundercloud and the charge of the already forming lightning. This channel (it is called a counter leader) develops at a current of no more than tens of amperes. The voltage drop from such a weak current on the grounding resistance of the lightning rod is not significant compared to the potential of the order of 10 7 -10 8 V, which is carried by lightning from a thundercloud. Indeed, with a grounding resistance of 10, 20, 100 or 200 Ohm, the voltage on the ground electrode from a current of ~ 10 A will still not exceed even 10 4 V - a value negligible compared to what lightning has.

A stand-alone lightning rod, as you know, is used for the sole purpose of eliminating the spread of lightning current through the metal structures of the protected object. It is for this purpose that quite specific distances from the lightning rod to the object are chosen in the air and on the ground. Let's assume that they are chosen correctly and really exclude spark overlaps. Nevertheless, the current enters the object's grounding conductor and enters it in a significant proportion, especially when the function of its grounding is performed by the foundation of the protected structure, which is quite large in area. The calculated data in fig. 14 show this proportion depending on the distance between the ground electrodes. At the lightning rod, it is made in accordance with the instructions of Instruction RD 34.21.122-87 in the form of a horizontal strip 10 m long with 3 vertical rods of 3 m each; the foundation of the object has dimensions of 50x50 m and is buried by 3 m. Computer calculations are made for homogeneous soil and for the case when the surface layer of the main soil to a depth of 2.5 m is replaced by a highly conductive one with a resistivity 50 times lower. It is easy to see that the insulation distance of 5 m, prescribed by the standard of OAO Transneft, does little to prevent the penetration of lightning current to the object through the ground, especially if its top layer is replaced or chemically treated. Even at a distance of 15 m, normalized by the Gazprom standard, the current in the ground electrode system of the facility exceeds 50%.

Figure 14. The fraction of the lightning current that penetrated into the object's grounding conductor through a conductive connection with the lightning rod's ground electrode, depending on the distance between them

Here it should be emphasized once again that any treatment of the upper soil layer, which reduces the ground resistance, not only does not reduce the conductive connection between the lightning rod and the object, but significantly strengthens it, thereby increasing the share of the lightning current branched into the object.

It's time to once again raise the question of the goal of reducing ground resistance. There are two untouched aspects of the problem - the formation of spark channels and the step voltage. The first question will be discussed below in a special section. As for the step voltage, it certainly depends on the design of the grounding conductor of the lightning rod and on its grounding resistance. The calculated curves in Figs. 15 demonstrate the dynamics of the step voltage decrease as the lightning rod is removed from a typical ground electrode, prescribed by Instruction RD 34.21.122-87 (see explanations for Fig. 14).

2.3. How to design

The section again sets the task of meeting the requirements of regulatory documents without unjustified material costs. This is all the more important because the grounding resistance value of the lightning rod has little effect on the quality of external lightning protection. In any case, those dangerous effects of lightning are not directly related to it, which can lead to a catastrophic situation at a tank farm or any other hydrocarbon fuel processing facility. Most importantly, I would very much like to avoid expensive chemical treatment or replacement of large volumes of soil and without them meet the requirements of industry standards for lightning protection.

It is advisable to create a ground electrode for each lightning rod separately only in soils with low resistivity, where even a typical design from RD 34.21.122-87 is quite capable. For example, with a horizontal bus length of 12 m recommended there and 3 vertical rods of 5 m each, the grounding resistance in the soil with specific resistance ρ is equal to

This means that at ρ ≤ 300 Ohm m the calculated value will not exceed 20 Ohm. With a higher specific soil resistance, 4 mutually perpendicular beams provide a good result. With a length of 20 m, each grounding resistance is equal to

and the installation of 5-meter vertical rods at the ends of each of the beams reduces this value to

The problem becomes serious when the soil resistivity noticeably exceeds 1000 Ohm*m. Here attention is drawn to the organization of a single ground loop for all separate lightning rods. It is worth referring again to Fig. 4, which demonstrates the protection of the tank farm with 3 cables 100 m long, with a distance between parallel cables of 50 m. Combining their supports with horizontal tires forms a ground loop with two cells 100x50 m. Its grounding resistance when laying the tires to a depth of 0.7 m provides

which makes it possible to solve the problem in the ground with a resistivity of up to 3000 Ohm*m, even if guided by the Gazprom standard. It is appropriate to note that the additional arrangement of a local grounding device for each of the lightning rods has almost no effect on the grounding resistance of the formed loop as a whole. Thus, the use as a local ground electrode of each lightning rod of its foundation post with metal reinforcement 5 m long and an equivalent radius of 0.2 m (R gr ≈ 0.1ρ [Ohm]) in a system of 6 posts reduced the total resistance of the ground loop by only 6%. The reason for such a weak effect lies in the effective screening of the rods by extended horizontal tires. By extending the horizontal busbars connecting the supports of the lightning rods, it is possible to achieve a grounding resistance of about 20 ohms and in the soil with a specific resistance of 5000 ohms.

The reader has the right to interrupt the description of such rosy prospects, recalling that a long bus slowly enters the process of spreading the pulsed current due to its inductance. There is nothing to object to this. But at least two circumstances still operate in favor of the proposed solution. Firstly, none of the mentioned standards require any specific values of impulse ground resistance, and secondly, in high-resistance soils, the rate of penetration of impulse current into the ground bus is quite high, and therefore the current value of ground resistance R gr (t) = U gr (t)/i M (t) quickly takes on a steady value controlled by regulatory requirements. As an example in fig. 16 shows the calculated dynamics of changes in the grounding resistance of a busbar 200 m long between the supports of lightning rods. It is assumed that the soil resistivity is 5000 Ohm*m, and its relative dielectric constant is 5 (it is important to take this parameter into account when the capacitive leakage into the soil is comparable to the conductive one).

E. M. Bazelyan, Doctor of Technical Sciences, Professor
Energy Institute named after G.M. Krzhizhanovsky, Moscow

Useful materials:

grounding- these are the connections of a part of the electrical network or equipment with a grounding device. The grounding device is a ground electrode - a conductive part that is in contact with the ground. The grounding conductor can be in the form of metal elements of complex shape.

The quality of grounding is determined by the value of the resistance of the grounding device, which can be reduced by increasing the area of the ground electrodes or the conductivity of the medium. The electrical resistance of the grounding device is provided for in the project in accordance with the requirements of the Electrical Installation Rules.

Such a ground loop is installed in a building-free zone of the site. Grounding is subject to:

household electrical appliances with a unit power of more than 1.3 kW;
metal cases of bathtubs and shower trays (they must be connected with metal conductors to water pipes);
metal housings of networkers built-in or installed in suspended ceilings made using metal;
metal cases of household air conditioners.

Grounding switches are installed before the start of electrical work. The connection of the reinforcement of the foundations with the reinforcement of the walls must be carried out by the construction organization. Grounding switches are connected to pipelines by welding or a clamp. If it is not possible to use natural earth electrodes, artificial earth electrodes are used. These include a ground loop, which is created both for grounding electrical appliances and for lightning protection.

Lightning protection is a system of devices that ensures the safety of the building during electrical discharges in the atmosphere. Its main task is to change the trajectory of lightning discharges and extinguish its energy. Lightning protection includes:

lightning rod - a device that receives a lightning discharge;
current collector - elements of distribution of an electric discharge;
earthing switch - a device for extinguishing an electric discharge.

There are several lightning protection schemes. Scheme based on a lightning rod includes a metal rod connected by cables to a ground electrode. Lightning rod based on "spatial grid" installed on the roof of the house. It distributes and extinguishes the discharge in the event of a direct hit. Scheme based on tension systems similar to the scheme of a rod lightning rod, but the conductors are stretched along the perimeter of the protected zone.

All of the above structures are made of steel rods, ropes or steel meshes (at least 6 mm in diameter). Elements in nodes are connected by welding. The design of rod lightning rods is the most common, since they are the easiest to manufacture and ensure the reliability of the system.

Lightning rods based on tension systems are used when constructing roofs of complex shape. Spatial mesh requires more material and is more difficult to install. This type of lightning rod is appropriate if the roof of the house is higher than other objects located within a radius of 50 m.

Equivalent specific soil resistance ρ, Ohm*m	Maximum allowable resistance support grounding according to PUE, Ohm

More than 100 to 500
More than 500 to 1000
More than 1000 to 5000