Lightning protection and grounding circuits. Design and installation of lightning protection and grounding Re-connection of working grounding and lightning protection circuit

Country cottages, houses, as well as buildings located on the territory of your site, for safety reasons, must be connected to a grounding system, a potential equalization system. If grounded, electric shock can be prevented. Here you need to correctly calculate the load and install the grounding with the help of specialists by installing the grounding system into the ground. Installation of a grounding loop is a prerequisite for safety in a private home and buildings on your territory. According to the PUE (Electrical Installation Rules), grounding is a deliberately made connection of electrical installations, devices and equipment with a grounding structure.

The grounding device must be made in accordance with Chapter 1.7 of the Electrical Installation Rules and SNiP 3.05.06-85 “Electrical Devices”. Horizontal grounding conductor, attach to vertical grounding conductors with a deviation of 50-60 mm from the upper edge of the grounding conductor made of steel angle. Grounding conductors are located at a distance of at least 0.5 m from the foundation of the building, away from the doors. Places welded joints should be painted with durable paint to prevent corrosion and rust. The grounding loop should be inserted into the building using a conductor made of round steel with a diameter of at least 6 mm, using thick-walled gas pipelines at intersections with building structures metal pipes. It is recommended to enter the building at a height of 0.5 m from the ground surface of the building foundation. If, when installing a grounding device, its resistance value turns out to be more than 10 Ohms, then additional grounding conductors should be installed, bringing the resistance to the standard Rз< 10 Ом.

Also, do not neglect safety and install a potential equalization system in the electrical installation of the building. Installation of a potential equalization system is a significant reduction in the potential difference between open conductive parts accessible to simultaneous contact, third-party conductive parts, grounding and protective conductors, as well as PEN conductors by forcibly connecting these parts to each other.

Potential equalization will make the location where a person lives, free from the appearance of potential differences, and will protect residents and those in the room from shock electric shock. Literally all conductive parts of electrical and non-electrical equipment, building metal structures must be connected to each other.

Those elements that for some reason cannot be added to common system potential equalization must be isolated from other equipment in such a way that they cannot be touched at the same time. The insulation may have been damaged. Accordingly, the voltage that arises on one of the accessible conductive parts and all conductive parts accessible to touch at the same time must acquire the same voltage in order to avoid the occurrence of a voltage difference that is dangerous to humans. In the case where one of the accessible parts is ground, all surrounding equipment should be connected to ground through the lowest possible resistance.

Grounding work consists of several stages. First, determining the installation location of the circuit, avoiding possible intersections of underground communications. The choice of material from which the circuit itself will be made in the future, a metal or copper rod driven into the ground. Pricing for installation of a grounding loop may vary, it all depends on each individual situation. Starting from completing the task on our own, viewing a large number of information, without knowledge and skill, in achieving one hundred percent correct result. Or save yourself from headaches and doubts about the correctness of the work done, leave the calculation and implementation of the grounding loop to professional electricians. The calculations have been completed, the metal structures are installed in a previously prepared trench and connected to the house.

Lightning protection.

Nature constantly amazes humanity amazing phenomena. The power and uncontrollability of lightning is fascinating and at the same time conceals a number of dangerous things for humans. The consequences of a lightning strike can be very diverse, ranging from a charred piece of land to a disastrous outcome. Lightning carries enormous destructive power, and when it hits a house, it leaves irreparable consequences. To protect and prevent damage to your home and property due to such a disaster, lightning protection is required in a private home. Lightning is a natural discharge of electricity that occurs in the lower layers of the earth's atmosphere, and quite seriously damages power lines of houses and other buildings. A lightning strike occurs very quickly, the lightning discharge reaches the ground at crazy speed.

Modern buildings, as well as equipment and machinery produced using new technologies, have become more attractive to lightning discharges. For example, items such as Cell Phones, antennas and other wireless equipment. However, at present, knowledge and technology make it possible to counteract this phenomenon and increase the chances of safety for private homes and nearby buildings. Lightning protection is aimed at ensuring the safety of buildings and people in them from the dangerous effects of lightning. Lightning rods are used as a protective measure. Such devices include several main components. Grounding loop, according to the PUE (Electrical Installation Rules), grounding is a deliberately made connection of electrical installations, instruments and equipment with a grounding structure. A lightning rod consists of a rod lightning rod that absorbs a lightning strike, a down conductor and an lightning rod with a grounding conductor that conducts lightning to the ground. An air terminal is a metal element for receiving electrical discharges. It can be installed on the roof of a residential building. The lightning rod must be fixed at the highest point of the roof. If the roof area is very large or has a complex configuration, you will need to install additional lightning rods.

1. According to the instructions “On the installation of lightning protection of buildings and structures” (No. RD - 34.21.122 - 87) and taking the degree of fire resistance of the building - category 3, we use a lightning rod for lightning protection of the building.

2. The lightning rod consists of:

• a rod lightning rod that receives a lightning strike;
• a down conductor connecting the lightning rod to the grounding conductor;
• a grounding conductor that conducts lightning into the ground.

3. Lightning rods (2 pcs.) are installed on existing brick pipes. The height of the lightning rod in relation to the highest point of the roof must be at least 0.25 m.

4. Connect the lightning rod to the down conductor and grounding conductor by welding.

5. Lightning rods and down conductors, as well as places of welded joints should be painted with durable paint to prevent corrosion and rust.

6. Grounding conductors are located at a distance of at least 0.5 m from the foundation of the protected building, away from the doors.

7. Connect the horizontal grounding conductor to the vertical grounding conductors with a deviation from the upper edge of the grounding conductor and the steel angle by 50.0 - 60.0 mm.

8. Lay the down conductor close to the surface of the roof and walls of the building.

9. Entry into the building from the grounding loop to the GZSh (main grounding bus) should be made with round steel conductors with a diameter of at least 6 mm from 2 opposite connection points on the grounding loop, using thick-walled gas-supply metal pipes at the intersections with building structures. It is recommended to enter the building at a height of 0.5 m from the ground surface at the foundation of the building.

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 a high voltage threat to health and life in the event of equipment malfunction, it is necessary to install a lightning protection and grounding circuit.

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

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

The result of an insulation breakdown can result in equipment failure, and if a person touches the parts, it can cause harm to health or death.

The ground loop allows most of the current to flow into the ground. To do this it is necessary to comply minimum indicators resistance.

Device

The grounding device circuit includes metal pipes and rods, which are connected to each other by metal wire buried in the ground. The device is connected to the panel using a bus. The grounding structure should be located at a distance from the house of no more than 10 m.

To make a grounding loop with your own hands, you can use any electrodes. metal molds, which can be driven into the ground and have a cross-section of more than 15 sq. mm.

Metal rods are arranged 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 scrap materials, or purchase a ready-made device. Finished ground loop equipment is different high prices, but at the same time it is convenient to install and will last a long time.

Contours are divided into two types:

1. traditional;
2. deep.

A traditional circuit is characterized by the arrangement of one electrode made of a steel strip in horizontally, and the rest are installed vertically; pipes or rods are used for them. They deepen the contour in the part that is less accessible to people, most often choosing the darkened side to maintain a unified environment.

The disadvantages of the traditional circuit system include:

• complex execution of work;
• grounding materials are susceptible to rust;
• the underlying environment may create conditions that are unacceptable 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:

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

Installation of the circuit requires a mandatory check of the entire grounding system. It is necessary to verify the quality of the work performed, make sure the strength of the circuit, and whether there are any unconnected parts.

It is mandatory to conduct research from licensed specialists. For the installed grounding loop, a passport, inspection protocol and certificate of equipment approval for operation are drawn up. The grounding circuit must comply with the standards set out in the PUE.

Grounding for transformer

To ground the transformer booth, an external or internal circuit is used; the choice of option depends on the design features.

The external circuit is created for a substation consisting of one chamber.

The equipment diagram consists of vertical rods and horizontal steel strip. The dimensions of the horizontal ground electrode are 4x40 mm.

The resistance indicator for the circuit should be no more than 40, for the ground it should not exceed 1000. Based on the specified parameters, the circuit should consist of 8 electrodes with dimensions of 5 m and a cross-section of 1.6 cm. The circuit should lie no closer than less 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 a transformer, the roof is connected to the ground loop using an eight-millimeter wire.

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

To do this, attach the grounding bus using 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 together. For a seamless connection, a wire without insulation is used. Grounding conductors are laid through the wall and painted green color, on which yellow stripes are made at a distance of 15 cm.

Grounding for 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 grounding circuit for houses with a 380 V network is required.

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

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

The calculation is made using the formula R=R1/KxN, where R1 is the electrode resistance, K is a 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, you need Special attention pay attention 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;
• the 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 circuit is installed around the perimeter; its shape can be any, depending on the number of electrodes. Most often performed in the shape 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 ground electrode. The connection to the strip is made using bolts or welding.

After completing the installation of the office, a busbar is attached to it and connected to the distribution panel. An example of a grounding loop is shown in the photo.

Creation of systems for protecting electrical appliances from unwanted voltage and natural phenomena like lightning is 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.

Creating grounding loops and lightning protection is possible with your own hands. It is important that the grounding 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. Improper execution may allow more voltage to be released which will cause harm.

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

Lightning protection circuit for 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 install several free-standing rods around the perimeter with autonomous down conductors.
• Cable lightning rod. Lightning strikes a cable stretched between supports. The technology is suitable for extended objects. A typical example is power lines, which are protected with cable lightning rods.
• Lightning protection mesh. The system is mainly used on flat roofs: arranged throughout the entire area metal grid in increments of up to 5x5 m. It is worth noting that the mesh does not protect protruding objects, such as antennas or chimneys. That is why rods are also included in the lightning protection circuit, including them in a common circuit.

Besides classic solutions, active lightning rods are used. The devices ionize the air and provoke a lightning strike. Thanks to this, it is possible to reduce the number of lightning rods and the overall height of the lightning protection circuit.

Down conductors

An aluminum or steel conductor, the main task of which is to transmit 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, the use of building structures, for example, fittings in reinforced concrete blocks. However, this is unacceptable in the presence of highly sensitive electronics: the electromagnetic field created during the passage of a discharge can damage the equipment.

A conductor with a cross section of 6 mm is used for the current conductor; all connections are welded. In places where human contact is possible, the cable must be insulated. In addition, there must be direct access to the down conductor for regular inspection.

Grounding

So, the lightning rod received the discharge and transmitted it along 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 around the perimeter of the object, but no closer than 1 m to the foundation. The RD instruction requires the presence of at least 3 electrodes in the circuit, however, modern technologies offer the most effective solution: installation of a composite depth electrode. Thanks to immersion to a depth of up to 30 meters, installing one ground electrode is sufficient to achieve the required resistance threshold.

Calculation of lightning protection circuit

Correctly calculating and designing lightning protection are key tasks 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 fit completely within the protective cone. Thus, the protection zone can be increased by raising the lightning rod or installing additional rods.

The contour of cable lightning protection is calculated using a similar principle. 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 equal to 0. However, in practice, the value is unattainable, therefore the maximum threshold is set for lightning protection - no more than 10 Ohms. However, the value depends on the soil resistivity, so for sandy soils, where this parameter reaches 500 Ohm/m, the resistance increases to 40 Ohms.

Combining the grounding loop and lightning protection

In accordance with paragraph 1.7.55 of the PUE for equipment and lightning protection of buildings of categories II and III, in most cases a common grounding loop is installed. However, it is necessary to distinguish between types of grounding:

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

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

In this case, you can combine the grounding for the lightning rod and the 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. Trust the professionals to protect your home or office, contact the experienced specialists of our company! You can get advice on the website or by phone.

Here again we have to omit Instruction SO-153-34.21.122-2003, which does not contain any specific requirements for grounding lightning rods. Instruction RD 34.21.122-87 formally formulates the requirements, but they relate not to the value of grounding resistance, but to the design of grounding devices. For free-standing lightning rods we're talking about about the foundations of lightning rod supports or about a special grounding conductor, the minimum dimensions of which are shown in Fig. 7.

Figure 7. Minimum dimensions grounding electrode made of a horizontal strip and three vertical rod electrodes according to RD 34.21.122-87

The standard does not contain any instructions on changing the size of the electrodes depending on the soil resistivity. This means that, according to the compilers standard design recognized as suitable for any soil. How much its grounding resistance R gr will change can be judged from the calculated data in Fig. 8.

Figure 8. Calculated value of the grounding resistance of a typical ground electrode from Instruction RD 34.21.122-87

A change in the value of R gr within almost 2 orders of magnitude can hardly be regarded as normalization. In fact, the standard does not contain any specific requirements for the value of grounding resistance, and this issue certainly deserves special consideration.

The Transneft JSC standard surprised us with a table of normalized grounding resistance values ​​for lightning rods (Fig. 9), which the compilers completely copied from the latest edition of the PUE, where it applies to grounding conductors for overhead line supports of 110 kV and above. The stringent requirements of the PUE are quite understandable, since the grounding resistance of the overhead line support largely determines the magnitude of the lightning overvoltage on the linear insulation. It is impossible to find out the reasons for transferring these requirements to the grounding of lightning rods, especially since in high-resistivity soils they generally cannot be implemented using any reasonable designs. To demonstrate this, in Fig. Figure 10 shows the results of calculating a lightning rod ground electrode of an absolutely fantastic design. It is an all-metal structure with a square cross-section, the side length of which is indicated on the x-axis. Two options have been calculated - with a depth of placement in the soil of 3 and 10 m. It is easy to verify that in soil with a resistivity ρ = 5000 Ohm m, the normalized value of 30 Ohm (R З /ρ = 0.006 m -1) will require filling the vicinity of the lightning rod foundation with metal with more than 50x50 m. The situation with an extended ground electrode is no better. Under the same conditions, to ensure the required grounding resistance, a horizontal bus more than 450 m long is needed.

Table 9

Figure 10. To assess the possibilities of meeting the requirements of the Transneft standard using a concentrated grounding device

The requirements of the Gazprom standard are extremely specific. The grounding resistance of a free-standing lightning rod for protection levels I and II should be equal to 10 Ohms in soils with ρ ≤ 500 Ohm m. In higher-resistivity soils, it is allowed to use grounding conductors, the resistance of which is determined as

Recognizing the difficulty of producing such a relatively low ground resistance, the standard recommends chemical treatment or partial replacement of the ground. An assessment of the volume of recommended work in specific conditions deserves attention. It's easy to do for the simplest situation, focusing on a hemispherical grounding electrode, the potential of which in a two-layer soil (regardless of what was done - chemistry or mechanical replacement of the soil) according to Fig. 11 is equal

Figure 11. To assess the grounding resistance in two-layer soil

Where exact value ground resistance is defined as

In the extreme case where chemical treatment or soil replacement has proven so effective that it resistivity dropped to almost zero

The expression allows us to estimate the processing radius r 1 from below. In the example under consideration, it turns out to be approximately 40 m, which corresponds to a soil volume of about 134,000 m 3. The obtained value makes us think very seriously about the reality of the planned operation.

Figure 12. Grounding resistance of a two-beam horizontal ground electrode depending on the thickness of the top treated soil layer

An assessment leads to a similar result for any other practically significant configuration of grounding electrodes, for example, for a two-beam grounding system made of horizontal busbars 20 m long. The calculated dependence in Fig. 12 allows us to evaluate how the grounding resistance of such a structure changes with variations in the thickness of the upper low-resistivity layer of the replaced soil. The required grounding resistance of 20 Ohms is obtained here with a thickness of the treated (or replaced) layer of 2.5 m. It is important to understand at what distance from the ground electrode the treatment can be stopped. The indicator is the potential on the earth's surface U(r). A change in resistivity will cease to affect the result where the potential U(r) becomes much less than the potential of the grounding electrode U З = U(r 0).

2.2. For what purpose is a lightning rod grounded?

Please do not consider the section title trivial. Lightning rods have always been grounded since their invention, otherwise how could they conduct lightning current into the ground. Modern manuals say that grounding resistance should be provided safe drainage of lightning current. What danger and safety are we talking about? There is no excuse for this with platitudes. It's probably worth remembering again air lines power transmission There, the grounding resistance determines the resistive component lightning surges which act on a string of insulators.

Lightning rods have nothing like this. Their lightning rod “without problems” accepts the potential of the grounding electrodes. The presence of finite grounding resistance does not in any way affect the ability of the lightning rod to attract lightning. The laboratory has repeatedly tried to monitor 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 to itself by the plasma channel of the counter discharge, which starts from the top of the lightning rod at electric field thundercloud and the charge of 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 at the grounding resistance of the lightning rod is of little significance 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 Ohms, 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 separate lightning rod, as is known, 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 very specific distances from the lightning rod to the object by air and by ground are selected. Let's assume that they are chosen correctly and really exclude spark overlap. Nevertheless, the current enters the object’s grounding electrode and does so in a fairly significant proportion, especially when the function of its grounding is performed by the foundation of the protected structure, which is quite large in area. Calculated data in Fig. 14 show this share depending on the distance between the ground electrodes. At the lightning rod, it is made in accordance with the requirements 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 3 m. Computer calculations were performed for homogeneous soil and for the case when surface layer the main soil to a depth of 2.5 m is replaced by highly conductive soil with a resistivity that is 50 times less. It is easy to verify that the insulation distance of 5 m, prescribed by the Transneft JSC standard, does little to prevent lightning current from penetrating the object through the ground, especially if it upper layer replaced or chemically treated. Even at a distance of 15 m, normalized by the Gazprom OJSC standard, the current in the facility’s ground electrode exceeds 50%.

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

Here it is necessary to emphasize once again that any treatment of the top layer of soil, which reduces the grounding 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 grounding resistance. There remain two untouched aspects of the problem - the formation of spark channels and 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 lightning rod grounding conductor and its grounding resistance. Calculation curves in Fig. Figure 15 demonstrates the dynamics of the step voltage decrease with distance from a typical lightning rod ground electrode, prescribed by Instruction RD 34.21.122-87 (see explanations to 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 value of the grounding resistance of the lightning rod has little effect on the quality of external lightning protection. In any case, it is not directly related to the dangerous effects of lightning that could lead to a catastrophic situation at a tank farm or any other hydrocarbon fuel processing facility. Most importantly, I would really 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 standard design from RD 34.21.122-87 turns out to be quite capable. For example, with the recommended horizontal bus length of 12 m and 3 vertical rods of 5 m each, the grounding resistance in the soil with resistivity ρ is equal to

This means that at ρ ≤ 300 Ohm m the calculated value will not exceed 20 Ohm. With a higher soil resistivity, 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 significantly exceeds 1000 Ohm*m. This is where the organization comes into focus. single contour grounding for all free-standing lightning rods. It is worth turning to Fig. again. 4, which demonstrates the protection of a tank farm by 3 cables 100 m long, with a distance between parallel cables of 50 m. The combination of their supports with horizontal busbars forms a grounding loop with two cells 100x50 m. Its grounding resistance when the busbars are laid to a depth of 0.7 m provides

which makes it possible to solve the problem in soil with a resistivity of up to 3000 Ohm*m, even following the requirements of the Gazprom standard. It is appropriate to note that additional device The local grounding conductor at each of the lightning rods has almost no effect on the grounding resistance of the formed circuit as a whole. Thus, the use of a foundation rack with metal reinforcement 5 m long and an equivalent radius of 0.2 m (R gr ≈ 0.1ρ [Ohm]) in a system of 6 racks as a local grounding conductor for each lightning rod reduced the total resistance of the grounding loop by only 6%. The reason for such a weak influence lies in the effective shielding of the rods by extended horizontal buses. By extending the horizontal busbars connecting the supports of lightning rods, it is possible to achieve a grounding resistance of about 20 Ohms even in soil with a resistivity 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 pulse current due to its inductance. There is nothing to object to this. But at least two circumstances still act in favor of the proposed solution. Firstly, none of the mentioned standards require any specific values ​​of pulsed grounding resistance, and secondly, in high-resistivity soils, the penetration rate of pulsed current into the grounding bus is quite high and therefore present value grounding resistance R gr (t) = U gr (t)/i M (t) quickly takes on a steady value controlled regulatory requirements. As an example in Fig. Figure 16 shows the calculated dynamics of changes in the grounding resistance of a 200 m long bus between the lightning rod supports. It is accepted that the soil resistivity is 5000 Ohm*m, and its relative dielectric constant is 5 (taking this parameter into account is important when capacitive leakage into the soil is comparable to conductive leakage).

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

Useful materials:

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

Modern office and now residential buildings contain many engineering systems life support. It is difficult to imagine the absence of ventilation systems, fire extinguishing systems, video surveillance, access control, etc. Naturally, the designers of such systems have concerns that the “delicate” electronics will fail as a result of lightning. At the same time, some doubts arise among practitioners about the feasibility of connecting the contours of two types of grounding and a desire arises “within the limits of the law” to design electrically unconnected groundings. Is this approach possible and will it actually improve 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 high voltage a breakdown of the gap between the lightning rod and metal structures at home, including electrical cables. The consequence of this will be the emergence of uncontrolled currents, which can lead to fire, failure of electronics and even destruction of infrastructure elements (for example, plastic water pipes). Experienced electricians say: “Give lightning a way, otherwise it will find it on its own.” This is why electrical grounding is mandatory.

For the same reason, the PUE recommends electrically combining not only the groundings located in the same building, but also the groundings of geographically close 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 standards of PUE-7, clause 1.7.55, by connecting grounding conductors electrical conductors in quantities of at least two pieces. Moreover, conductors can be either natural (for example, metal elements building structures) and artificial (wires, rigid tires, etc.).

One common or separate grounding devices?

Grounding conductors for electrical installations and lightning protection require: different requirements, and this circumstance can become a source of some problems. The ground electrode for lightning protection must lead a large electric charge. At the same time, according to the “Lightning Protection Instructions 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, grounding conductors are required, with the exception of category 1 of lightning protection, when three such pins are needed. That is why the most common grounding option for a lightning rod is two or three pins, each about 3 m long, connected by a metal strip buried at least 50 cm into the ground. When using parts produced by ZANDZ, such a ground electrode is durable and easy to install.

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

If the soil parameters and resistance requirements allow for a single grounding in the building for lightning rods and grounding of electrical installations, there are no obstacles to doing it. In other cases, various grounding loops are made for the lightning rod and electrical installations, but they must be connected electrically, preferably in the ground. The exception is the use of some special equipment especially 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 building's potential equalization system through the main grounding bus. And, if such a connection is not provided for in the operating instructions for the equipment, then special measures are taken to prevent people from simultaneously touching the specified equipment and metal parts of the building.

Electrical ground connection

A circuit with several electrically connected grounds ensures that different, sometimes conflicting, requirements for grounding devices are met. According to the PUE, grounding, like many other metal elements of the building, as well as equipment installed in it, must be connected by a potential equalization system. By potential equalization we mean electrical connection conductive parts to achieve equal potential. There are main and additional system potential equalization. Grounding connections are connected to the main potential equalization system, that is, they are connected to each other through the main grounding bus. The wires connecting the grounding 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 safe work of the entire system, it is very important to use as much as possible reliable connection between the groundings and the main grounding bus, which will not be destroyed by lightning. To do this, you need to comply with the standards of PUE and GOST R 50571.5.54-2013 “Low-voltage electrical installations. Part 5-54. Grounding devices protective conductors and protective potential equalization conductors” regarding the cross-section of the potential equalization system wires and their connections to each other.

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

conclusions

The recommendation of the PUE on the electrical connection of all grounding loops in the building is justified and correct implementation not only does it not create a danger for 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 grounding electrode, a separate process grounding can be installed in accordance with the manual supplied with the equipment. The potential equalization system, which combines disparate grounding 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.