Calculation of grounding devices in electrical installations. Online calculation of the grounding loop, calculation of the grounding device, ground electrode. Universal formula for calculating the resistance of a vertical rod

Technical literature often talks about grounding and grounding. Indeed, the issue of grounding in houses and apartments arose in our country relatively recently. Even when communist brigades electrified the country, only phase and neutral were supplied to village houses. They were silent about the grounding wire. Firstly, they saved aluminum as a strategic metal for aircraft, and secondly, few people cared about the problems of protecting the population from electric shock, and thirdly, they did not think about grounding as an effective measure to protect people. Enough time has passed for the communists to disappear, and with them the country they ruled, but the monuments they left behind still stand. Monuments stand, but houses are destroyed.

In our houses, only water supply, sewer and gas pipes, as well as floor panels, are grounded. At the same time, the gas pipeline pipes are not suitable for grounding due to the explosive gas that flies through them. Sewage pipes cannot be used for grounding either. Although the sewer system is entirely made of cast iron, the joints of the cast iron pipes are sealed with cement, which is a poor conductor. Water supply pipes seem to be a good grounding device, but you need to take into account that the pipes are not laid in the ground, but in a layer of insulation in special channels. The most reliable grounding is from the floor distribution board.

At the enterprises, everything was initially done correctly and everything that was possible was grounded. In addition to grounding, enterprises use grounding. Many people mistakenly believe that grounding is the wiring in the socket from the neutral wire to the ground contact. The concepts of “grounding” and “zeroing” are closely related to the concept of neutral.

Neutral is the point where three phases converge through the star-connected windings in a transformer. If this point is connected to grounding conductors, a solidly grounded neutral of the transformer is formed, and the overall system is called grounded. If you weld a bus to this point and connect it to all devices and devices, then the equipment will be grounded.

If the neutral is connected to the neutral bus (without grounding electrodes), then an isolated neutral of the transformer is formed, and the overall system is called neutralized. If this bus is connected to all devices and devices, then the equipment will be zeroed.

The idea is that current flows through a grounded or neutralized conductor only when there is a phase imbalance, but this is for a transformer and during emergency operating conditions. You cannot choose whether to ground or ground the equipment. This has already been done at the substation. Typically a solidly grounded neutral is used.

If, for example, the motor winding of a washing machine is destroyed and resistance appears between the housing and the winding, then there will be a potential on the body of the washing machine that can be detected with an indicator screwdriver. If the machine is not grounded, then when you touch the body, the potential of the machine will become the potential of your hand, and since the bathroom where the machine is located is a particularly dangerous room from the point of view of electric shock and therefore the floor is conductive, the leg will acquire zero potential and this means you will receive a shock with a voltage proportional to the potential of the arm. If the machine is grounded, then in theory the circuit breaker will trip. If the machine is grounded, the potential will spread around the entire machine and upon contact, the potentials of the arm and leg will be the same. You just need to take into account that the current spreads around and when you walk, your legs are under different potentials. And, of course, you can get a stress shock.

Grounding application criteria

Protective grounding is an intentional electrical connection to the ground or its equivalent of metallic non-current-carrying parts of electrical installations that may be energized.

Protective grounding is used in networks with voltages up to 1000 V AC - three-phase three-wire with a solidly grounded neutral; single-phase two-wire, isolated from ground; two-wire DC networks with an isolated midpoint of the current source windings; in networks above 1000 V AC and DC with any neutral mode.

Grounding is mandatory in all electrical installations at voltages of 380 V and above alternating current, 440 V and above direct current, and in rooms with increased danger, especially dangerous and in outdoor installations at voltages of 42 V and above alternating current, 110 V and above direct current; at any voltage in explosive areas.

Depending on the location of the grounding conductors relative to the grounding equipment, two types of grounding devices are distinguished - remote and contour.

With a remote grounding device, the ground electrode is placed outside the site on which the equipment being grounded is located.

With a contour grounding device, the ground electrodes are placed along the contour (perimeter) of the site on which the equipment to be grounded is located, as well as inside this site.

In open electrical installations, the housings are connected directly to the ground electrode by wires. A grounding line is laid in buildings, to which grounding wires are connected. The grounding line is connected to the ground electrode in at least two places.

As grounding conductors, first of all, natural grounding conductors should be used in the form of underground metal communications (with the exception of pipelines for flammable and explosive substances, heating pipes), metal structures of buildings connected to the ground, lead cable sheaths, casing pipes of artesian wells, wells, pits, etc.

As natural grounding conductors of substations and distribution devices, it is recommended to use grounding conductors of the supports of outgoing overhead power lines connected to the grounding device of the substations or distribution device using lightning protection cables of the lines.

If the resistance of natural grounding conductors Rз satisfies the required standards, then the installation of artificial grounding conductors is not required. But this can only be measured. It is impossible to calculate the resistance of natural grounding conductors.

When natural grounding conductors are not available or their use does not produce the desired results, artificial grounding conductors are used - angle steel rods measuring 50X50, 60X60, 75X75 mm with a wall thickness of at least 4 mm, 2.5 - 3 m long; steel pipes with a diameter of 50-60 mm, a length of 2.5 - 3 m with a wall thickness of at least 3.5 mm; rod steel with a diameter of at least 10 mm, length up to 10 m or more.

Grounding conductors are driven in a row or along a contour to a depth at which 0.5 - 0.8 m remains from the upper end of the grounding conductor to the surface of the earth. The distance between vertical grounding conductors must be at least 2.5-3 m.

To connect vertical grounding electrodes to each other, steel strips with a thickness of at least 4 mm and a cross-section of at least 48 sq. mm or a steel wire with a diameter of at least 6 mm are used. The strips (horizontal grounding conductors) are connected to the vertical grounding conductors by welding. The welding area is coated with bitumen for moisture insulation.

Grounding lines inside buildings with electrical installations with voltages up to 1000 V are made with a steel strip with a cross-section of at least 100 sq. mm or round steel of the same conductivity. Branches from the main line to electrical installations are made with a steel strip with a cross-section of at least 24 sq. mm or round steel with a diameter of at least 5 mm.

The standardized resistances of grounding devices are given in Table 1.

Table 1. Permissible resistance of the grounding device in electrical installations up to and above 1000 V

Estimated ground fault currents are taken according to power system data or by calculations. In principle, when building a cottage, ground fault current is not needed. This is a question of grounding the substation.

The calculation of grounding using the utilization coefficient method is carried out as follows.

1. In accordance with the PUE, the required grounding resistance Rз is established according to Table 1.

2. Determine by measurement, calculation or based on data from operating similar grounding devices the possible resistance to spreading of natural grounding conductors Re.

3. If Re Rз, then an artificial grounding device is necessary.

4. Determine the soil resistivity ρ from Table 2. When making calculations, these values ​​should be multiplied by the seasonality coefficient, depending on the climatic zones and the type of ground electrode (Table 3).

Table 2. Approximate values ​​of soil and water resistivities p, Ohm m

Approximate distribution of CIS countries by climatic zones:

1 zone: Arkhangelsk, Kirov, Omsk, Irkutsk regions, Komi, Ural;

Zone 2: Leningrad and Vologda regions, central part of Russia, central regions of Kazakhstan, southern part of Karelia.

Zone 3: Latvia, Estonia, Lithuania, Belarus, southern regions of Kazakhstan; Pskov, Novgorod, Smolensk, Bryansk, Kursk and Rostov regions.

Zone 4: Azerbaijan, Georgia, Armenia, Uzbekistan, Tajikistan, Kyrgyzstan, Turkmenistan (except mountainous areas), Stavropol Territory, Moldova.

Table 3. Signs of climatic zones and values ​​of the coefficient K c

5. Determine the resistance, Ohm, to the spreading of one vertical ground electrode - a round rod (tubular or angular) in the ground:

Table 4. Usage coefficients M in vertical electrodes made of pipes, angles or rods placed in a row without taking into account the influence of the communication band

Table 5. MV utilization coefficients of vertical electrodes made of pipes, angles or rods placed along the contour without taking into account the influence of the communication band

6. When constructing simple grounding conductors in the form of a short row of vertical rods, the calculation can be completed at this point and the conductivity of the connecting strip cannot be determined, since its length is relatively short (in this case, the actual resistance of the grounding device will be somewhat overestimated). As a result, the general formula for calculating the resistance of vertical grounding conductors looks like this:

p - Approximate values ​​of soil and water resistivity, Ohm m, table 2

KS - Characteristics of climatic zones and coefficient values, table 3.

L – length of vertical ground electrode, m

d – diameter of vertical ground electrode, m

t’ – length from the ground surface to the middle of the vertical ground electrode, m

Mv is the coefficient of use of vertical grounding electrodes, depending on the number of grounding electrodes and the distance between them (Tables 4, 5). The preliminary number of vertical grounding conductors for determining Mv can be taken equal to Mv = rv/Rz

a – the distance between vertical grounding conductors (usually the ratio of the distance between vertical grounding conductors to their length is taken equal to a/l=1;2;3)

in this case l>d, t0>0.5 m;

for a corner with flange width b, d=0.95b is obtained.

For horizontal grounding conductors calculation is carried out using the same utilization factor method

1. Determine the resistance, Ohm, to the spreading of the horizontal ground electrode. For round rod section:

Table 6. Usage coefficients M g of a horizontal strip electrode (pipes, angles, strips, etc.) when placing vertical electrodes in a row.

Table 7. Usage factor M g of a horizontal strip electrode (pipes, angles, strips, etc.) when placing vertical electrodes along the contour.

p - approximate values ​​of soil and water resistivity, Ohm m, table 2

KS - characteristics of climatic zones and coefficient values, table 3.

L – length of horizontal ground electrode, m

d – diameter of the horizontal grounding conductor, m

t’ – length from the ground surface to the middle of the horizontal ground electrode, m

MV is the coefficient of use of horizontal grounding conductors, depending on the number of grounding conductors and the distance between them (Tables 6, 7).

a – the distance between horizontal grounding conductors (usually the ratio of the distance between horizontal grounding conductors to their length is taken equal to a/l=1;2;3)

Rз - Permissible resistance of the grounding device in electrical installations up to and above 1000 V, table 1

Here l>d, l>>4t’. For a strip of width b, d=0.5b is obtained.

Example 1

Calculate the grounding device of a 35/10 kV factory substation located in the second climatic zone. 35 and 10 kV networks operate with an ungrounded neutral. On the 35 kV side Iz=8A, on the 10 kV side Iz=19A. The substation's own needs are powered by a 10/0.4 kV transformer with a grounded neutral on the 0.4 kV side; there are no natural grounding conductors. Specific soil resistivity at normal humidity p=62 Ohm*m. The electrical equipment of the substation occupies an area of ​​18*8 sq.m.

Solution

Let's estimate the number of vertical electrodes to be 10 pcs. according to table 5, Mv=0.58.

If Nв<10, все хорошо и можно принимать Nв=9 электродов.

If Nв>10, it is necessary to increase МВ, which will accordingly increase the approximate number of electrodes.

Let's estimate the number of horizontal electrodes to be 50 pcs. according to table 6, Mg=0.2.

If Ng<50, все хорошо и можно принимать Nг=49 электродов.

If Ng>50, then it is necessary to increase Mv, which will accordingly increase the approximate number of electrodes.

Example 2

Calculate the grounding device for a cottage in Belarus. The cottage stands on clay soil, therefore the soil resistivity is p=40 Ohm*m. For grounding, fittings with a diameter of 12 mm and a length of 2 meters are used.

Solution

According to table 1 – Rз=4

According to table 2 – p=40 Ohm*m

According to table 3 – Kc=1.6

The electrodes will be placed in a row, so using Table 4 we will estimate the number of vertical electrodes, for example 10 pcs. Mv=0.62
The driving depth of all electrodes from the surface of the earth is 0.7 meters, plus half the length of a two-meter electrode and therefore t’=1.7 meters.

Find the number of vertical electrodes

If Nв>10, then it is necessary to increase МВ, which will accordingly increase the approximate number of electrodes.

Using Table 4, we estimate the number of vertical electrodes, a total of 15 pieces. Mv=0.56

If Nв<15, все хорошо и можно принимать Nв=14 электродов.

Let's go the other way and weld a frame from pins, burying it 0.8 meters underground. This is how horizontal grounding conductors are obtained.

According to table 1 – Rз=4

According to table 2 – p=40 Ohm*m

According to table 3 – Kc=1.6

The driving depth of all electrodes from the surface of the earth is 0.7 meters, plus half the length of a two-meter electrode and therefore t’=1.7 meters

Let's estimate the number of horizontal electrodes, for example 30 pcs. according to table 6, Mg=0.24

If Ng>30, then it is necessary to increase Mg, which will accordingly increase the approximate number of electrodes.

Using Table 6, let’s estimate the number of horizontal electrodes, for example 50 pcs. Mg=0.21

If Ng<10, все хорошо и можно принимать Nг=37 электродов.

Grounding takes into account the Earth's ability to conduct electricity. Grounding electrodes are usually made of steel. Over time, steel rusts and breaks down, and the grounding is lost. This process is irreversible, but zinc coated steel rods can be used. Zinc is also a metal, but it is not susceptible to rust as long as there is a layer of zinc. When zinc is washed out over time or worn away by mechanical means, for example, when driving electrodes into hard soil, stones can peel off the coating, then the corrosion rate will double. Sometimes special electrodes coated with copper are used.

Grounding rods can be taken from those that were used as reinforcement for the concrete foundation. They cannot be painted or coated with resinous compounds - the resin will act as an insulator and there will be no grounding at all. The longer the rods, the fewer of them will be needed for grounding, but the more difficult it is to drive them into the soil. Therefore, first you need to dig a trench 1 meter deep. Hammer a piece of pre-sharpened reinforcement into the trench so that it protrudes no more than 20 centimeters from the bottom of the trench. Then, after 2 meters, the next reinforcement is driven in, and so on according to calculation. Next, reinforcement is placed at the bottom of the trench and welded to all the driven pins. The welding area must be coated with bitumen for moisture insulation. This is done because reinforcement 12 millimeters thick will rot in the ground for a very long time, but the welding site is relatively small in area, but the most important.

After driving all the electrodes, you can conduct the experiment. We pull the extension cord out of the house. The voltage source must come from a pole from the substation. You cannot use an autonomous source such as a generator for testing - there will be no closed circuit. We find a phase on the extension cord and connect one wire from the light bulb, and with the second wire we touch the scalded electrodes. If the light bulb is lit, then we measure the voltage between the phase wire and the grounded electrodes, the voltage should be 220 V, but the light bulb should glow quite brightly. You can also measure the current through a 100 W light bulb. If the current is approximately 0.45 A, everything is fine, but if the current is much less, you should add ground rods.

It is necessary to achieve the normal glow of the light bulb and the current within normal limits. After this, the welding areas are filled with bitumen and a piece of reinforcement is removed from the trench, attaching it to the house. After this, the trench can be backfilled. The removed piece of reinforcement must be welded to the electrical distribution board in the cottage. Disconnect all points from the shield with copper cables.

We continue to review the best software for electricians, and in this article I would like to focus on a review of programs for calculating grounding. Before moving to or at a substation, the first thing you need to do is calculate the protective grounding resistance, as well as the number of electrodes and the length of the horizontal ground electrode. In addition, calculated data regarding the cross-section of the main shield, the main PE conductor, and even the calculation of the step voltage will be useful. All this can be done using special programs, which we will talk about now.

"Electrician"

The first software product that I would like to consider is called “Electric”. We already talked about it when we looked at the best ones. So, “Electrician” can easily cope with calculations of the parameters of the grounding loop. The advantage of this product is that it is quite easy to use, it is Russified, and it is also possible to download for free. You can see the program interface in the screenshots below:

All you need is to set the initial data, and then click the “Calculate Contour” button. As a result, you will receive not only a detailed calculation method with the formulas used, but also a drawing that will show the finished ground loop. As for the accuracy of calculation work, we recommend using only the latest versions of the program, because There are many bugs in outdated versions that have been eliminated over time. If you need to calculate the grounding loop for a private house or more serious structures, for example, a boiler room or substation, we recommend using this product.

The calculation of grounding in the Electrician program is shown in the video:

"Calculation of grounding devices"

The name of the second program speaks for itself. Thanks to it, it is possible to calculate not only the grounding loop, but also lightning protection, which is also extremely necessary. The program interface is quite simple, in fact, as in the analogue discussed above. The form for filling out the initial data looks like this:

If you need to perform a simple calculation of the grounding loop right now, you can use ours. The accuracy of the calculations is, of course, inferior to the software products provided in the article, but you will still get approximate values, which are worth focusing on.

"Grounding"

Another software product whose name speaks for itself. As in the previous two programs, you can figure it out without any problems, because The interface is simple and presented in Russian. The latest version of the program (v3.2) allows not only to calculate the reserve, but also to evaluate the possibility of using reinforced concrete foundations of industrial buildings as a protective contour. In addition, the program can help you select the cross-section of the main shield, PE conductor, as well as conductors of the potential equalization system. Another useful functionality of the product is the calculation of touch voltage and . You have already seen the interface a little higher, it looks like this:

The fact is that the creators of this program are also the creators of Electric, so you can download one of the products provided in the range.

"ElectriCS Storm"

A more complex program to use that requires modeling skills is ElectriCS Storm. It is not advisable to use it to calculate the grounding loop of a house, because you will most likely get confused and calculate everything with errors. We recommend that energy professionals or university students with overlapping specialties work with this software.

The advantage of this software product is that it is possible to design a grounding device (GD) and thereby display a 3D model of finished protective circuits. In addition, the functionality of the program allows you to calculate the electromagnetic environment and grounding of substations.

All drawings can be saved in dwg format, so they can later be opened in AutoCAD.

Well, our list of the best programs for calculating grounding is completed by the power engineering software package called “Shark”, thanks to which you can count on:

• grounding devices;
• lightning protection;
• characteristics of protective devices;
• voltage loss up to 1 kV;
• power of facilities, as well as electric boilers and air conditioners;
• wiring section;

The interface is also intuitive and presented in Russian:

“Shark” is available for free download, so finding it on the Internet will not be difficult. Finally, we recommend watching a very useful video

The most important function of grounding is electrical safety. Before installing it in a private house, at a substation and in other places, it is necessary to carry out a grounding calculation.

What does grounding of a private house look like?

Electrical contact with the ground is created by a metal structure of electrodes immersed in the ground along with connected wires - all of this is a grounding device (GD).

The points where the conductor, protective conductor or cable shield connects to the charger are called grounding points. The figure below shows grounding from one vertical metal conductor 2500 mm long, buried in the ground. Its upper part is placed at a depth of 750 mm in a trench, the width of which at the bottom is 500 mm and at the top – 800 mm. The conductor can be connected by welding to other similar grounding conductors in a circuit with horizontal plates.

Type of the simplest grounding of a room

After installing the ground electrode, the trench is filled with soil, and one of the electrodes should go outside. A wire above the ground is connected to it, which goes to the ground bus in the electrical control panel.

When the equipment is in normal conditions, the voltage at the grounding points will be zero. Ideally, during a short circuit, the resistance of the charger will be zero.

When a potential occurs at a grounded point, it must be reset to zero. If we consider any calculation example, we can see that the short circuit current Is has a certain value and cannot be infinitely large. The soil has a resistance to current spreading R from points with zero potential to the ground electrode:

R z = U z / I z, where U z is the voltage on the ground electrode.

Solving the problem of correct grounding calculation is especially important for a power plant or substation where a lot of equipment operating under high voltage is concentrated.

MagnitudeRhdetermined by the characteristics of the surrounding soil: humidity, density, salt content. Here, important parameters are also the design of the grounding conductors, the immersion depth and the diameter of the connected wire, which must be the same as that of the electrical wiring cores. The minimum cross-section of bare copper wire is 4 mm 2, and that of insulated copper wire is 1.5 mm 2.

If a phase wire touches the body of an electrical appliance, the voltage drop across it is determined by the values ​​of Rz and the maximum possible current. The touch voltage U pr will always be less than U z, since it is reduced by a person’s shoes and clothing, as well as by the distance to the grounding conductors.

On the surface of the earth, where the current spreads, there is also a potential difference. If it is high, a person may come under step voltage U sh, which is life-threatening. The farther from the grounding conductors, the smaller it is.

The value of U s must have an acceptable value to ensure human safety.

The values ​​of Upr and Uw can be reduced if Rz is reduced, due to which the current flowing through the human body will also decrease.

If the voltage of an electrical installation exceeds 1 kV (for example, substations at industrial enterprises), an underground structure is created from a closed circuit in the form of rows of metal rods driven into the ground and connected by welding to each other using steel strips. Due to this, potentials are equalized between adjacent points on the surface.

Safe work with electrical networks is ensured not only by the presence of grounding of electrical appliances. For this you also need fuses, circuit breakers and RCDs.

Grounding not only ensures the potential difference to a safe level, but also creates a leakage current, which must be sufficient to trigger the protective equipment.

It is impractical to connect every electrical appliance to a ground electrode. Connections are made through a bus located in the apartment panel. The input for it is a grounding wire or a PE wire laid from the substation to the consumer, for example, through the TN-S system.

Calculation of the grounding device

The calculation consists of determining R z. To do this, you need to know the soil resistivity ρ, measured in Ohm*m. The basis is taken as its average values, which are tabulated.

Determination of soil resistivity

From the values ​​given in the table it can be seen that the value of ρ depends not only on the composition of the soil, but also on humidity.

In addition, the tabulated resistivity values ​​are multiplied by the seasonality coefficient K m, which takes into account soil freezing. Depending on the lowest temperature (0 C), its values ​​can be as follows:

• from 0 to +5 – K m =1.3/1.8;
• from -10 to 0 – K m =1.5/2.3;
• from -15 to -10 – K m =1.7/4.0;
• from -20 to -15 – K m =1.9/5.8.

The values ​​of the coefficient K m depend on the method of laying the grounding conductors. The numerator shows its values ​​for vertical immersion of ground electrodes (with the tops placed at a depth of 0.5-0.7 m), and the denominator for a horizontal arrangement (at a depth of 0.3-0.8 m).

In a selected area, soil ρ may differ significantly from the average table values ​​due to man-made or natural factors.

When approximate calculations are carried out, for a single vertical ground electrode R z ≈ 0.3∙ρ∙ K m.

An accurate calculation of protective grounding is made using the formula:

R з = ρ/2πl∙ (ln(2l/d)+0.5ln((4h+l)/(4h-l)), Where:

• l – electrode length;
• d – rod diameter;
• h – depth of the midpoint of the grounding conductors.

For n vertical electrodes connected from above by welding R n = R з /(n∙ K used), where K used is the electrode utilization factor, taking into account the shielding effect of neighboring ones (determined from the table).

Location of ground electrodes

There are many formulas for calculating grounding. It is advisable to apply the method for artificial grounding conductors with geometric characteristics in accordance with the PUE. The supply voltage is 380 V for a three-phase current source or 220 V single-phase.

The normalized resistance of the ground electrode, which should be guided by, is no more than 30 Ohms for private houses, 4 Ohms for a current source at a voltage of 380 V, and for a 110 kV substation - 0.5 Ohms.

For a group charger, a hot-rolled angle with a flange of at least 50 mm is selected. A strip with a cross section of 40x4 mm is used as horizontal connecting jumpers.

Having decided on the composition of the soil, its resistivity is selected from the table. In accordance with the region, an increasing seasonality factor K m is selected.

The number and method of arrangement of charger electrodes are selected. They can be installed in a row or in a closed loop.

Closed ground loop in a private house

In this case, their shielding influence on each other occurs. The closer the ground electrodes are located, the greater the value. The values ​​of the utilization coefficients of grounding electrodes K used for a circuit or located in a row are different.

Coefficient valuesKispat different electrode locations

The influence of horizontal bridges is insignificant and may not be taken into account in evaluation calculations.

Examples of ground loop calculations

To better master the methods of calculating grounding, it is better to consider an example, or better yet, several.

Example 1

Grounding electrodes are often made by hand from a steel angle 50x50 mm 2.5 m long. The distance between them is chosen equal to the length - h = 2.5 m. For clay soil ρ = 60 Ohm∙m. The seasonality coefficient for the middle zone, selected from the tables, is 1.45. Taking this into account, ρ = 60∙1.45 = 87 Ohm∙m.

For grounding, a trench 0.5 m deep is dug along the contour and a corner is hammered into the bottom.

The size of the angle flange is reduced to the nominal diameter of the electrode:

d = 0.95∙p = 0.995∙0.05 = 87 Ohm∙m.

The depth of the midpoint of the corner will be:

h = 0.5l+t = 0.5∙2.5+0.5 = 1.75 m.

By substituting the values ​​into the previously given formula, you can determine the resistance of one ground electrode: R = 27.58 Ohm.

According to the approximate formula R = 0.3∙87 = 26.1 Ohm. From the calculation it follows that one rod will clearly not be enough, since according to the requirements of the PUE, the value of the normalized resistance is R norm = 4 Ohms (for a network voltage of 220 V).

The number of electrodes is determined by the approximation method using the formula:

n = R 1 /(k used R norms) = 27.58/(1∙4) = 7 pcs.

Here, k isp = 1 is first assumed. Using the tables, we find for 7 grounding switches k isp = 0.59. If we substitute this value into the previous formula and recalculate again, we get the number of electrodes n = 12 pcs. Then a new recalculation is made for 12 electrodes, where again, according to the table, k isp = 0.54. Substituting this value into the same formula, we get n = 13.

Thus, for 13 corners R n = R z /(n*η) = 27.58/(13∙0.53) = 4 Ohm.

Example 2

It is necessary to make artificial grounding with a resistance R norm = 4 Ohms, if ρ = 110 Ohm∙m.

The ground electrode is made of rods with a diameter of 12 mm and a length of 5 m. The seasonality coefficient according to the table is 1.35. You can also take into account the condition of the soil k. Measurements of its resistance were carried out during the dry period. Therefore, the coefficient was k g =0.95.

Based on the data obtained, the following value is taken as the calculated value of earth resistivity:

ρ = 1.35∙0.95∙110 = 141 Ohm∙m.

For a single rod R = ρ/l = 141/5 = 28.2 ohms.

The electrodes are arranged in a row. The distance between them should be no less than the length. Then the utilization rate will be according to the tables: ksp = 0.56.

Find the number of rods to obtainRnormal= 4 ohms:

n = R 1 /(k used R norms) = 28.2/(0.56∙4) = 12 pcs.

After grounding is installed, electrical parameters are measured on site. If the actual R value is higher, more electrodes are added.

If natural grounding electrodes are nearby, they can be used.

This is especially often done at the substation where the lowest R value is required. The equipment here is used to the maximum: underground pipelines, power line supports, etc. If this is not enough, artificial grounding is added.

Independent grounding calculations are estimates. After its installation, additional electrical measurements should be made, for which specialists are invited. If the soil is dry, you need to use long electrodes due to poor conductivity. In wet soil, the cross-section of the electrodes should be taken as large as possible due to increased corrosion.

) for a single deep ground electrode based on modular grounding is carried out as a calculation of a conventional vertical ground electrode made of a metal rod with a diameter of 14.2 mm.

Formula for calculating the grounding resistance of a single vertical ground electrode:

Where:
ρ - soil resistivity (Ohm*m)
L - length of the ground electrode (m)
d - diameter of the ground electrode (m)
T - depth of the ground electrode (distance from the surface of the earth to the middle of the ground electrode)(m)
π - mathematical constant Pi (3.141592)
ln - natural logarithm

For ZANDZ electrolytic grounding, the formula for calculating grounding resistance is simplified to the form:

- for set ZZ-100-102

The contribution of the connecting ground conductor is not taken into account here.

Distance between ground electrodes

With a multi-electrode configuration of the grounding electrode, another factor begins to influence the final grounding resistance - the distance between the grounding electrodes. In the grounding calculation formulas, this factor is described by the value “utilization factor”.

For modular and electrolytic grounding, this coefficient can be neglected (i.e. its value is equal to 1) subject to a certain distance between the grounding electrodes:

• not less than the depth of immersion of electrodes - for modular
• not less than 7 meters - for electrolytic

Connecting electrodes to a ground electrode

To connect the grounding electrodes to each other and to the object, copper rod or steel strip is used as a grounding conductor.

The conductor cross-section is often chosen - 50 mm² for copper and 150 mm² for steel. It is common to use ordinary steel strip 5*30 mm.

For a private house without lightning rods, a copper wire with a cross section of 16-25 mm² is sufficient.

More information about laying the grounding conductor can be found on the separate page "Installation of grounding".

Service for calculating the probability of a lightning strike on an object

If, in addition to the grounding device, you have to install an external lightning protection system, you can use a unique one protected by lightning rods. The service was developed by the ZANDZ team together with JSC Energy Institute named after G.M. Krzhizhanovsky (JSC ENIN)

This tool allows you not only to check the reliability of the lightning protection system, but also to carry out the most rational and correct lightning protection design, providing:

• lower cost of design and installation work, reducing unnecessary stock and using smaller lightning rods that are less expensive to install;
• fewer lightning strikes into the system, reducing secondary negative consequences, which is especially important in facilities with many electronic devices (the number of lightning strikes decreases with decreasing height of lightning rods).

• the probability of a lightning breakthrough into system objects (the reliability of the protection system is defined as 1 minus the probability value);
• number of lightning strikes into the system per year;
• number of lightning breakthroughs bypassing protection per year.

Having such information, the designer can compare the customer's requirements and regulatory documentation with the obtained reliability and take measures to change the lightning protection design.

In order to begin the calculation, .

Grounding is a valuable structure that protects owners of home appliances from direct contact with a very useful, but extremely zealous flow of electricity. The grounding device will ensure safety when the zero “burns out,” which often happens on suburban power lines during heavy winds. It will eliminate the risk of injury due to leaks to non-current-carrying metal parts and the housing due to leaky insulation. The construction of a protective system is an event that does not require excessive effort and super investments, if the grounding calculation is done correctly. Thanks to preliminary calculations, the future performer will be able to determine the upcoming expenses and the feasibility of the upcoming task.

To build or not to build?

In the already fairly forgotten time of a meager number of household electrical appliances, owners of private houses rarely “dabbled” with a grounding device. It was believed that natural ground electrodes, such as:

• steel or cast iron pipelines, if insulation is not laid around them, i.e. there is direct close contact with the soil;
• steel casing of a water well;
• metal supports for fences and lanterns;
• lead braided underground cable networks;
• reinforcement of foundations, columns, trusses buried below the seasonal freezing horizon.

Please note that the aluminum sheath of underground cable communications cannot be used as a grounding element, because covered with an anti-corrosion layer. The protective coating prevents current dissipation in the ground.

A steel water supply system laid without insulation is recognized as the optimal natural grounding conductor. Due to its considerable length, the resistance to spreading current is minimized. In addition, the external water supply is laid below the seasonal freezing level. This means that the resistance parameters will not be affected by frost and dry summer weather. During these periods, soil moisture decreases and, as a result, resistance increases.

The steel frame of underground reinforced concrete structures can serve as an element of the grounding system if:

• an area sufficient in accordance with PUE standards is in contact with clayey, loamy, sandy loam and wet sandy soil;
• during the construction of the foundation, the reinforcement in two or more places was exposed to the surface;
• the steel elements of this natural grounding were connected to each other by welding, and not by wire bonding;
• the resistance of the fittings playing the role of electrodes is calculated in accordance with the requirements of the PUE;
• an electrical connection has been established with the grounding bus.

Without meeting the above conditions, underground reinforced concrete structures will not be able to perform the function of reliable grounding.

Of the entire set of natural grounding systems listed above, only underground reinforced concrete structures are subject to calculations. It is not possible to accurately calculate the current spreading resistance of pipelines, metal armor and channels of underground power networks. Especially if they were laid a couple of decades ago, and the surface is significantly corroded.

The effectiveness of natural ground electrodes is determined by banal measurements, for which you need to call an employee of the local energy service. The readings from his device will tell you whether or not the owner of a country property needs a re-grounding loop as an addition to the existing grounding measures carried out by the electricity supply company.

If there are natural grounding conductors on the site with resistance values ​​corresponding to the PUE standards, it is not advisable to arrange protective grounding. Those. if the energy management “agent” device shows less than 4 ohms, the organization of the ground loop can be postponed “for later”. However, it is better to play it safe and prevent possible risks, which is why an artificial grounding device is constructed.

Calculations for an artificial grounding device

It must be admitted that it is difficult, almost impossible, to thoroughly calculate the grounding device. Even among professional electricians, the method of approximate selection of the number of electrodes and the distances between them is practiced. Too many natural factors influence the result of work. The humidity level is unstable, the actual density and resistivity of the soil, etc. are often not thoroughly studied. Because of which, ultimately, the resistance of the constructed circuit or a single ground electrode differs from the calculated value.

This difference is detected using the same measurements and corrected by installing additional electrodes or by increasing the length of a single rod. However, you should not refuse preliminary calculations, because they will help:

• eliminate or reduce additional costs for purchasing material and digging branch trenches;
• select the optimal configuration of the grounding system;
• draw up an action plan.

To facilitate complex and rather confusing calculations, several programs have been developed, but in order to use them correctly, knowledge about the principle and procedure of calculations will be useful.

Components of the protective system

The protective grounding system is a complex of electrodes buried in the ground, electrically connected to a grounding bus. Its main components are:

• one or more metal rods that transmit a spreading current to the ground. Most often, they are used as long pieces of rolled metal vertically driven into the ground: pipes, equal-flange angles, round steel. Less commonly, the function of electrodes is performed by pipes or sheet steel buried horizontally in a trench;
• a metal connection connecting a group of grounding conductors into a functional system. Often this is a horizontally located grounding conductor made of strip, angle or rod. It is welded to the tops of electrodes buried in the ground;
• a conductor connecting a grounding device located in the ground to a bus, and through it to the protected equipment.

The last two components have a common name - “grounding conductor” and, in fact, perform the same function. The difference is that the metal connection between the electrodes is located in the ground, and the conductor connecting the ground to the bus is located on the surface. Hence the different requirements for materials and corrosion resistance, as well as the variation in their cost.

Principles and rules of calculations

A set of electrodes and conductors, called grounding, is installed in the ground, which is a direct component of the system. Therefore, its characteristics are directly involved in the calculations along with the selection of the length of the artificial grounding elements.

The calculation algorithm is simple. They are produced according to the formulas available in the PUE, in which there are variable units that depend on the decision of the independent master, and constant tabular values. For example, the approximate value of soil resistance.

Determining the optimal contour

A competent calculation of protective grounding begins with the selection of a contour that can repeat any of the geometric shapes or a regular line. This choice depends on the shape and size of the site available to the master. It is more convenient and easier to build a linear system, because to install the electrodes you only need to dig one straight trench. But electrodes located in one row will shield, which will inevitably affect the spreading current. Therefore, when calculating linear grounding, a correction factor is introduced into the formulas.

The triangle is considered the most popular pattern for DIY. The electrodes located at the tops of it, at a sufficient distance from each other, do not prevent the current received by each of them from freely dissipating in the ground. Three metal rods for protecting a private home are considered quite sufficient. The main thing is to position them correctly: drive metal rods of the required length into the ground at a distance that is effective for work.

The distances between the vertical electrodes must be equal, regardless of the configuration of the grounding system. The distance between two adjacent rods should not be equal to their length.

Selection and calculation of parameters of electrodes and conductors

The main working elements of protective grounding are vertical electrodes, because they will have to dissipate current leakages. The length of the metal rods is interesting, both from the point of view of the effectiveness of the protective system, and from the point of view of the metal consumption and price of the material. The distance between them determines the length of the metallic bond components: again, the consumption of material to create the grounding conductors.

Please note that the resistance of vertical ground electrodes depends mainly on their length. Transverse dimensions do not significantly affect efficiency. However, the cross-sectional value is standardized by the PUE due to the need to create a wear-resistant protective system, the elements of which will gradually be destroyed by corrosion for at least 5-10 years.

We choose the optimal parameters, taking into account that we don’t need any extra expenses. Don’t forget that the more meters of rolled metal we drive into the ground, the more benefit we will get from the circuit. You can “gain” meters either by increasing the length of the rods or by increasing their number. Dilemma: installing multiple grounding electrodes will force you to work hard as a digger, and hammering long electrodes with a sledgehammer by hand will turn you into a strong hammer hammer.

Which is better: number or length, will be chosen by the direct executor, but there are rules according to which it is determined:

• the length of the electrodes, because they need to be buried below the seasonal freezing horizon by at least half a meter. So it is necessary that the performance of the system does not suffer too much from seasonal factors, as well as from droughts and rains;
• distance between vertical grounding conductors. It depends on the configuration of the circuit and the length of the electrodes. It can be determined using tables.

It is difficult and inconvenient to drive 2.5-3 meter pieces of rolled metal into the ground with a sledgehammer, even taking into account the fact that 70 cm of them will be immersed in a pre-dug trench. The rational length of ground electrodes is considered to be 2.0 m, with variations around this figure. Do not forget that long sections of rolled metal are not easy and will be very expensive to deliver to the site.

We save money wisely on materials

It has already been mentioned that little depends on the cross-section of rolled metal except the price of the material. It makes more sense to buy material with the smallest possible cross-sectional area. Without lengthy discussions, we present the most economical and sledgehammer-resistant options:

• pipes with an internal diameter of 32 mm and a wall thickness of 3 mm or more;
• equal angle corner with a side of 50 or 60 mm and a thickness of 4-5 mm;
• round steel with a diameter of 12-16 mm.

To create an underground metal connection, a steel strip 4 mm thick or a 6 mm rod is best suited. Do not forget that the horizontal conductors need to be welded to the tops of the electrodes, so we will add another 20 cm to the distance between the rods we have chosen. The above-ground section of the grounding conductor can be made from a 4 mm steel strip with a width of 12 mm. You can bring it to the shield from the nearest electrode: this way you will have to dig less, and we will save material.

And now the formulas themselves

We have decided on the shape of the outline and the sizes of the elements. Now you can enter the required parameters into a special program for electricians or use the formulas below. In accordance with the type of grounding conductors, we select a formula for calculations:

Or let’s use the universal formula to calculate the resistance of one vertical rod:

For calculations, you will need auxiliary tables with approximate values, depending on the composition of the soil, its average density, ability to retain moisture and the climatic zone:

Let's calculate the number of electrodes without taking into account the resistance value of the grounding horizontal conductor:

Let's calculate the parameters of the horizontal element of the grounding system - the horizontal conductor:

Let's calculate the resistance of the vertical electrode taking into account the resistance value of the horizontal ground electrode:

According to the results obtained as a result of diligent calculations, we stock up on material and plan the time for the grounding device.

Due to the fact that our protective grounding will have the greatest resistance during dry and frosty periods, it is advisable to begin its construction at this time. If properly organized, it will take a couple of days to build the circuit. Before filling the trench, you will need to check the functionality of the system. This is best done when the soil contains the least amount of moisture. True, winter is not very conducive to working in open areas, and excavation work is complicated by frozen soil. This means that we will start building the grounding system in July or early August.