Types of grounding electrodes. Ring ground electrode. Vertical ground electrodes

The best, cheapest, and least labor intensive type of ground electrode is the base ground electrode. When properly manufactured, it has an almost unlimited service life, and its stability is practically independent of weather conditions. The fundamental grounding electrode provides a high level of protection and safety for the use of electrical equipment, and also does not affect the mechanical strength of building structures. Why is this so rare? The answer is simple. Architects and designers don't care much about this; it's not their industry. That's why they don't invest it in construction projects. Then the only way out is to create a grounding electrode with the hands of electrical installation specialists and connect it to the main electrical network of the new house.

Building ground electrode

The main purpose of grounding a construction site is to comply with the requirements for protection against electric shock when using electrical installations, as well as the functional requirements for installing lightning protection. In particular, these are tasks such as:

• ensuring reliable operation of the electrical installation;
• compliance with all requirements relating to the protection of human life;
• effective equalization of potentials of all objects and removal of overvoltage energy arising in electrical networks, including due to the impact of nearby lightning discharges;
• leading ground fault currents and leakage currents;
• safe dissipation of lightning current discharged from the lightning protection system in the ground.

The design principles of grounding electrodes for lightning protection purposes were included in the GOST R 57190-2016 standard, which distinguishes between two types of grounding electrodes:

• A system of types consisting of horizontal and vertical grounding electrodes made externally. The number of such grounding electrodes must be at least 2
• Type B system, in the form of a base, ring or grid ground electrode.

The effectiveness of a grounding system is determined by its grounding resistance. In general, unless there are special circumstances, the recommendation for normal construction work should not exceed 10 ohms (ohms). However, for single-family homes this is often too restrictive. Sometimes energy companies require this, but this has no basis in legal provisions or technical standards. Private houses are objects with the lowest levels of protection (III and IV), for which the GOST R 57190-2016 standard does not provide the required maximum grounding resistance. Instead, he accepts as acceptable a constant minimum grounding size of 5 m. So whatever grounding resistance comes to us then, that will be accepted.

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Installation of a grounding device (GD)

A grounding device or grounding device (grounding) is a design of electrically interconnected metal or bimetallic conductors of various geometries and configurations, on the one hand, and a volumetric conductor of an infinitely large cross-section of the Earth, on the other.

The purpose and meaning of organizing a grounding (circuit) is to divert the overwhelming majority of the current into the ground in a way that is safe for humans in the event of an electrical installation failure, thereby providing protection from damage to humans and sensitive equipment.

Grounding metal conductors are usually divided into surface (horizontal; strip steel) and deep (vertical; angle, pipe (including casing), circle, fittings) grounding conductors; in some cases, reinforced concrete foundations of buildings/structures are used as a grounding device. Moreover, if the installation depth (buried) of the grounding electrodes is small (3 - 5 meters), then such grounding is also called surface grounding. A deep (underground) grounding device involves deeper mechanical penetration using vibration driving or borehole drilling.

The choice of the final design of the grounding device depends on the power of the electric current that must be safely drained/drained into the ground and the electrochemical characteristics of the soil/earth.

Installation of a grounding device

Grounding installation is usually divided into 4 stages:

• Initial excavation work: digging, drilling.
• Installation work: laying horizontal strips, driving/installing vertical grounding conductors; welding/bolting of grounding device elements; painting the external elements of the grounding device and places of welded joints with a black protective bitumen composition.
• Final excavation work: backfill.
• Measuring work: measuring the resistance of the grounding device.

Initial excavation work

Initial excavation work

Before starting excavation work, it is necessary to mark/mark the route for laying the horizontal ground electrode. For this purpose, it is enough to selectively remove the surface part of the soil to the depth of half a shovel (you can limit yourself to marks in the form of a pit at a distance of half a meter to a meter from each other along the entire length of the route).

full trench

Next, a full-fledged trench is made with a shovel width of 210-240 millimeters and a depth of at least 0.5 meters (ideally: 0.5÷0.7 meters).

When installing deep/underground electrodes (depth up to 200 meters), downhole auger drilling is used using a hole drill or a drilling rig. Drilling is carried out to the designed depth and diameter in a safe manner.

Installation work

Installation work

After completing the initial excavation work, the vertical grounding conductors are driven in/pressed in manually (with a sledgehammer) or mechanically (with an excavator bucket (up to 5 meters), or with a vibrating hammer/perforator with an impact force of 19-21 Joule (up to 30 meters)).

Installation of vertical grounding conductors manually (with a sledgehammer) has a number of limitations:

— Installation depth is no more than 2.5 meters (in practice, the average installation depth is 1.5 meters; the corner bends; the striking point of the corner opens with a “rose”).

— Hard soil (for example, blue clay; stones/boulders, etc.).

— Sandy and frozen soil (high soil resistivity).

The method of pressing a ground electrode into the ground is good to a depth of up to 5 meters and has the same limitations as the manual method.

For the installation of deep-modular (typical deep) grounding conductors, a special SDS-max nozzle is used; For installation of corners or fittings, a professional attachment of our own production for a vibratory hammer or SDS-max is used. This measure significantly simplifies and speeds up the installation process of vertical grounding conductors. Obvious limitations of this method: rocky soil. An obvious advantage: minimal land allocation and season-independent grounding parameters, as well as good results in sandy, high-resistivity soil.

As a rule, strip black or galvanized steel 40x4 mm is used as a vertical grounding conductor. Typically, this strip is supplied in 6-meter long strips or 50-meter coils.

Arc welding

The connection of the strip steel between itself and the vertical electrode is performed using arc welding. After cooling and cleaning off the slag + flux, the welded joint must be coated with a black protective bitumen compound.

Black protective bitumen coating

The use of bolt clamps to connect electrodes is allowed, but we do not recommend it due to the short-lived result of the electrical connection. After a short time, ground moisture oxidizes the metal at the junction, resulting in the formation of a large transition resistance, which disables the grounding device itself (it does not work). The use of bolted connections in grounding systems is a necessary measure!

Bitumen grease

To connect the Main Ground Bus (GZSh) in the electrical installation room, a transition is made from the steel strip to the grounding conductor (PV-3, PuGV) with a cross-section no less than the phase one and striped markings of yellow-green insulation color. For convenience, the connection point itself on the street is made in a plastic separation box with IP65, preferably at a height of 2.5 meters (out of reach of human touch); The strip steel itself is painted black.

Protective layer of bitumen lubricant from start to finish

Final earthworks

After installation, the trench/pit itself is covered with soft clay-containing soil (without coarse soil/with boulders).

Final earthworks

The use of sandy soil to backfill a horizontal ground electrode worsens the characteristics of the latter, since it creates an area of ​​current spreading around it with a high resistivity. On the contrary, in some cases, to reduce the electrical resistance of the grounding device, it is recommended to fill the space around the horizontal electrode with a low-resistance material/filler (bentonite clay (retains moisture), coke breeze (has low resistivity) and the like).

Measuring work

After completing the final excavation work, measuring work must be carried out: the resistance of the grounding device is measured.

Measuring work

During the installation of deep-modular grounding, after passing every three meters of soil with a grounding electrode, a control check of the grounding resistance is made by direct measurement using a 3-wire method.

When everything is done correctly, the grounding device lasts a long time and its characteristics do not change much depending on the season.

For more detailed information on installing a grounding device, please call: +7 (812) 748-26-28.

Types of grounding, basic conditions

Grounding devices, which form an essential part of the grounding installation, can be natural or artificial, or they are a mixed system consisting of both types.

Natural lands. Natural grounding electrodes can be metal water pipes, lead sheathing and armor of power cables, metal elements built into the foundation, concrete reinforcement in the ground and other metal elements of objects that have good contact with the ground. It is especially recommended to use natural structural reinforcement as grounding in foundations made of concrete reinforced with steel strips or rods embedded in the bottom of the foundation.

Sections, rods, wires, cables, plates or strips can be used as artificial grounding electrodes. Typically, steel coated with conductive protective coatings (anti-corrosion) embedded in the ground horizontally (horizontal ground electrodes) or vertically (vertical ground electrodes), and rods or strips embedded in foundation benches, do not act as structural reinforcement (although their connections made with reinforcement). Ground electrodes can be made of individual horizontal or vertical elements (concentrated ground electrodes) or they can be complex ground electrodes formed from a system of ground electrodes of various configurations (for example, radial, lattice or ring ground electrodes). A system consisting of ground, protective and grounding conductors is called a grounding system. During the installation of grounding loops, the system must be connected to the potential equalization bus of the protected building.

Ground resistance measurement

Content

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1 DEFINITION

2 RESISTANCE OF GROUNDING ELECTRODE

3 INFLUENCE OF ELECTRODE DIMENSIONS AND DEPTH OF ITS GROUNDING

4 INFLUENCE OF SOIL RESISTANCE ON ELECTRODE GROUNDING RESISTANCE

5 FACTORS AFFECTING SOIL RESISTANCE

6 GROUNDING RESISTANCE VALUES

7 PRINCIPLE OF MEASUREMENT OF GROUNDING RESISTANCE

8 POSITION OF AUXILIARY ELECTRODE DURING MEASUREMENT

9 MEASUREMENT OF GROUNDED ELECTRODE RESISTANCE (62 percent method)

10 REMOTEITY OF AUXILIARY ELECTRODE

11 MEASUREMENT OF GROUNDING CONDUCTOR CONDUCTIVITY

12 TWO-POINT MEASUREMENT METHOD (Simplified method)

13 MEASUREMENT OF SOIL RESISTIVITY (4-point method)

14 MEASUREMENT OF SOIL RESISTIVITY WITH THE TERCA 2 DEVICE

15 TOUCH VOLTAGE MEASUREMENT

16 MEASUREMENT WITH S.A 6415 DEVICE USING CURRENT CLAMPS

17 EXAMPLES OF ON-SITE MEASUREMENTS

DEFINITION

The term grounding refers to the electrical connection of any circuit or equipment to the ground. Grounding is used to set and maintain the potential of a connected circuit or equipment as close to ground potential as possible. The ground circuit is formed by the conductor, the clamp by which the conductor is connected to the electrode, the electrode, and the ground around the electrode.

Grounding is widely used for electrical protection purposes. For example, in lighting equipment, grounding is used to short-circuit fault current to ground to protect personnel and equipment components from exposure to high voltage. The low resistance of the grounding circuit ensures that the breakdown current flows to the ground and prompt operation of the protective relays. As a result, extraneous voltage is removed as quickly as possible to avoid exposing personnel and equipment to it. To best maintain the equipment's reference potential to protect against static electricity and to limit voltages on the equipment's frame to protect personnel, the ideal ground circuit resistance should be zero. It will become clear from the following description that this cannot be achieved in practice. Sufficiently low, but not extreme, resistance values ​​are specified in the latest safety standards NEC®, OSHA, etc.

GROUNDING ELECTRODE RESISTANCE

Figure 1 shows a grounding pin. Its resistance is determined by the following components: (A) the resistance of the metal of the pin and the resistance of the contact of the conductor with the pin; (B) contact resistance of the pin with the ground; (B) the resistance of the earth's surface to flowing current, in other words, the resistance of the earth, which is often the most important of the listed terms.

Details: (A) Typically, the grounding pin is made of a highly conductive metal (all copper pin or copper plated) and a terminal of appropriate quality, so the resistance of the pin and its contact with the conductor can be neglected. (B) The National Bureau of Standardization has shown that the electrode-ground contact resistance can be neglected if the electrode is firmly driven in and there is no paint, oil or similar substances on its surface. (B) The last component remaining is the resistance of the soil surface. One can imagine that the electrode is surrounded by concentric layers of soil of equal thickness. The layer closest to the electrode has the smallest surface area but the greatest resistance. As you move away from the electrode, the surface of the layer increases and its resistance decreases. Ultimately, the contribution of the resistance of remote layers to the resistance of the soil surface becomes insignificant. The region beyond which the resistance of the earth's layers can be neglected is called the region of effective resistance. Its size depends on the depth of immersion of the electrode into the ground. Theoretically, earth resistance can be determined by the general formula: R = L / A (Resistance = Resistivity x Length / Area) This formula explains why the resistance of concentric layers decreases as they move away from the electrode: R = Soil resistivity x Layer thickness / Area At When calculating earth resistance, the soil resistivity is considered unchanged, although this is rarely found in practice. Earth resistance formulas for electrode systems are very complex and often provide only approximate resistance calculations. The most commonly used formula for grounding resistance for the case of a single electrode, obtained by Professor Dwight (HR Dwight) from the Massachusetts Institute of Technology: R = /2 L x ((In4L)-1)/r R = , where R is the grounding resistance of the pin in ohms, L – electrode grounding depth, r – electrode radius, – average soil resistivity in Ohm cm.

INFLUENCE OF ELECTRODE DIMENSIONS AND DEPTH OF ITS GROUNDING

Effect of size: Increasing the diameter of the pin reduces the ground resistance slightly. Doubling the diameter reduces resistance by less than 10% (see Fig. 2). Effect of grounding pin depth: Grounding resistance decreases with increasing depth. Theoretically, when the depth is doubled, the resistance decreases by 40%. The NEC standard (1987, 250-83-3) requires that the pin be grounded a minimum of 8 feet (2.4 m) to ensure good ground contact (see Figure 3). In most cases, a 10 ft (3 m) grounded pin will satisfy NEC requirements. The minimum diameter of a steel pin is 5/8 inch (1.59 cm) and that of a copper or copper-plated steel pin is 1/2 inch (1.27 cm) (NEC 1987, 250-83-2). In practice, the minimum diameter of a 3 m ground rod is:

• 1/2 inch (1.27 cm) for regular soil,
• 5/8 inch (1.59 cm) for wet soil,
• 3/4 inch (1.91 cm) for hard ground or for a pin longer than 10 feet.

INFLUENCE OF SOIL RESISTANCE ON ELECTRODE GROUNDING RESISTANCE

Dwight's formula above shows that grounding resistance depends not only on the depth and surface area of ​​the electrode, but also on the resistivity of the soil. It is the main factor that determines the grounding resistance and the depth of grounding of the pin that will be required to ensure low resistance. The resistivity of soil varies greatly depending on the region of the globe and the time of year. It largely depends on the content of electrically conductive minerals and electrolytes in the soil in the form of water with salts dissolved in it. Dry soil that does not contain soluble salts has high resistance (see table No. 1).

Table No. 1

FACTORS AFFECTING SOIL RESISTANCE

Two types of soil in dry form can actually become insulators with a resistivity of more than 109 Ohm cm. As can be seen in table No. 2 , the resistance of a soil sample changes very quickly when the moisture content in it increases to approximately 20%.

Table No. 2
Soil resistivity also depends on temperature. Table No. 3 shows how the resistivity of sandy loam with a moisture content of 12.5% ​​changes when the temperature changes from +20 to -15°C. As you can see, the resistivity varies from 7200 to 330,000 ohm centimeters.

Table No. 3
Since soil resistivity is highly dependent on temperature and moisture content, it is reasonable to assume that the resistance of the grounding device will depend on the time of year. Such changes are shown in Fig. 7 . Since the stability of soil temperature and moisture content improves with distance from the surface, the grounding system will be effective at any time if the pin is driven to a significant depth. Excellent results are obtained when the pin reaches the water level.

Rice. 7 Seasonal variations in ground resistance of a 3/4-inch diameter water pipe in rocky soil. Curve 1 – pipe depth 3 feet, curve 2 – 10 feet.

In some cases, the soil resistivity is so high that obtaining a low grounding resistance requires a complex design and considerable expense. In these cases, it is more economical to use a small ground pin and reduce the ground resistance by periodically increasing the soluble content of the soil around the electrode. Figure 8 shows a significant decrease in the resistance of sandy loam with increasing salt content.

Rice. 8

In Fig. Figure 9 shows the dependence of the resistivity of soil impregnated with a salt solution on temperature. Of course, if brine soaking is used, the ground pin must be protected from chemical corrosion.

Rice. 9

To help the engineer approximately determine the depth of electrode penetration required to obtain a given grounding device resistance, the so-called Grounding Nomogram can be used. It shows that to obtain a ground resistance of 20 ohms on soil with a resistivity of 10,000 ohm-centimeter, a 5/8-diameter rod would need to be buried 20 feet deep.

Working with the Grounding Nomogram

1. Select the required resistance on the R scale.
2. Mark the soil resistivity point on the P scale.
3. Draw a straight line through the points on the R and P scales to the K scale.
4. Mark a point on the K scale.
5. Select the diameter of the pin and draw a straight line to the D scale through the points on the DIA scale and on the K scale.
6. The intersection of this straight line with the scale line D will indicate the amount of pin penetration required to ensure the ground resistance initially selected.

GROUNDING RESISTANCE VALUES

In the section “Resistance of Artificial Electrodes” of NEC ® 250-84 (1987) it is written: “If a single pin, tube or plate electrode does not provide a resistance equal to or less than 25 ohms, then additionally any of the devices described in parts 250-83. Wherever a group of pins, pipes or plates is installed, the specified section requires that the distance between them be at least 1.8 m.” The National Electrical Code (NEC®) specifies that grounding resistance should not exceed 25 ohms. This directive is an upper limit and in many cases a much lower value is required. The question arises: “How low should the ground resistance value be?” It is difficult to name a specific number of ohms. Low ground resistance provides greater protection for personnel and equipment. Therefore, you should strive to make it less than one ohm. However, it would be impractical to achieve such low resistance values ​​throughout the entire power distribution and transmission network or at small substations. In some regions, 5 ohms can be achieved without much effort. In others, it is difficult to achieve even 100 Ohms of grounding resistance. Industry standards stipulate that a power transmission substation must provide a grounding resistance of no more than one ohm. For substations that distribute electricity, a grounding resistance of no higher than 5 or even 1 ohm is recommended. In most substations, the required resistance value can be provided by a grounding system in the form of a grid.

In electric lighting networks or at communication centers, 5 ohms is often considered an acceptable value. If a lightning rod is used in electric lighting networks, it must be connected to a grounding circuit with a resistance of no more than one ohm. It is precisely these values ​​of grounding resistance, resulting from theory, that are usually used in practice. However, there are always cases where it is very difficult to provide grounding resistance that meets NEC ® or other safety standards. For these cases, there are several methods for reducing ground resistance. These include a system of parallel-connected electrodes, a system with deep grounding of composite electrodes, and chemical soil treatment. In addition, other publications discuss grounding in the form of buried plates, conductors (electrical counterweight), in the form of connections to the steel structures of buildings and the reinforcement of reinforced concrete structures.

Low grounding resistance can ensure connection to pipes of water and gas supply systems. However, the recent use of non-metallic pipes and non-conductive joints between pipes has made it difficult or even impossible to ensure low grounding resistance in this case. To measure ground resistance, special instruments are required. Most of them use the principle of potential drop created by alternating current (AC - alternative current) flowing between the auxiliary and the electrode being tested. The measurement is carried out in ohms and shows the resistance between the grounded electrode and the surrounding ground. Among the CA® instruments, ground resistance meters using current clamps have recently appeared.

Note. National electric code ® and NEC ® are registered trademarks of the National Fire Protection Association.

PRINCIPLE OF GROUNDING RESISTANCE MEASUREMENT

(Potential drop principle, 3-point circuit.) A voltmeter measures the voltage between pins X and Y and an ammeter measures the current flowing between pins X and Z (see Fig. 11).

(Note that points X,Y and Z correspond to points X,P and C of a 3-point device or points C1,P2 and C2 of a 4-point device.) Using Ohm's Law formulas E = RI or R = E / I, we can determine the ground resistance of the electrode R. For example, if E = 20 V and I = 1 A, then: R = E / I = 20 / 1 = 20 Ohms If you use a ground tester, you will not need to make these calculations . The device itself will generate the current necessary for the measurement and directly display the value of the grounding resistance.

POSITION OF AUXILIARY ELECTRODE DURING MEASUREMENT

To accurately measure ground resistance, place the current auxiliary electrode Z far enough from the electrode being measured so that the potential at the voltage auxiliary electrode Y is measured outside the effective resistance zones of both the X electrode being tested and the current auxiliary electrode Z. The best way to check whether the electrode is outside the zones of effective resistance of the remaining electrodes, it will take measurements by changing its location. If the auxiliary voltage electrode Y is located in the effective resistance zone of one of the other electrodes (or simultaneously in both zones if the zones overlap), then when its location changes, the instrument readings will change significantly and in this case it is impossible to accurately determine the grounding resistance (see Fig. 12 ).

On the other hand, if the auxiliary voltage electrode Y is located outside the zones of effective resistance (Fig. 13) , then when it moves, the readings will change slightly. This is the best estimate of the ground resistance of electrode X. It is better to plot the measurement results on a graph to ensure that they are on an almost horizontal portion of the curve, as shown in Fig. 13. Often the distance from this area to the electrode being tested is approximately 62% of the distance from the auxiliary current electrode to the electrode being tested.

MEASUREMENT OF GROUNDED ELECTRODE RESISTANCE (62 percent method)

The 62% method was adopted after studying the graphs and practical tests. This method provides the greatest accuracy provided the soil is homogeneous. This method is used when the earthing device under test and two auxiliary electrodes can be placed in line and when the earthing device under test consists of one pin, one pipe, one plate, etc., as shown in Fig. 14.

In Fig. 15 shows that the effective resistance zones (a group of concentric surfaces around the pins) of the tested electrode X and the auxiliary current electrode Z overlap. If you move the Y potential electrode towards the X or Z electrode and repeat the measurement, the readings will vary greatly and the measured value will be unacceptably far from the true ground resistance. The areas of effective resistance intersect and this causes the measured resistance value to increase as electrode X moves away from the electrode being tested Y.

Now consider Figure 16 , in which electrodes X and Z are removed at a distance sufficient so that the effective resistance zones of the electrodes do not intersect. If we now plot the resistance versus the distance between the X and Y electrodes, we can see that the difference between the resistance to the left and right of the 62% point (the relative distance from Y X) is acceptably small. Typically this difference is measured as a percentage of the measured value: ± 2%, ± 5%, ± 10%, etc.

REMOTEITY OF AUXILIARY ELECTRODE

It is impossible to name one value for all cases for the distance from the auxiliary current electrode Z to the electrode being tested X, since it depends on the length and diameter of the electrode being tested, the homogeneity of the soil and, especially, on the size of the effective resistance areas of the electrodes. However, this paragraph gives an approximate value for this distance for a 1-inch diameter electrode with uniform soil (for a 1/2-inch diameter, reduce the distance by 10%, for a 2-inch diameter, increase the distance by 10%).

Approximate distance to auxiliary electrodes for 62% method

MEASUREMENT OF GROUNDING CONDUCTOR CONDUCTIVITY

The conductivity of the ground conductor can be measured by connecting it between two inputs of the measuring device (see Fig. 17).

TWO-POINT MEASUREMENT METHOD (Simplified method)

This alternative method is used when a very good ground other than the one being measured is available. In densely populated areas where it is difficult to find places to install two auxiliary electrodes, the two-point method can be used. The measurement shows the resistance of two grounding devices connected in series. Therefore, the second ground must be very good, so much so that its resistance can be neglected. It is also necessary to measure the resistance of the wire and subtract it from the resulting measurement. The two-point method is not as accurate as the 3-point method (62% method) because it depends on the distance between the electrode being measured and the auxiliary ground (unused ground or water pipe). This method cannot be used as a standard method. Rather, it is a way out of the situation in densely populated areas. See fig. 18.

SOIL RESISTIVITY MEASUREMENT (4-point method)

Why is it so important to measure soil resistance? Measuring soil resistance has a threefold purpose. First, these data are used for geophysical study of underlying rocks to determine zones and depths of ore occurrence and to study other geophysical phenomena. Secondly, soil resistance has a direct impact on the degree of corrosion of underground pipelines. A decrease in soil resistance leads to an intensification of the corrosion process and, therefore, forces special protective treatment of pipes. Thirdly, soil resistance directly affects the design of grounding devices. And that is why the issue of soil resistance is discussed here. When designing large grounding systems, it is wise to identify areas of least soil resistance in order to design the most cost-effective installation. Resistance can be measured using two methods: two-point or 3-point. The two-point method simply involves measuring the resistance between two points. In most cases, the most accurate is the 4-point method, which is used in the Model 4500 Ground Tester. As the name suggests, the 4-point method (see Figures 19 and 20 below) requires four equally spaced electrodes to be placed in a line over the area to be measured. A current of known magnitude flows between the outer electrodes, created by a current generator. The voltage drop between the internal electrodes is measured. Model 4500 directly shows the resistance value in ohms: = 4 AR/ (1+2A/(A2+4B2) -2A/(4A2+4B2)) A – distance between electrodes in cm; B is the depth of grounding of the electrodes in cm. If A > 20 V, then the formula is: = 2 AR (if A is in cm) = 191.5 AR (if A is in feet) = Soil resistance (in Ohm cm) This the value is the average soil resistivity at a depth equal to the distance A between the electrodes.

MEASUREMENT OF SOIL RESISTIVITY WITH THE TERCA 2 DEVICE

There is a vast area of ​​land on which it is necessary to determine the place with the best resistivity. A little intuition won't hurt. Since our goal is to find a place with the least resistance, we prefer moist loam to dry sandy soil. You should also estimate the depth of the layer with the lowest resistivity. Example: After the survey, the search area was reduced to approximately 75 square feet (22.5 m?). Let's say you want to determine the resistivity at a depth of 15 feet (450 cm). The distance between the outermost ground pins is equal to the depth at which the average resistivity is to be measured (15 feet or 450 cm). To apply the simpler Wehner formula (r = 2? AR), it is necessary to ground the electrode to a depth equal to 1/20 of the distance between the electrodes or 8 7/8 feet (22.5 cm). Install the electrodes along the grid, as shown in Fig. 19 , and connect the Model 4500 Ground Tester according to the diagram in Fig. 20. Follow these steps:

• Remove the jumper connecting terminals X and X V (C1 and P1) of the device;
• Connect the device to all four pins (see Fig. 20).

For example, let the measured resistance be R = 15, (resistivity) = 2 RA A (distance between electrodes) = 450 cm. Then: = 6.28 x 15 x 450 = 42,390 Ohm cm.

TOUCH VOLTAGE MEASUREMENT

The first reason to measure touch voltage is to assess the safety of personnel and the protection of equipment from high voltage. However, in some cases, the degree of electrical safety can be assessed from different points of view. Periodic measurements of the resistance of a grounding device in the form of an electrode or an array of electrodes are recommended in the following cases:

1. When the grounding device in the form of an electrode or grid is relatively small and it is convenient to disconnect it.
2. When there is a suspicion that the electrode is corroding, caused by low soil resistance and galvanic processes.
3. When a breakdown to ground in the vicinity of the grounding device being tested is unlikely. Measuring touch voltage is an alternative way to determine safety. It is recommended in the following cases:
4. When it is physically or economically impossible to disconnect the grounding in order to make a measurement.
5. When can ground faults be expected near the ground being tested or near equipment that is connected to the ground being tested.
6. When the “footprint” of the equipment is comparable to the size of the grounding that is to be checked. (“Trace” is the outline of that part of the equipment that is in contact with the ground.)

Neither measuring ground resistance by the potential drop method nor measuring touch voltage indicates the ability of the ground conductor to withstand large leakage currents from the phase conductor to the ground conductor. Another test using high current is required to check this. A 4-point ground tester is used to measure touch voltage. During the measurement process, the device generates a small voltage in the ground, simulating a fault voltage near the point on the ground being tested. The device displays the value in volts per ampere of current flowing in the grounding circuit. The displayed value is then multiplied by the maximum current expected in the ground to calculate the worst case touch voltage of the installation. For example, if, when testing a system with a maximum expected fault current of 5000 A, the device showed a value of 0.100, then the touch voltage will be equal to 500 V. Measuring the touch voltage is similar to the potential drop method in that it also requires the installation of auxiliary electrodes in the ground or on its surface . But the distance between the auxiliary electrodes will be different - see fig. 21.

Consider the following example. Let the insulation of the underground cable shown in the figure be broken not far from the shown substation. Currents will appear in the ground caused by the accident, which will flow to the substation grounding device, creating a potential difference. This voltage can be dangerous to the health, and even life, of personnel located on this piece of land. To roughly measure the touch voltage for a given situation, follow these steps: Connect the cables between the substation fence and points C1 and P1 of the 4-point ground tester. Install the electrode in the ground at a point. where you can expect a breakdown of the cable and connect the electrode to terminal C2 of the device. Install another electrode in the ground in the line between the first electrode and the connection point to the fence at a distance of one meter (or arm's length) from the point of connection to the fence and connect this electrode to point P2 of the device. Turn on the device, select the 10 mA range and take a measurement. Multiply it by the maximum possible current in case of an emergency. By installing an electrode connected to terminal P2 of the device in various places around the fence adjacent to the faulty line, you can obtain a map of potential changes.

MEASUREMENT WITH S.A 6415 DEVICE USING CURRENT CLAMPS

This is a new and unique method for measuring ground resistance. It allows measurements to be taken without disconnecting the ground circuit. In addition, the advantage of the method is that it allows you to measure the total resistance of the grounding device, including the resistance of the connections in the ground circuit.

Fig.22

Fig.23

Typically, the grounding conductor of a general purpose electrical network can be represented by the circuit shown in Fig. 22 or an equivalent circuit shown in Fig. 23 . If voltage E is created in any branch with resistance RX using a transformer, current I will flow through the circuit. The described quantities are related by the relation E / I = RX. With a known constant voltage E, the resistance RX can be obtained by measuring the current I. Let us turn again to Fig. 22 and 23 . The current is created by a special transformer connected through a power amplifier to a voltage source with a constant amplitude and frequency of 1.6 kHz. This current is recorded in the resulting circuit. The measured signal is recorded by a synchronous detector, amplified by a selective amplifier, converted by an analog-to-digital converter and displayed on an LCD display. A selective amplifier is used to purify the useful signal from signals with the mains frequency and from high-frequency noise. The voltage is sensed by coils surrounding the conductor in the circuit being excited, then amplified and cleared when compared to a reference signal in a comparator. If the clamps are not closed correctly, the message “open jaws” appears on the display.

EXAMPLES OF ON-SITE MEASUREMENTS

MEASUREMENT OF GROUNDING OF A TRANSFORMER MOUNTED ON A POWER LINE POLAR Remove the protective cap from the grounding wire and provide enough free space for the clamp to grip the conductor. The pliers must freely grip the grounding conductor. You can also grab the grounding pin directly with pliers. Note: The clamp must be in the electrical path from the system neutral or grounding conductor to the pin or pins (depending on version) Select current measurement "A". Grab the grounding conductor with a clamp and measure the current in the conductor. The maximum value is 30 A. If the current value exceeds 30 A, ground resistance measurement is not possible. Stop measuring. Remove the SA 6415 device from this point and continue measuring at other points. If the current measured in the grounding circuit does not exceed the permissible value, select the “?” device and read the measurement result in ohms. The measured value corresponds not only to the resistance of the grounding system, but also includes the resistance of the neutral-to-pin contact and all connections between the neutral and the pin. Note that in Figure 24, grounding is provided by the end of the post and the ground pin. It is necessary to connect the clamps above the connection point of the conductors from the end of the pole and from the pin in order to measure the total grounding resistance of both ground electrodes. For subsequent reference to the result, write down the date, current, ground resistance in ohms and pole number.

Note: Large resistance value may be caused by:

A) poor grounding of the pin; B) disconnected grounding conductor; B) high resistance of contacts or conductor splices; inspect the pliers, the connection at the end of the pin, for deep cracks at the joints.

MEASUREMENT OF GROUND AT JUNCTION BOX OR ELECTRICITY METER Follow basically the above procedure. Notice in fig. 25 that grounding can be performed in the form of a group of pins or, as shown in Fig. 26 , a water pipe coming out of the ground can be used as grounding. Both types of grounding can be used simultaneously. In this case, the measurement point at the neutral should be selected so as to measure the total ground resistance of the system. GROUNDING MEASUREMENT ON A TRANSFORMER INSTALLED ON SITE

• Comment. Never open the transformer guard. This is the property of the public utility. This measurement can only be performed by a specialist.
• Follow all necessary safety precautions.
• Dangerous voltage is present.

Identify and count all ground pins (usually there is a single pin). If the grounding pins are inside the guard, refer to Fig. 27 , and if outside the fence - to Fig. 28. If there is a single ground pin and it is located inside the fence, then the measurement should be made by connecting to the conductor immediately after the conductor makes contact with the pin. Often, several conductors return from the clamp on the pin to the neutral or inside the fence.

In many cases, the best measurement can be obtained using a 3710 or 3730 clamp connected directly to a ground pin. In this case, only the resistance of the grounding device is measured. Connect clamps only at the point where there is only one path for current to flow to the neutral. Typically, if you get a very low resistance reading, it means you have connected to a loop and you should move your measurement point closer to the pin. In Fig. 28 ground pin outside the fence. To get the correct result, select the clamp connection point as shown in the figure. If there are several pins in different corners inside the fence, you need to determine how they are connected in order to choose the correct measuring point.

TRANSMISSION STANDS Observe all necessary safety precautions. Dangerous voltage is present. Locate the ground conductor near the rack foundation. Note that there are many configurations. Be careful when identifying grounding conductors. In Fig. Figure 29 shows one rack on a concrete foundation with an external ground conductor. The clamp connection point must be located above the electrical connection point of the parts of the grounding system, which can be made in the form of a group of pins, plates, turns or foundation elements.

Source of information: https://www.diagnost.ru/

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Materials for the construction of grounding electrodes

Current regulations allow the possibility of manufacturing grounding electrodes from galvanized steel, electrolytically coated copper or pure copper. Copper is often used as a material for protective coatings on steel grounding electrodes. However, none of the standards mention galvanized steel approved materials. The thickness of coatings is also regulated by standards. They are different for different materials, they also depend on how the elements are laid. Others are for horizontal trenches and others are for vertical trenches.

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Implementation of ring grounding

The ring grounding electrode, that is, the Type B system, is most often made of galvanized steel strip, immersed at least 0.5 meters deep, at a distance of about 1 meter from the external walls of the protected object. The tape must be a closed system. When using a grounding electrode for surge protection purposes, the installation depth should be below the ground's freezing zone, that is, at least 0.7 meters deep. This is due to the fact that the resistivity of frozen soil is significantly higher than normal. Fortunately, research shows that the actual depth of soil freezing is less than predicted by standards.

All connections, including grounding conductors, must be secure and protected from corrosion. If it is not possible to close the perimeter of the rim, parts of the rim can be made. But the open ends of the rim must be covered with vertical ground electrodes.

Grounding. What is it and how to make it (part 2)

1 part. Grounding (general information, terms and definitions)

Part 2. Traditional methods of constructing grounding devices (description, calculation, installation)

Part 3. Modern methods of constructing grounding devices (description, calculation, installation)

Part 2. Traditional methods of constructing grounding devices (description, calculation, installation)

In this part I will talk about traditional/classical methods of constructing ground electrodes, used around the beginning of the twentieth century.

D. Basic construction methods

G1. Several short electrodes (“angle and sledgehammer”)

G1.1. Features of the solution

G1.1.1. Soil freezing in winter G1.1.2. Mutual “shielding”/“shading” of electrodes

G1.2. Calculation of the resulting grounding resistance and the required number of grounding electrodes G1.3. Installation G1.4. Advantages and disadvantages of G1.5. Reducing the number of electrodes

G2. Single depth electrode (“casing”)

D2.1. Feature of solution G2.2. Calculation of the resulting grounding resistance G2.3. Installation G2.4. Advantages and disadvantages

D. Basic construction methods

Let me remind you that in the last part I focused on the general approach...

When constructing grounding electrodes, vertical grounding electrodes are most often used.
This is due to the fact that horizontal electrodes are difficult to bury to a great depth, and at a shallow depth of such electrodes, their grounding resistance greatly increases (deterioration of the main characteristic) in winter due to the freezing of the top layer of soil, leading to a large increase in its specific electrical resistance. Steel pipes, pins/rods, angles, etc. are almost always chosen as vertical electrodes. standard rolled products having a large length (more than 1 meter) with relatively small transverse dimensions. This choice is due to the possibility of easily deepening such elements into the ground, unlike, for example, a flat sheet.

There are two main traditional methods/solutions for constructing ground electrodes. Both are based on the use of vertical grounding electrodes.

G1. Several short electrodes (“angle and sledgehammer”)

With this approach, small (2-3 meters) steel angles/pins are used as grounding electrodes.
To create a grounding system, they are connected together near the soil surface with a steel strip by welding it to these elements using electric or gas welding. The electrodes are driven into the ground by simply hammering them in with a sledgehammer, which is in the hands of a physically strong and resilient installer. Therefore, this solution is widely used under the code name “corner and sledgehammer”.

A large contact area between the ground electrode and the ground (that’s what I’m talking about) is achieved by a large number of electrodes ( multi-electrode ground electrode

). It is very difficult to increase the depth of the electrodes (an alternative way to increase the contact area), because As the depth increases, the friction force between the mounted electrode and the ground increases, and the weight of the sledgehammer and the force of the installer have a limit.

When choosing angles/pins and other suitable metal products, it is necessary to take into account their corrosion resistance and the ability to pass large currents through them for some time without melting.

The minimum permitted transverse dimensions (sections) of grounding electrodes are described in Table 1.7.4 of the PUE, but in recent years, corrected and supplemented values ​​from Table 1 of Technical Circular 11 of 2006 of the RosElectroMontazh Association have been more often used (sources).

In particular:

• for a corner or rectangular profile (strip) made of black steel, the cross-section must be at least 150 mm2 with a minimum wall thickness of 5 mm
• for a round rod made of black steel, the minimum diameter should be 18 mm
• for a pipe profile made of black steel, the minimum diameter must be 32 mm with a minimum wall thickness of at least 3.5 mm

G1.1. Features of the solution

When increasing the number of electrodes, it is necessary to take into account some features.

G1.1.1. Soil freezing in winter

In winter, due to the freezing of the soil to the depths at which half the length of the electrodes is located (and this is up to 2 meters), the resistance of such a ground electrode increases. To compensate for this increase (to maintain satisfactory grounding quality), the ground electrode is made with a sufficient “reserve” of electrodes. For example, for three-meter electrodes, a twofold
increase in quantity is required.

G1.1.2. Mutual “shielding”/“shading” of electrodes

In addition, by increasing the number of electrodes it is necessary to compensate for the increase in the number of electrodes. This negative point is the so-called.
“shielding”/“shading” occurs when using multiple grounding electrodes and does not allow closely located electrodes to fully “dissipate” the current into the surrounding soil. Expressed as a coefficient of utilization of the conductivity of the ground electrode (link to a third-party site). For example: ten

electrodes 3 meters deep, located in a line at a distance of 3 meters (i.e. at a distance = their depth) from each other “work” at 60% of their maximum efficiency. Ten of the same electrodes, located at a distance of 6 meters (i.e. at a distance = their double depth) from each other “work” at 75% of their maximum efficiency. One hundred percent efficiency is achieved by distancing the electrodes at a distance of about 30 meters (10 of their depths), which in practice is never used for the sake of the desire for adequate compactness and the cost of installing a grounding device.

G1.2. Calculation of the resulting grounding resistance and the required number of grounding electrodes

I will describe the calculations using the example of the ten
most commonly used
three-meter
electrodes for this method in the form of a steel equal-flange angle with a shelf width of
50 mm
, mounted at a distance of
3 meters
from each other in a ditch 0.5 meters deep (in paragraph D1.3. explanation "why is that").
The soil in which these electrodes will be mounted will be loam, common in Russia, with an electrical resistivity of 100 Ohm*m
.

The calculations are not complicated and are carried out in 3 stages.

The resulting grounding resistance
is stage 1.
First you need to calculate the grounding resistance of one grounding electrode. The grounding resistance of a single vertical grounding electrode is calculated by the formula:

R1 will be 27.8 Ohm (at p = 100 Ohm*m, L = 3 m, d = 0.05 m (50 mm; for flat electrodes, diameter means their width), T = 2 m (T is the distance from the upper ground level to the middle of the buried electrode)).

Stage 2.

The total resistance of several electrodes under ideal conditions will be less than the grounding resistance of one electrode by as many times as there are electrodes.

For ten electrodes, the total resistance will be 10 times less and will be 2.78 Ohms.

Stage 3.

“Compensation”.
The seasonal coefficient (increase in grounding resistance in soil frozen in winter) for such electrodes will be equal to 2
(where does this come from).
The coefficient of utilization of the conductivity of the electrodes will be equal to 0.6
, because the distance between the electrodes will be 3 meters (i.e. equal to the depth of the electrode), and their number will be 10 pieces (where does this come from). Both coefficients increase the ground resistance.

The final total grounding resistance of the above 10 electrodes will be equal to 5.56 Ohms

in summer and
9.27 Ohms
in winter.

Required number of grounding electrodes

Let's imagine that our task is to ground telecommunications equipment and for this we need to obtain grounding with a resistance of no more than 4 ohms.

Stage 1.

All repeats. We calculate the grounding resistance of one/single grounding electrode.

R1 will be 27.8 ohms.

Stage 2.

The number of electrodes under ideal conditions directly depends on the required grounding resistance, rounded up (“ceiling”).

To achieve 4 ohms, the number of electrodes will be 7 pieces (rounding 6.95).

Stage 3.

“Compensation”.
The seasonal coefficient (increase in grounding resistance in soil frozen in winter) for such electrodes will be equal to 2
.
The coefficient of utilization of the conductivity of the electrodes will depend on the calculated number of electrodes - it cannot be selected in advance. However, you can estimate the worst case scenario and, assuming that there will be more than 20 electrodes, take the value of 0.5
. Both factors increase the required number of grounding electrodes.

The total required number of the above grounding electrodes will be 28 pieces

(rounded to 27.8).
The coincidence with the grounding resistance of one electrode is accidental.

G1.3. Installation

The installation of the multi-electrode ground electrode described above looks something like this.

1. From the point where the grounding conductor is inserted into the building/object, a ditch 84 meters long (28 electrodes per 3 meters) with a depth of 0.5-0.7 meters is dug along the perimeter/contour of this building along its walls at a distance of 1 meter.
2. Into this ditch, at a distance of at least 3 meters from each other, 28 pieces of steel angles or pieces of reinforcement 3 meters long, pre-sharpened on the bottom side (with a grinder), are hammered with a sledgehammer.
3. After all the electrodes are driven in, a grounding conductor is laid in the ditch from the entrance to the building (where the electrical panel is located) to the farthest electrode. Typically, with this method, the conductor is a 4*50 mm steel strip.
4. The strip is welded to the electrodes with a high-quality (!) long seam.
5. The welding area is covered with a layer of bitumen or anti-corrosion paint, because it has a tendency to quickly corrode in the ground.
6. The ditch is filled up.
7. Outside or inside the building, a transition is made from a steel strip to a copper wire connected to the electrical panel. For low powers it is usually done like this:

A 0.5-0.7 meter recess (ditch) is necessary for mechanical and weather insulation of the conductor (strip) and the tops of the electrodes.
For example, so as not to damage them when digging soil for a flower garden and so that the steel gets less wet during rain (this allows you to reduce its corrosion, and therefore increase its service life). The mutual distance between the electrodes of at least 3 meters is some measure to counteract the effect of “shielding”/“shading” of the electrodes from each other.

The use of welding to connect elements made of black steel is strongly recommended by the PUE (clause 1.7.139).

Materials used:

• steel corner with a width of 50 mm and a wall thickness of 5 mm = 84 meters
• or pieces of smooth steel reinforcement with a diameter of 18 mm = 84 meters
• steel strip 4*50 mm = about 85 meters
• bitumen or anti-corrosion paint

Tool used:

• shovel
• heavier sledgehammer (4-5 kg)
• welding machine

Resources used:

• strong and resilient installer
• installer with welding skills

G1.4. Advantages and disadvantages

Advantages:

• simplicity
• low cost of materials and installation
• availability of materials and installation

Flaws:

• high cost of delivering the material to the site (cannot be placed in a passenger car due to the size and weight of the materials)
• the need to use a large amount of brute force (digging a ditch, swinging a sledgehammer)
• Welding is required, which means a welding machine and a person with welding skills. The situation is aggravated when there is no electricity at the site.
• large area occupied by the ground electrode: often several tens of meters near the building (ten 3-meter electrodes will have to be located in a ditch 27 meters long)
• short service life of electrodes of 5-15 years (especially in soils with high groundwater). An increase in transverse dimensions (steel thickness) is fraught with an increase in installation complexity.
• inconvenient installation, because when using even 2-meter electrodes, at the beginning of driving, you need to stand on some kind of bench/ladder and from there “swing a sledgehammer”
• impossibility of installation in rocky soil

G1.5. Reducing the number of electrodes

Sometimes, together with this solution, a method is used to radically reduce the electrical resistivity of the soil, which makes it possible to reduce the number of grounding electrodes by 2-3 times while maintaining the resulting grounding resistance.
In other words, this method can significantly reduce grounding resistance. We are talking about salinizing the soil at the location of the electrodes by adding a large volume of table salt NaCl to it (on average - 5 kilograms per meter of the length of the ditch in which installation is being carried out). When it dissolves in the soil (leaching (wiki)), the concentration of ions involved in charge transfer sharply increases, and therefore its (soil) electrical resistance decreases. Despite the undeniable positive advantages of this method, as well as its simplicity and low cost, it has two huge disadvantages

, which threaten to restore the grounding system practically “from scratch”:

• Due to the leaching of salt from the soil (rains, spring melting of snow), the concentration of ions drops to the natural level in 1-3 years
• salt causes severe corrosion of steel, destroying the electrodes and grounding conductor in 2-3 years

G2. Single depth electrode (“casing”)

D2.1. Features of the solution G2.2. Calculation of the resulting grounding resistance G2.3. Installation G2.4. Advantages and disadvantages

With this approach, the ground electrode is a deep electrode (most often single) in the form of a steel pipe placed in a hole drilled in the ground.
Drilling and placement into the pipe hole is carried out by a special machine - a drilling rig (usually based on a truck). A large area of ​​contact between the ground electrode and the ground (that’s what I’m talking about) is achieved by the large length (or rather, depth) of the electrode. In addition, due to reaching deep layers of soil, which in most cases have lower electrical resistivity, this method has greater efficiency (lower grounding resistance) than the first - with the same total length of the electrodes.

D2.1. Features of the solution

When increasing the depth of the electrode, it is necessary to take into account that in homogeneous soil the grounding resistance decreases not in proportion to this increase (greater depth -> less decrease in resistance).

Therefore, in the absence of soil layers with lower electrical resistivity at depth, it is worth considering increasing the number of electrodes rather than increasing the depth of a single electrode. The solution to this issue will be influenced by the cost of installing additional electrodes and the availability of space for their placement.

But let me remind you (original): ... in practice, in more than 70% of cases, soil at a depth of more than 5 meters has several times lower electrical resistivity than at the surface, due to higher humidity and density.

D2.2. Calculation of the resulting grounding resistance

I will describe the calculations using the example of a single thirty-meter
electrode in the form of a steel pipe with a diameter of
100 mm
, mounted in a ditch
0.5 meters
.
To simplify the calculation, the soil in which this electrode will be mounted will be homogeneous loam, common in Russia, with a specific electrical resistance of 100 Ohm*m
.

The calculation is carried out in 1 stage.

The grounding resistance of a single vertical grounding electrode is calculated by the formula:

R1 will be 3.7 ohms

(at p = 100 Ohm*m, L = 30 m, d = 0.1 m (100 mm), T = 15.5 m (T is the distance from the top ground level to the middle of the buried electrode)).

Compare with the result in section D1.2. Even under the condition of homogeneous soil, a single deep ground electrode turns out to be much more effective than a multi-electrode one, which will affect the huge difference in the area occupied by this ground electrode on the surface. But in this “euphoria” we should not forget about the cost of drilling operations, which I will mention below in paragraph D2.4. ("Flaws").

D2.3. Installation

In practice, the installation of such a ground electrode is somewhat simpler than the installation of a multi-electrode ground electrode from the first solution ().

1. From the point where the grounding conductor is inserted into the building/object, at a distance of 3 meters (for safe access to the installation), a ditch 3-4 meters long and 0.5-0.7 meters deep is dug to the side perpendicular to the wall.
2. The drilling rig drills and installs the electrode (“casing”).
3. A grounding conductor is laid in the ditch from the entrance to the building (where the electrical panel is located) to the electrode. Typically, with this method, the conductor is a 4*50 mm steel strip.
4. The strip is welded to the electrode-pipe with a high-quality (!) long seam.
5. The welding area is covered with a layer of bitumen or anti-corrosion paint, because it has a tendency to quickly corrode in the ground.
6. The ditch is filled up.
7. Outside or inside the building, a transition is made from a steel strip to a copper wire connected to the electrical panel. For example, as described in paragraph D1.3.

Materials used:

• steel pipe with a diameter of 100-200 mm with a wall thickness of 3.5-5 mm = 30 meters
• steel strip 4*50 mm = about 5 meters
• bitumen or anti-corrosion paint

Tool used:

• drilling rig
• shovel
• welding machine

Resources used:

• installer with welding skills

D2.4. Advantages and disadvantages

Advantages:

• high efficiency
• compactness, because no need to “fence” many electrodes
• seasonal INDEPENDENCE of grounding quality. In winter, due to soil freezing, the resistance of such a ground electrode almost does not change due to the location of no more than 5-10% of the electrode length in the zone of freezing soil.

Flaws:

• high cost of drilling work (from 1500-2000 rubles per meter of drilling). The electrode given in the calculations (section D2.2.) will cost 50-60 thousand rubles.
• (as with the first method) welding is required, which means a welding machine and a person with welding skills.
• (as with the first method), the electrodes have a short service life of 5-15 years (especially in soils with high groundwater). When using a thick-walled pipe, it is possible to increase it to a longer period, but this causes an increase in the cost of this pipe.

Modern technologies

Tradition is progress in the past;
in the future, progress will become a tradition (Edouard Herriot) At the end of the twentieth century, a solution was developed that has the advantages of both methods described above, without having their inherent disadvantages.

In addition, the strong influence of soil salinization on reducing grounding resistance (section D1.5.) attracted the attention of engineers so much that a “cure” was found for the shortcomings of this method - leaching of salt from the soil and corrosion of electrodes. It gave rise to a very interesting method of constructing a ground electrode, applicable where simple metal electrodes pass - in permafrost and rocky soils.

I will talk about them in the next, final, part.

UPD: Additional information on grounding in private homes

For those who live in private houses. /Invigorate/ Guys, don’t panic because of the large number of grounding electrodes in the example. There I calculated a device with a resistance of no more than 4 ohms. These are very strict requirements. To ground the electrical network of a private house, it is enough to build a grounding with a resistance of no more than 10 ohms. That's why:

1. This resistance is optimal from the point of view of the operation of circuit breakers
2. This resistance is enough to connect lightning rods to the device (well, you never know, maybe you want to)
3. This resistance is sufficient to ensure guaranteed operation of SPDs, which are recommended to be installed in the switchboard at the entrance to the house. SPDs are needed to protect your electrical equipment from surge voltages when lightning strikes an overhead power line somewhere along the line from the transformer

10 Ohm is much easier to get. This is only 10 electrodes. Half a day of normal work.

Alexey Rozhankov, technical specialist

The following materials were used in preparing this part:

• Publications on the website “Grounding on ZANDZ.ru”
• Rules for the Construction of Electrical Installations (PUE), part 1.7 as amended by the seventh edition (Google)
• Technical circular 11/2006 of the association "Roselectromontazh" (google)
• Own experience and knowledge

Vertical ground electrodes

Vertical grounding electrodes are made of pipes or specially prepared rods sunk into the ground so that their upper ends are below ground level. It is recommended that the distance between the individual elements of the grounding electrode be at a distance not less than their length. Vertically driven ground electrodes are especially useful when soil resistivity decreases with increasing depth. Their driving depth is usually about 2.5 meters, however there are ground electrodes that are 7 meters long. Further increasing this measurement rarely brings noticeable benefits. If the resistance of the ground electrode is made higher than required, the next one must be immersed and connected to the first in parallel.

The distance between these elements should be:

• equal to at least their length in the case of two vertical elements;
• greater spacing with more vertical elements.

If there is a risk of freezing or drying out of the soil, the length of the vertical elements should be increased by 1 or 2 meters.

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The elements connecting the individual parts of the vertical ground electrode must have the same mechanical strength as the rods or pipes of the ground electrode, and must also be resistant to mechanical stress during impact.

Hammering of grounding electrodes

Grounding electrodes are driven into the ground using special-purpose machines (see below), or commercially available electric and pneumatic hammers, electric rammers, petrol hammer drills, light pile drivers, vibrators and other impact and vibration-impact mechanisms are used for this purpose, as well as manual devices for installing single grounding electrodes. in remote places.

When driving, you can use steel electrodes of any profile - angle, square, round, however, the lowest metal consumption (with the same conductivity) and the greatest resistance to soil corrosion (in the case of equal metal consumption) are achieved when using rod electrodes made of round steel.

When driving into ordinary soils to a depth of up to 6 m, it is rational and economical to use rod electrodes with a diameter of 12-14 mm. With the required depth of up to 10 m, as well as when driving short electrodes into particularly dense soils, more durable electrodes with a diameter of 16 to 20 mm are required. Using impact mechanisms, it is difficult to drive electrodes deeper than 10 - 12 m. To do this, it is more rational to use shock-vibration mechanisms - vibrators, with the help of which the electrodes can be easily immersed even in frozen soil, which loses its strength under the influence of vibration.

Vibrators can immerse the electrodes much deeper than when screwing and pressing. This is especially important for soils with high resistivity (about 1000 Ohms) and deep groundwater levels (more than 9 m), for example for dry sand, in which the electrode resistance decreases very sharply as it goes deeper:

• Electrode driving depth, m. . . 3.5 5 7 9 11 13 15 18
• Resistance to spreading. Om. . . 300 250 20 10

From these figures it can be seen that one vertical electrode immersed to a depth of 18 m will have approximately the same conductivity as 30 electrodes immersed to a depth of 3.5 m. Considering the jumpers required to connect short electrodes, much more metal will be needed both labor costs and the cost of the grounding device will increase significantly, and the conductivity due to the mutual shielding of short electrodes may be even worse than that of a single deep electrode.

If the soil was not probed during design and the electrical characteristics of the soil are unknown, then in order to avoid unnecessary work, it is recommended to install deep grounding electrodes in the following sequence:

• prepare the electrode sections. Their length should be taken according to the design of the mechanism used;
• hammer in the lower section of the electrode;
• measure the spreading resistance of the clogged section;
• weld the next section of the electrode;
• score the second segment and measure again;
• Continue work until the desired conductivity is achieved.

Using a mechanical vibrator mounted on a tractor (Fig. 1a), round steel electrodes with a diameter of 18–20 mm were immersed to a depth of 18 m. A welding generator was also installed on the same tractor.

Rice. 1. Driving vertical grounding electrodes: a, b - mounted mechanical or electric vibrator; c, d - an electric vibrator mounted on an electrode or on springs; d, f - with an electric hammer mounted on a composite or solid electrode; 1 — vibrator; 2 — lifting boom; 3 - flexible drive shaft; 4 — clutch; 5 tractor power take-off shaft and belt drive to the welding generator and to the vibrator drive clutch; 6—submersible ground electrode; 7 — striker pipe; 8—platform with upper striker; 9 — spring; 10 — electric hammer; 11 — plug-in firing pin; 12— coupling; 13— trestles with fencing; 14 — guide angle; 15 — clamp

A mechanical vibrator weighing 8 kg has a round body with a diameter of 100 mm, in which the unbalance rotates on two bearings. By means of an intermediate striker attached to the body on spiral springs and a tubular tip, the impacts are transmitted to the immersed electrode.

The vibrator is suspended from the tractor on a light folding jib. It is driven into rotation by the tractor engine through an additionally installed clutch and a flexible shaft with a diameter of 16 mm. This vibrator design is not balanced in the horizontal plane, and therefore the length of the immersed segment is determined by the height of the vibrator suspension to the jib. With a balanced design, the electrode passed through this structure could be solid, but off-road transportation and installation for immersion of long straight rods is difficult, and on-site welding is necessary in all cases. The absence of power trains or moving parts in the vibrator, other than a single massive imbalance, makes it extremely reliable. There are no exposed moving parts in the work area, and there is no compressed air or electrical voltage. This increases worker safety.

In one step, a section of the electrode 2-2.5 m long was immersed, then the vibrator was raised, the next section was increased by welding, and immersion continued until sufficient conductivity of the ground electrode was achieved. The work cycle - immersing the electrode by 2.5 m and increasing it - depending on the density of the soil and the depth reached, took from 2 to 7 minutes.

In other cases, an electric vibrator is used, suspended from a crane boom mounted on a vehicle (Fig. 1, b). To perform welding work, a welding transformer is installed in the body of the machine, and an electric generator is installed to power the transformer, boom drive and vibrator. The installation control buttons are mounted on the car wall in a protective casing. The boom with a lifting capacity of 0.5 tons is placed on the roof of the van. Raising the vibrator takes 2 minutes, and immersing a 3 m long piece of electrode made from waste pipes takes about 5 minutes.

For a factory-produced electric vibrator, a guide cup is additionally manufactured with a cylindrical adapter for round-section electrodes or with an adapter mounted on an electrode made of angle steel or steel of a correspondingly different profile.

Electric vibrator power - 1.2 kW, weight - 100 kg. The power of the electric motors on the lifting winch and boom is 1.7 and 1.0 kW, respectively.

The vehicle is equipped with a 25 kW electric generator that provides power to the vibrator, electric motors and welding transformer. The ground loop is installed using such an installation by a team of two workers, one of whom is a driver, and the other has a combined profession of a mechanic and welder. Both are trained in how to inspect, measure and test the quality of the ground electrode. The unit mounts the electrodes, welds them into a circuit, checks it and draws up a measurement protocol and an inspection report of the ground electrode (fills out forms).

The same method of immersing a small number of electrodes can be used without a specially equipped car or tractor, using a lightweight vibrator with a power of up to 0.8 kW, installed in the working position together with the immersed electrode with the effort of one or two workers. The use of a special metal stand (Fig. 4, c) allows workers not to touch the device while immersing the electrode, which greatly facilitates the work.

Another device for driving electrodes, also having a small vibrator, is shown in Fig. 1, g. Two car springs are fastened with brackets. On the upper spring there is a platform on which a vibrator with a striker-holder for the electrode is placed. On the lower spring there is a similar platform with a piece of pipe that serves as another striker. During operation of the vibrator, the strikers collide, for which there must be a sufficient gap between them. Grounding electrodes can be used of any profile, but the easiest way is to use rod electrodes, which make it easier to manufacture strikers.

The grounding electrode is freely inserted through the striker pipe into the upper striker holder until it stops. Then the vibrator is turned on, and with each blow the electrode is immersed in the ground to a depth equal to the gap between the strikers, and the entire device falls down under the influence of its gravity. The gap between the strikers is restored by the recoil force and elasticity of the springs. When the device, which descends along with the electrode, approaches the surface of the earth, the vibrator is turned off and the device is removed. If the depth of immersion of the ground electrodes is insufficient, then the next piece of round steel is welded to the clogged earth electrode and the driving process is repeated.

A rod electrode with a diameter of 16 mm and a length of 4 m is driven into medium-density soil in 5 minutes, and a rod electrode with a length of 8 m in 20 minutes, including the time for welding the electrode sections. The device can be used to hammer not only round steel, but also pipes and steel of other profiles, if for this purpose a striker-holder and an electrode guide pipe of the appropriate dimensions are placed in the device.

We have accumulated extensive experience in driving grounding conductors using electric hammers and pneumatic hammers, mass-produced by factories. Using a mobile electric generator or compressor, you can put 2-3 or more hammers into work at the same time, speeding up the work.

In the workshop, sections of rod electrodes 2.5 m long are prepared in advance and a coupling made of a pipe of the appropriate diameter and length of 100 mm, cut from either side to the wall thickness lengthwise, is welded to one end of each section. The slot is needed for the longitudinal weld.

When preparing electrodes, they are inserted into the coupling by 50 mm, the end of the coupling is welded to the electrode along its circumference with a transverse seam and with a longitudinal seam 50 mm long along the slot in the coupling. The second half of the coupling length remains free for ease of connecting sections and driving. An electric hammer (Fig. 1, e) with a striker inserted into it, its end entering the upper half of the coupling, is securely held in it and, vibrating under the influence of its own mass when the energy source is turned on, hammers the electrode.

During the driving process, you do not need to hold the electric hammer with your hands, which makes the work much easier. But to install an electric hammer weighing up to 21 kg on an electrode placed vertically on the ground, durable, stable portable trestles with a fencing of the working area are required.

After the electrode is immersed to its upper end, the hammer is turned off, removed from the electrode and the lower end of the next section of the electrode is inserted into the upper half of the coupling, welded with transverse and longitudinal seams to the clogged electrode and the immersion continues by installing the electric hammer in the coupling available at the upper end of the second segment.

The work of making couplings and the cost of pipes or sheet steel sometimes seem unnecessary to installers, and they prefer to connect the ends of sections of submersible grounding electrodes with less labor-intensive and simple direct butt welding, without couplings. However, connection with couplings is more reliable and makes work easier. But couplings create additional resistance (increase the reaction of the soil), slow down the dive slightly and reduce the maximum possible dive depth for a given mechanism power, which is especially noticeable in dense soil. Butt welding still cannot be recommended, since it is fragile, and welding with an overlap or with overlays slows down the immersion even more than a coupling.

For electrical safety, the hammer must have double insulation, or (with conventional insulation) it must be grounded by a separate core of the hose cable, through the remaining cores of which electricity is supplied from a generator or from an external network. An additional safety measure, as for working with any power tool, may be the use of rubber gloves or residual current devices.

If there is a compressor nearby, then instead of an electric hammer it is more rational to use a lightweight pneumatic hammer, but even then you need to have strong, stable sawhorses, since the pneumatic hammer in commonly used devices has to be held by hand during operation so that it does not jump off the electrode due to recoil. One of these devices is a special adapter attachment, the upper end is fixed in the pneumatic hammer and has a hollow cylinder at the lower end into which the end of the electrode is inserted.

The frame of the trestle can be made from thin-walled steel pipes with a diameter of 22-24 mm or from light but expensive duralumin pipes with a diameter of 20-22 mm, and the platform from boards 40 mm thick or from corrugated steel 4 mm thick. If the trestles are made entirely of boards, they will be heavier than steel ones and will quickly become unusable.

If there is no goat, then the electrode can be driven directly from the ground), but then the sections to be driven will have to be driven not 2.5 mm in length, as previously recommended, but shorter, in accordance with the height of the worker who will hold the power tool on the electrode.

Long (up to 5 m) electrodes of small diameter (up to 13 mm) can be driven into soft soil with an electric hammer without first preparing short sections and welding them on site. This greatly simplifies the work (Fig. 1, f).

The electric hammer is equipped with a clamp that acts when there is downward pressure on it and releases the electrode when the hammer is lifted. In addition, a guide angle is attached to the hammer. The electrode is passed through the clamp and through the hole in the guide angle. Then the device together with the electrode is placed on the ground and the electrode is immersed approximately 0.8 m. After the device approaches the ground, it is moved up the electrode to a height convenient for the worker and the driving of the ground electrode is continued.

If the power of the electric hammer is sufficient (0.6-0.8 kW), there is no need to prepare the end of the electrode for immersion, but with less power, the end of the electrode is sharpened to facilitate driving. Electric tools and mechanisms with an electric drive receive power from electric generators installed on cars and tractors or from small (2 kW) commercially produced gas-electric units transported in the bodies of cars.

If you have an electric rammer, then it can be used to drive in electrodes by removing the shoe designed for compacting soil and placing an impact sleeve on the striker, which has an internal diameter corresponding to the diameter of the rod electrode inserted into the sleeve. Similarly, electric hammer drills, electric concrete breakers and other electric or pneumatic manual impact machines can be adapted by equipping them with adapters for driving electrodes made of round steel or steel of other profiles.

When using pneumatic tools, compressed air is supplied from compressors, which can be electrically driven or mechanically driven from a car or tractor engine. One of the mechanical drive designs is shown in Fig. 5. On a T-40 (or other brand) tractor, install a compressor with a capacity of about 1 m3/min at an operating air pressure of up to 1 mPa. For air cooling, an automobile-type fan impeller is mounted on a spring. A gear is installed near the compressor to drive it from the tractor power take-off shaft.

Fig. 2. Pneumatic electrode plunger on the T-40 tractor with a trolley: 1 - dispensing valve; 2 - pressure gauge; 3 - pressure reducing valve; 4 - tractor; 5 - trailed trolley; 6 — transportable electrodes; 7 - compressor; 8 - gearbox; 9 — receiver; 10 - jackhammer; 11 - compressed air hose

A U-shaped receiver with a capacity of 300 liters, made, for example, from a seamless steel pipe with a diameter of 180 mm, is mounted in front of the tractor. Safety valves, a pressure gauge, a reducer for adjusting the compressed air pressure at the inlet and distribution valves for connecting hoses feeding pneumatic tools are installed on the receiver. A trailed trolley can be used to transport grounding electrodes, tools and equipment. Pneumatic tools (perforators, jackhammers, chipping hammers) are selected so that their characteristics correspond to the parameters of the compressor. When driving electrodes with mechanized tools (hand machines) of low power in the cold season, you need to have with you, in addition to the main device, a drill with long drills equipped with carbide tips. If the thickness of the frozen soil layer cannot be punched, it is drilled to the thawed soil, an electrode is inserted into the hole and driving continues.

During the construction of a 500 kV overhead line, employees of the Energostroymekhanizatsiya company group, together with employees of mechanized column No. 71 and Normative Research Station No. 40 Energostroytrud, proposed and implemented a unit for installing grounding devices for line supports. For this purpose, attachments were installed on the base of the DT-75 tractor, which included: a Zif-55 compressor; welding unit GS-300, hammer MO-5 with a set of hoses, adapter (striker) for driving in electrodes.

The work was carried out by two electric linemen and a tractor driver. On average, depending on the soil resistance, 4-5 electrodes 3-6 m long were driven from round steel with a diameter of 16 mm to ground each support. After driving the first three electrodes and welding horizontal jumpers to them, the resistance to the spreading of the grounding current was measured and, if necessary, additional electrodes were driven. The total time for constructing the grounding device of the support was about 2 hours.

The high productivity of the unit, which made it possible to use deep electrodes, gave reason to propose replacing the previously designed horizontal grounding beams with vertical ones, thereby achieving cost savings and halving metal consumption.

Factories have produced special machines for installing grounding devices and universal machines that can be used for this purpose.

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The most common mistakes of a manager

The main cause of errors that occur during grounding is ignoring the problems of galvanic corrosion and the associated incorrect selection of grounding system components, especially those used when connecting grounding electrodes. They most often occur when the grounding system deviates from its uniform classical shape. For example, in the case of an incomplete rim, with a tip in the form of vertical grounding electrodes, as well as in the case of connecting grounding and ring grounding electrodes. However, we would like to remind you that in the case of single-family houses (protection level III or IV), there is no need to increase, for example, the ring grounding electrode to obtain a certain grounding resistance.

Different metals placed in moist soil or concrete, that is, in an electrolytic environment, assume different electrical potentials measured relative to the reference electrode. Connected together, they form a galvanic cell through which a direct current can constantly flow as a result of a potential difference. Even if the value of this current is relatively small, on the order of milliamps, it is a dangerous phenomenon because it lasts continuously and causes accelerated degradation of the material from which the connection is made. In extreme cases, it completely collapses after a few years.