HOW TO MAKE GROUNDING

HOW TO MAKE GROUNDINGMy story will consist of three parts.
1 part. Grounding system (General information, terms and definitions).
Part 2. Traditional methods of construction of grounding devices (description, calculation, installation).
Part 3. Modern methods of construction of grounding devices (description, calculation, installation).

In the first part (theory) I will describe the terminology, principal grounding (purposes) and requirements for grounding requirements.
In the second part (practice) is the story of traditional solutions used in the construction of grounding devices, listing the advantages and disadvantages of these solutions.
The third part (practice) in a sense will continue the second. It will contain the description of new technologies used in the construction of grounding devices. As in the second part, listing the advantages and disadvantages of these technologies.

If the reader has theoretical knowledge and is interested only in the practical implementation — it is better to skip the first part and start reading with the second part.

If the reader has the necessary knowledge and wants to meet new products — it is better to skip the first two parts and go directly to reading the third.

My opinion on the described techniques and solutions in some extent one-sided. I ask the reader to understand that I’m not making your stuff for the comprehensive objective work and Express their point of view, your experience.

Some of the text is a compromise between accuracy and the desire to explain “human language”, so admitted simplification, which “cut the ear” tech-savvy reader.

1 part. Ground
In this part I will talk about terminology, about the main types of grounding and about the quality characteristics of grounding devices.

A. Terms and definitions
B. the Purpose (types) of grounding
B1. The working (functional) grounding
B2. Protective earth
B2.1. The ground, composed of external lightning protection
B2.2. Grounding as part of a system of surge protection (SPD)
B2.3. Grounding in the structure of the grid
V. As the ground. The resistance of the ground.
B1. Factors affecting the quality of ground
B1.1. The contact area of the grounding conductor with the ground
B1.2. The electrical resistance of the soil (specific)
B2. The existing standards for ground resistance
B3. Calculation of ground resistance

A. Terms and definitions
To avoid confusion and misunderstanding in the future, the story will begin with this item.
I will give a set of definitions from the current document “regulations for Electrical installation (PUE)” in the latest edition (Chapter 1.7 in edition of seventh edition).
And try to “translate” these definitions into “plain” language.

Grounding — deliberate electrical connection of any point of the network, installations or equipment to the grounding device (PUE 1.7.28).
Soil is the medium that has the ability to “soak up” the electricity. He also be a “General” point in the circuit, relative to which the perceived signal.

Grounding connection — a set of grounding/ earthing and grounding conductors (PUE 1.7.19).
This device/ circuit, consisting of a grounding conductor and a grounding conductor connecting the grounding conductor with the grounding part of the network, installations or equipment. Can be distributed, i.e. consist of several mutually remote earthing.

In the picture it is shown with thick red lines:

 

Grounding device

The grounding — a conducting part or aggregate of interconnected conductive parts located in electrical contact with the ground (PUE 1.7.15).
The conductive part is a metallic (conductive) element/ the electrode of any profile and a construction (pin, pipe, strip, plate, grid, a bucket : -), etc.) in the soil and through which it “flows” of electrical current from electrical installations.
Configuration of the earthing switch (number, length, arrangement of the electrodes) depends on the requirements imposed on him or her, and the ability of soil to “absorb” the electricity running the “flowing” of electrical installations via these electrodes.

In the figure it is shown with thick red lines:

 

Earthing

The earthing resistance is the ratio of the voltage on the grounding device to the current flowing in the earth electrode in the ground (RB 1.7.26).
Resistance of grounding — the main indicator of the grounding device, which determines its ability to perform its functions and determines its overall quality.
The earthing resistance depends on the area of electrical contact of the grounding conductor (grounding electrode) ground (“off” current) and the electrical resistivity of the soil in which is mounted the grounding (“absorption” current).

Grounding electrode (earthing electrode) — a conducting part which is in electric contact with a local ground (GOST R 50571.21-2000 p. 3.21)
I repeat: as the conductive parts may be metal (conductive) element of any profile and a construction (pin, pipe, strip, plate, grid, a bucket : -), etc.) in the soil and through which it “flows” of electrical current from electrical installations.

The figure they are shown as thick red lines:

 

Grounding electrode (earthing electrode)

Further definition not found or not described accurately enough in the standards and norms, so having only my description.

Ground loop — “national” title earthing or earthing devices, consisting of multiple grounding electrodes (electrode group) that are connected to each other and assembled around the object by its perimeter/ contour.

In the figure, the object is marked by gray square in the center
and the ground loop — the thick red lines:

 

Ground loop

Electrical resistivity of soil is a parameter that determines the degree to which the “conductivity” of the soil as a conductor, that is, how well it will spread in such an environment, the electric current from the grounding electrode.
This measured value is dependent on soil composition, size and density
fit to each other of the particles, humidity and temperature, concentration of soluble chemicals (salts, acid and alkaline residue).

B. the Purpose (types) of grounding
The ground is divided into two main types according to their role on the working (functional) and protective. Various sources provide additional types, such as: “instrumental”, “measuring”, “control”, “radio”.

B1. The working (functional) grounding
This is the grounding point or points of current carrying parts of the electrical installation to be performed to ensure operation of the installation (non-electrical) (EIC 1.7.30).

Working ground (electrical ground contact) is used for the normal functioning of the electrical installation or equipment, ie to work in NORMAL mode.

B2. Protective earth
This grounding is performed for electrical (PUE 1.7.29).

Protective grounding provides protection of the electrical installation and equipment, as well as protecting people from exposure to hazardous voltages and currents which may arise in cases of failure, incorrect operation of equipment (i.e., EMERGENCY mode) and lightning.
Protective grounding is used to protect equipment from interference when switching in the supply network and interface circuits, as well as from electromagnetic interference induced from nearby equipment.

Read more a protective purpose of the grounding can be seen in two examples:
as part of the external molniezaschita system in the form of grounded lightning
as part of a system of surge protectors
in the structure of the grid object

B2.1. Grounding in the composition of lightning protection
Lightning is the discharge or “breakdown” that occurs FROM cloud To ground, with the accumulation of a cloud of charge critical value (relative to the earth). Examples of this phenomenon on a smaller scale is a “breakdown” in the condenser and gas discharge in the lamp.

The air is an environment with a very high resistance (insulator), category but overcomes it, because great in power. The discharge path passes through areas of least resistance, like water drops in the air and trees. This explains the root-like outgrowths branching structure of lightning in the air and frequent lightning strikes to trees and buildings (they have less resistance than the air in between).
When injected into the roof of the building, the lightning continues on its path to the ground, choosing sites with the least resistance: damp walls, wires, pipes, appliances — thus presenting a danger to humans and equipment located in this building.

Lightning protection is designed to divert the lightning from the protected building/ object. Lightning follows the path of least resistance falls in a metal lightning on the object, then the metal lightning rods located on the outside of the object (e.g., walls), descends to the ground, where it diverges (remember: soil is the medium that has the ability to “absorb” the electricity).

In order to make the system “attractive” to lightning, and also to prevent the spread of lightning currents from parts (receiver and bends) inside the object, its connection with the ground is carried through the grounding with a low grounding resistance.

 

grounding with low resistance grounding

Grounding in such a system is required, as it provides a complete and rapid transition of the lightning currents in the soil, preventing their spread throughout the object.

B2.2. Grounding as part of a system of surge protectors (SPD)
SPD is designed to protect electronic equipment from a charge accumulated on any land line/network as a result of exposure to electromagnetic fields (EMFs) induced from standing next to powerful electrical installations (or high-voltage lines) or EMFs encountered in close (up to hundreds of meters) lightning discharge.

A striking example of this phenomenon is the accumulation of charge on the copper cable network or the house on the “forwarding” between buildings during a thunderstorm. At some point, the devices connected to this cable (the computer’s network card or switch port), can not stand the “size” of the accumulated charge and electric breakdown occurs inside the device, destroying it (simplified).
To “bleed” the accumulated charge in parallel “load” on the line before the equipment puts SPD.

Classic SPD is a gas arrestor designed for a certain “threshold” of charge that is less than the “margin of safety” of the protected equipment. One of the electrodes of this spark gap is grounded and the other connected to one of the wires of the line/ cable.

When this threshold is reached within the spark gap discharge occurs 🙂 between the electrodes. Causing the stored charge is discharged to the ground (through ground).

 

Classic SPD

As in lightning protection — grounding in such a system is required, as it provides timely and guaranteed the appearance of the discharge in the SPD, avoiding the excess charge on the line above is safe for the protected equipment level.

B2.3. Grounding in the structure of the grid
A third example of the protective role of grounding is to ensure the safety of man and equipment in cases of failure/ accident.

The easiest such failure is described by the circuit of phase wire of mains supply to housing (short in the power supply or a short in the heater via the aquatic environment). The man that touched such a device will create electrical circuit through which current is run, causing in the body damage to internal organs, primarily the nervous system and heart.

To eliminate such effects the connection of the buildings with the ground connection (for removal of emergency currents in the ground) and automatic protective device for a split second turns off the current in emergencies.

For example, grounding all enclosures, cabinets and racks of telecommunications equipment.

 

Grounding all enclosures, cabinets and racks of telecommunications equipment

V. As the ground. The resistance of the ground.
To correctly perform grounding of its functions it must have certain parameters/ characteristics. One of the main properties determining the quality of ground, is the resistance to current spreading (resistance grounding) indicating the ability of the grounding conductor (grounding electrode) to transfer the currents received from the equipment into the ground.
This resistance has a finite value and in the ideal case is a zero value that means the absence of any resistance by passing “harmful” currents (this ensures FULL absorption by the soil).

B1. Factors affecting the quality of ground
The resistance depends mainly on two conditions:
area ( S ) of electrical contact of the ground conductor with the ground
electrical resistance ( R ) of the soil in which the electrodes are

 

Factors influencing the quality of the ground

B1.1. The contact area of the grounding conductor with a ground.
The greater the contact area of ground soil, the more area for the transition of current from earthing to the ground (the more favorable conditions are created to transfer current into the ground). This can be compared with the behavior of a vehicle wheel on the turn. A narrow tire has a small contact area with the asphalt and can easily start to slide on him, “sending” the car into a skid. A wide tire, but still a little deflated, has a much larger contact area with the asphalt, providing a secure grip with him and, therefore, reliable controls.

To increase the area of contact of the earthing switch with the soil or increasing the number of electrodes, joining them together (adding the area of several electrodes) or by increasing the size of the electrodes. In the application of vertical ground electrodes the latter method is very effective if deep layers of soil have lower electrical resistance than the top.

B1.2. The electrical resistance of the soil (specific)
Let me remind you: this is the quantity that determines how well the soil conducts current through itself. The smaller resistance will have the soil, the better/ easier it will be to “absorb” the current from earthing.

Examples of soils, well-conductive is salt marshes or wet clay. The perfect natural environment for passing a current of sea water.
An example of “bad” to ground the soil is dry sand.
(If interested, you can see a table of values of specific resistance of soilused for calculation of grounding devices).

Returning to the first factor and method of reducing earth resistance in the form of increasing the depth of the electrode, we can say that in practice more than in 70% of cases the soil at a depth of 5 meters has significantly less resistivity than the surface, due to the greater humidity and density. Often groundwater, which provide the ground a very low resistance. Grounding in such cases is very high quality and reliable.

B2. The existing standards for ground resistance
Since the ideal (zero-resistance spreading) is impossible to achieve all electrical and electronic devices are created from some of the normalized values of ground resistance, for example 0.5, 2, 4, 8, 10, 30 and more Ohms.

For orientation will result in the following values:
for substation with voltage of 110 kV resistance to spreading currents should be less than 0.5 Ohm (PUE 1.7.90)
when connecting telecommunications equipment, grounding should typically have a resistance of less than 2 or 4 Ohms
for reliable operation of the gas arresters in the protection devices of air-lines of communication (for example, a local network based on copper cable or RF cable) the resistance of the ground to which they (the arrestors) are connected should be less than 2 Ohms. There are instances of requirement in 4 Ohms.
the current source (e.g. a transformer substation) grounding resistance should be less than 4 Ohms for linear voltage of 380 V three-phase source current or 220 V single-phase source current (EIC 1.7.101)
the ground used for connection of lightning, the resistance should be 10 Ohms (RD 34.21.122-87, p. 8)
for private houses, with connection to mains 220 Volt / 380 Volt:
when using the system TN-C-S necessary to have local grounding with the recommended resistance not exceeding 30 Ohms (guided by PUE 1.7.103)
when using the TT (isolate ground from neutral source current) and applying current devices (RCD) with trip current of 100 mA is necessary to have local grounding with a resistance less than 500 Ohms (PUE 1.7.59)

B3. Calculation of ground resistance
For the successful design of the ground device having the ground resistance, are usually used, a typical configuration of earthing and basic formulas for calculations.

The configuration of the grounding conductor is usually chosen by the engineer based on his experience and the possibilities of its (configuration) application on a particular object.

The choice of formulas depends on the chosen configuration of the grounding.
The formulae contain parameters of this configuration (e.g. number of earthing electrodes, their length, thickness) and the parameters of soil of a particular object that will host the grounding. For example, for a single vertical electrode, the formula would be:

 

Choice formulas

The accuracy of the calculation is usually low and depends again on the ground — in practice the differences of practical results is found in almost 100% of cases. This is due to its (soil) large heterogeneity: it varies not only in depth but also in size, forming a three-dimensional structure. The existing formulas for calculating the parameters of the ground are struggling to cope with one-dimensional heterogeneity of the soil, and the calculation in the three-dimensional structure is associated with enormous computational power and requires very high operator training.
In addition, to create accurate maps of soil is necessary to produce a large amount of geological work (for example, for a square of 10 x 10 meters is necessary to make and perform about 100 boreholes up to 10 metres), which causes a significant increase in the cost of the project and often not possible.

In light of the above almost always calculation is required, but an estimated measure, and is usually conducted on the principle of achieve earth resistance “not more than”. In the formula substitute the average values of the soil resistivity, or its maximum value. This provides a “margin of safety” and in practice expressed in obviously lower (lower is better) values of ground resistance than expected in the design.

Construction of earthing
During the construction of the earthing switches are most commonly used for vertical grounding electrode. This is due to the fact that the horizontal electrodes are difficult to bury in great depth, and with shallow depth of these electrodes — they are very greatly increases the resistance of the ground (the deterioration of the main characteristics) in the winter due to freezing of the upper soil layer, causing a large increase in its electrical resistivity.

As the vertical electrodes almost always choose the steel pipe, pins/ rods, angles, etc. standard rolling products that have a long (over 1 meter) with relatively small transverse dimensions. This choice is connected with the possibility of easy penetration of such elements into the ground in contrast to, for example, from a flat sheet.

Read more about construction in the following sections.

Alex Rogankov, technical specialist.

In the preparation of this article used the following materials:
Regulations for Electrical installation (PUE), part 1.7 in edition of seventh edition
GOST R 50571.21-2000 (IEC 60364-5-548-96)
The grounding device and system of equalization of electrical potentials in electrical installations containing equipment information processing (Google)
Instruction on installation of lightning protection of buildings and facilities RD 34.21.122-87
Publication on the site “Ground to ZANDZ.ru
Own experience and knowledge

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