The main reason for the need for grounding in electrical networks is safety. When all metal parts of electrical equipment are grounded, then, even in the case of broken insulation, dangerous voltages will not be created on its case, they will be prevented by reliable grounding systems.
Tasks for grounding systems
The main tasks of security systems operating on the principle of grounding:
- Safety for human life, in order to protect against electric shock. Provides an alternate path for emergency current to avoid harming the user.
- Protecting buildings, machinery and equipment during power failure conditions so that exposed conductive parts of equipment do not reach lethal potential.
- Protection against overvoltage due to lightning strikes that can lead to dangerous high voltages in the electrical distribution system or from inadvertent human contact with high voltage lines.
- Voltage stabilization. There are many sources of electricity. Each transformer can be considered as a separate source. They must have a common negative reset point available.energy. The earth is the only such conductive surface for all energy sources, so it has been adopted as the universal standard for current and voltage shedding. Without such a common point, it would be extremely difficult to ensure security in the power system as a whole.
Ground system requirements:
- It must have an alternate path for dangerous current to flow.
- No dangerous potential on exposed conductive parts of the equipment.
- Must be low impedance enough to provide enough current through fuse to cut power (<0, 4 sec).
- Should have good corrosion resistance.
- Must be able to dissipate high short circuit current.
Description of grounding systems
The process of connecting the metal parts of electrical apparatus and equipment to the ground with a metal device that has little resistance is called grounding. When grounding, the current-carrying parts of the devices are directly connected to the ground. Grounding provides a return path for leakage current and therefore protects power system equipment from damage.
When a fault occurs in equipment, there is an imbalance of current in all three of its phases. Grounding discharges the fault current to ground and therefore restores the operating balance of the system. These defense systems have several advantages, such as eliminatingovervoltage through discharging it to ground. Grounding ensures equipment safety and improves service reliability.
Zeroing method
Grounding means connecting the bearing part of the equipment to the ground. When a fault occurs in the system, a dangerous potential is created on the outer surface of the equipment, and any person or animal accidentally touching the surface may receive an electric shock. Zeroing discharges dangerous currents to the ground and therefore neutralizes the current shock.
It also protects equipment from lightning strikes and provides a discharge path from surge arresters and other quenching devices. This is achieved by connecting parts of the plant to earth with a ground conductor or electrode in close contact with the soil, placed some distance below ground level.
The difference between grounding and grounding
One of the main differences between grounding and grounding is that when grounding, the carrying conductive part is connected to the ground, while when grounding, the surface of the devices is connected to the ground. Other differences between them are explained below in the form of a comparison table.
Comparison chart
| Basics for comparison | Grounding | Zeroing |
| Definition | Conductive part connected to ground | Equipment case connected to ground |
| Location | Between equipment neutral and ground | Between the equipment case and the ground, which is placed under the ground surface |
| Zero Potential | Does not have | Yes |
| Protection | Protect power grid equipment | Protect a person from electric shock |
| The path | The return path to the current ground is indicated | Discharges electrical energy to the ground |
| Types | Three (solid resistance) | Five (pipe, plate, electrode ground, ground and ground) |
| Wire color | Black | Green |
| Use | For load balancing | To prevent electric shock |
| Examples | Generator and power transformer neutral connected to earth | Casing of transformer, generator, motor, etc. connected to ground |
TN protective wires
These types of grounding systems have one or more directly grounded points from the power source. Exposed conductive parts of the installation are connected to these points using protective wires.
In the worldpractice, a two-letter code is used.
Used letters:
- T (French word Terre means "earth") - a direct connection of a point to the ground.
- I - no point connected to ground due to high impedance.
- N - direct connection to source neutral, which in turn is connected to earth.
Based on the combination of these three letters, there are types of grounding systems: TN, TN-S, TN-C, TN-CS. What does this mean?
In a TN earthing system, one of the source points (generator or transformer) is connected to earth. This point is usually the star point in a three-phase system. The chassis of the connected electrical device is connected to earth through this earth point on the source side.
In the picture above: PE - Acronym for Protective Earth is a conductor that connects exposed metal parts of a consumer's electrical installation to earth. N is called neutral. This is the conductor connecting the star in a three-phase system to earth. By these designations in the diagram, it is immediately clear which grounding system belongs to the TN system.
TN-S neutral line
This is a system that has separate neutral and protective conductors throughout the wiring diagram.
Protective conductor (PE) is the metallic sheath of the cable that feeds the installation or a single conductor.
All exposed conductive parts with the installation are connected to this protective conductor through the main terminal of the installation.
TN system-C-S
These are types of earthing systems in which neutral and protective functions are combined into one system conductor.
In the TN-CS neutral earthing system, also known as Protective Multiple Earthing, the PEN conductor is referred to as the combined neutral and earth conductor.
The PEN conductor of the power system is grounded at several points, and the ground electrode is located at or near the installation site of the consumer.
All exposed conductive parts to the unit are connected by a PEN conductor using the main earth terminal and neutral terminal and are connected to each other.
TT protection circuit
This is a protective earth system with a single power source point.
All exposed conductive parts with installation that are connected to the ground electrode are electrically independent of the ground source.
Insulating system IT
Protective earth system with no direct connection between live parts and earth.
All exposed conductive parts with installation that are connected to a ground electrode.
The source is either connected to ground through a deliberately introduced system impedance, or isolated from ground.
Designs of protective systems
Connection between electrical appliances and devices with a ground plate or electrode through a thick wire with low resistance to ensuresafety is called grounding or grounding.
The earthing or earthing system in the electrical network works as a safety measure to protect human life as well as equipment. The main purpose is to provide an alternative route for hazardous flows to avoid accidents due to electrical shock and equipment damage.
Metal parts of the equipment are grounded or connected to earth, and if for any reason the insulation of the equipment fails, high voltages that may be present in the external coating of the equipment will have a discharge path to earth. If the equipment is not grounded, this dangerous voltage can be transmitted to anyone who touches it, resulting in electric shock. The circuit is completed and the fuse is immediately activated if the live wire touches the earthed case.
There are several ways to perform the grounding system of electrical installations, such as grounding a wire or strip, plate or rod, grounding by grounding or through water supply. The most common methods are zeroing and insert setting.
Ground mat
A ground mat is made by connecting a number of rods through copper wires. This reduces the overall resistance of the circuit. These electrical grounding systems help limit ground potential. The ground mat is mainly used in the place where large current is to be testeddamage.
When designing an earth mat, the following requirements are taken into account:
- In the event of a malfunction, the voltage must not be dangerous to a person when touching the conductive surface of the equipment of the electrical system.
- The DC short circuit current that can flow into the ground mat must be quite large for the protection relay to work.
- The soil resistance is low so that leakage current can flow through it.
- The design of the ground mat should be such that the step voltage is less than the allowable value, which will depend on the soil resistivity required to isolate the faulty installation from humans and animals.
Electrode overcurrent protection
With this building grounding system, any wire, rod, pipe or bundle of conductors is placed horizontally or vertically in the ground next to the protective object. In distribution systems, the earth electrode may consist of a rod about 1 meter long and placed vertically in the ground. The substations are made using a ground mat, not individual rods.
Pipe current protection circuit
This is the most common and best electrical installation earthing system compared to other systems suitable for the same earth and moisture conditions. In this method, galvanized steel and a perforated pipe with a calculated length and diameter are placed vertically on constantly wet soil, asshown below. Pipe size depends on current current and soil type.
Typically, the pipe size for a house earthing system is 40 mm in diameter and 2.5 meters long for normal soil, or longer for dry and stony soil. The depth at which the pipe must be buried depends on the moisture content of the soil. Typically, the pipe is located 3.75 meters deep. The bottom of the pipe is surrounded by small pieces of coke or charcoal at a distance of about 15 cm.
Alternative levels of coal and s alt are used to increase the effective land area and thus reduce drag. Another pipe with a diameter of 19 mm and a minimum length of 1.25 meters is connected at the top of the GI pipe through a reducer. In summer, soil moisture decreases, which leads to an increase in earth resistance.
Thus, work is being carried out on a cement concrete base to keep water available in summer and to have land with the necessary protective parameters. Through a funnel connected to a pipe with a diameter of 19 mm, 3 or 4 buckets of water can be added. Either a GI ground wire or a strip of GI wire with sufficient cross-section to safely remove current is carried into a 12 mm diameter GI pipe at a depth of about 60 cm from the ground.
Plate earthing
In this earthing system device, the earthing plate of 60 cm × 60 cm × 3 m copper and 60 cm × 60 cm × 6 mm galvanized iron is immersed in the ground with a vertical surface at a depth of at least 3 m from ground level
The protective plate is inserted into the auxiliary layers of charcoal and s alt with a minimum thickness of 15 cm. The ground wire (GI or copper wire) is bolted tightly to the ground plate.
Copper plate and copper wire are not commonly used in protection circuits due to their higher cost.
Ground connection through water supply
In this type, the GI or copper wire is connected to the plumbing network with a steel bond wire that is attached to the copper lead as shown below.
The plumbing is made of metal and is located below the surface of the earth, i.e. directly connected to the ground. The flow of current through the GI or copper wire is directly grounded through the plumbing.
Calculation of ground loop resistance
Resistance of a single strip of a rod buried in the ground is:
R=100xρ / 2 × 3, 14 × L (loge (2 x L x L / W x t)), where:
ρ - soil stability (Ω ohm), L - strip or conductor length (cm), w - strip width or conductor diameter (cm), t - burial depth (cm).
Example: Calculate the resistance of the ground strip. Wire with a diameter of 36 mm and a length of 262 meters at a depth of 500 mm in the ground, the earth resistance is 65 ohms.
R is the resistance of the ground rod in W.
r - Ground resistance (Ohmmeter)=65 Ohm.
Measuring l - rod length (cm)=262 m=26200 cm.
d -rod inner diameter (cm)=36mm=3.6 cm.
h - hidden strip / rod depth (cm)=500 mm=50 cm.
Ground strip/conductor resistance (R)=ρ / 2 × 3, 14 x L (loge (2 x L x L / Wt))
Ground strip/conductor resistance (R)=65 / 2 × 3, 14 x 26200 x ln (2 x 26200 x 26200 / 3, 6 × 50)
Ground strip/conductor resistance (R) =1.7 Ohm.
The rule of thumb can be used to calculate the number of ground rod.
Approximate resistance of Rod / Pipe electrodes can be calculated using the resistance of rod/pipe electrodes:
R=K x ρ / L where:
ρ - earth resistance in Ohmmeter, L - electrode length in the meter, d - diameter of the electrode in the meter, K=0.75 if 25 <L / d <100.
K=1 if 100 <L / d <600.
K=1, 2 o / L if 600 <L / d <300.
Number of electrodes, if you find the formula R (d)=(1, 5 / N) x R, where:
R (d) - required resistance.
R - single electrode resistance
N - the number of electrodes installed in parallel at a distance of 3 to 4 meters.
Example: calculate the resistance of the ground pipe and the number of electrodes to obtain a resistance of 1 ohm, soil resistivity from ρ=40, length=2.5 meters, pipe diameter=38 mm.
L / d=2.5 / 0.038=65.78 so K=0.75.
Resistance of pipe electrodes R=K x ρ / L=0, 75 × 65, 78=12 Ω
One electrode - resistance - 12 Ohm.
To obtain a resistance of 1 ohm, the total number of electrodes required=(1.5 × 12) / 1=18
Factors affecting earth resistance
NEC code requires a minimum ground electrode length of 2.5 meters for ground contact. But there are some factors that affect the ground resistance of the protective system:
- Length/depth of ground electrode. Doubling the length reduces surface resistance by up to 40%.
- Ground electrode diameter. Doubling the diameter of the ground electrode reduces the ground resistance by only 10%.
- Number of ground electrodes. To improve efficiency, additional electrodes are installed at the depth of the main ground electrodes.
Construction of protective electrical systems of a residential building
Earth structures are currently the preferred method of grounding, especially for electrical networks. Electricity always follows the path of least resistance and diverts the maximum current from the circuit into ground pits designed to reduce resistance, ideally down to 1 ohm.
To achieve this goal:
- 1.5m x 1.5m area is dug to a depth of 3m. The hole is half-filled with a mixture of charcoal powder, sand and s alt.
- GI plate 500mm x 500mm x 10mm is placed in the middle.
- Establish connections between ground plate for private house grounding system.
- Otherpart of the pit is filled with a mixture of coal, sand, s alt.
- Two 30mm x 10mm GI strips can be used to connect the ground plate to the surface, but a 2.5" GI pipe with a flange at the top is preferred.
- In addition, the top of the pipe can be covered with a special device to prevent dirt and dust from entering and clogging the earth pipe.
Installation of the grounding system and benefits:
- Charcoal powder is an excellent conductor and prevents corrosion of metal parts.
- S alt dissolves in water, greatly increasing conductivity.
- Sand allows water to pass through the hole.
To check the efficiency of the pit, make sure that the voltage difference between the pit and the mains neutral is less than 2 volts.
Pit resistance must be maintained at less than 1 ohm, distance up to 15 m from the protective conductor.
Electric shock
Electric shock (electroshock) occurs when two parts of a person's body come into contact with electrical conductors in a circuit that has different potentials and creates a potential difference throughout the body. The human body has resistance, and when it is connected between two conductors at different potential, a circuit is formed through the body and current will flow. When a person contacts only one conductor, no circuit is formed and nothing happens. When a person comes into contact with the conductors of the circuit, no matter what voltage is in it, alwaysthere is a possibility of electric shock injury.
Lightning risk assessment for residential buildings
Some homes are more likely to attract lightning than others. They increase depending on the height of the building and proximity to other houses. Proximity is defined as three times the distance from the height of the house.
In order to determine how vulnerable a residential building is to lightning strikes, you can use the following data:
- Low risk. One-level private residences in close proximity to other houses of the same height.
- Medium risk. A two-level private house surrounded by houses with similar heights or surrounded by houses of lower heights.
- High risk. Isolated houses that are not surrounded by other structures, two-story houses or houses with a lower height.
Regardless of the likelihood of a lightning strike, the correct use of important lightning protection components will help protect any residential building from such damage. Lightning protection and grounding systems are required in a residential building so that the lightning strike is diverted to the ground. The system typically includes a ground rod with a copper connection that is installed in the ground.
When installing a lightning protection scheme in a house, please follow the following requirements:
- Ground electrodes must be at least half 12mm long and 2.5m long.
- Copper connections recommended.
- If the system site has rocky soil or engineering underground lines, it is prohibited to usevertical electrode, only the horizontal conductor is needed.
- It must be recessed at least 50cm from the ground and extend at least 2.5m from the house.
- Private home grounding systems must be interconnected using the same size conductor.
- Connectors for all underground metal piping systems, such as water or gas pipes, must be located within 8m of the home.
- If all systems were already connected before lightning protection was installed, all that is required is to tie the nearest electrode to the plumbing system.
All people living or working in residential, public buildings are constantly in close contact with electrical systems and equipment and must be reliably protected from dangerous phenomena that may arise due to short circuits or very high voltages from a lightning discharge.
To achieve this protection, electrical network earthing systems must be designed and installed in accordance with standard national requirements. With the development of electrical materials, the requirements for the reliability of protective devices are increasing.
