Smart poles system

Earthing is one of the most common things done not only for protection purposes in a power system but also for measurement purposes. In electrical engineering, ground or earth can refer to a common return path for electric current, a reference point in an electrical circuit or a direct physical conn

Project Title

Smart poles system

Project Area of Specialization

Electrical/Electronic Engineering

Project Summary

Earthing is one of the most common things done not only for protection purposes in a power system but also for measurement purposes. In electrical engineering, ground or earth can refer to a common return path for electric current, a reference point in an electrical circuit or a direct physical connection to the Earth.For effective protection of a system by earthing, the earth resistance value must be within a precise range. Hence, installation of earthing system must be meticulously done. The earth resistance depends on the earth electrode as well as the soil surrounding it. Our project is basically on the factors affecting the resistance of an earthing system, measurement of earth resistance and the construction process of an earth pit.

Project Objectives

Earthing serves its purpose only if its resistance is within a precise range of values and this value is in general made as low as possible to provide an easier path for current flow during abnormalities. For example, consider earthing done for protecting people who handle an equipment. In a properly earthed system, when a live conductor comes in contact with a metallic part due to insulation failure, the current will flow through the earth conductor and not through the human body when a person touches the metallic part accidentally. If the earth resistance is high, the human body would be the lower resistance path for current flow and the purpose of earthing is lost. Furthermore, a potential difference between the grounding electrode and a distant reference point is created because of the current injected into the earth through the grounding electrode and the earth’s resistance is also nonzero. This potential rise can cause hazards. In general, the maximum allowable resistance is around 5 ohms for one earth electrode and 1 ohm for the total earthing system which includes all the earth electrodes connected in parallel.

There are a myriad of uses and advantages of earthing a system. Some of them are:

1. The magnitude of transient over-voltages is reduced .
2.  Locating ground fault is simplified .
3.  Improved fault protection for a system or equipment .
4.  Greater safety of operating person and reduce risk and probability of injuries or accidents .
5.  Improved lightning protection .

Project Implementation Method

EARTH PIT LOCATION :

Dry sand, gravel chalk, limestone, granite and any very stony ground should be avoided while selecting a location for constructing an earth pit.A site should be chosen that is not naturally well-drained. A water-logged location is not essential, unless the soil is sand or gravel. In general, there is no advantage with increase in moisture content above 15 to 20 percent as explained previously. Care should be taken to avoid a site which is kept moist by water flowing over it (for example, by a stream of water) as the beneficial salts may be entirely washed away from the soil.

ELECTRODE MATERIAL:

Electrode material does not affect initial earth resistance significantly. Appropriate precautions need to be taken while selecting the material so that it is resistant to corrosion in the type of soil in which it will be used. Tests in a wide variety of soils have shown that copper, whether tinned or not, is more suitable compared to ferrous materials (for example, cast iron, wrought iron or mild steel). Galvanized mild steel is also observed to be a little inferior to copper in this regard. While selecting and designing earth electrode, care should be taken regarding the thermal rating of the electrode. The electrode must be able to withstand the heat produced due to current flow (current density) through it.

MEASURING EARTH RESISTANCE:

Soil resistivity varies more with depth compared to its variation with horizontal distances. Stratification of earth layers is the main reason for variation in resistivity with depth. Homogeneity of the soil can be identified from the resistivity measurements. If the soil is uniform, conventional methods are used to calculate earth resistivity. When the soil is non-uniform, either a gradual variation or a two-layer model is used for computing earth resistivity.

COMPONENTS OF RESISTANCE OF AN EARTHING SYSTEM:

a) Resistance of the (metal) electrode

b) Contact resistance between the soil and the electrode

c) Resistance of the soil from the electrode surface in the direction of flow of current outward from the electrode to infinite earth. The major contributing factor to earthing resistance is the soil resistance whereas the other two factors are small fractions of an ohm and can be neglected for all practical purposes.

Benefits of the Project

 BENEFITS OF THE PROJECT:

1.   As a safety feature for property, equipment and life:

An earthed circuit reduces the risk of death or injury by providing an alternate path for current to discharge into the ground. Equipment, appliances and property are protected against faults, leaks and fires resulting from short-circuits and sparking.

2.      Protection against over-voltage:

Earthing also provides protection against power surges, accidental connection with high-voltage lines and even lightning strikes, allowing the energy to flow to the ground, with minimal effect.

3.      Voltage Stabilisation :

The ground offers a common point of reference for calculating the relationship between different voltage sources. It's been used as a universal standard since the introduction of the distribution system.

Technical Details of Final Deliverable

Earth pit is a pit in which connection is made between earthing electrodes that have been placed inside the soil and the earthing conductor that connects the electrical installation. The following is an overview of the construction procedure of an earth pit and may vary from country to country according to the standards followed in that country. The rating of Galvanized Iron (GI) plate, size of pit, materials used to fill the pit etc. will vary depending on various factors which have been explained before. The following procedure is generally followed in Pakistan.

1. Excavate a pit to place the plate electrode.
2. Use a GI plate of appropriate size according to required resistance value and the standard followed in that country. This GI plate is the Earth Plate.
3. ? Make a mixture of wood, coal powder, salt and sand (all in equal proportions and amount depends on size of pit). This mixture is a good conductor of electricity and also serves as an anti-corrosive, hence ensuring longer life of the GI plate. Coal absorbs water and keeps the soil wet. Furthermore, coal is made up of carbon which is a good conductor, hence it minimizes earth resistance. Salt helps in forming electrolyte which increases the conductivity between the GI Plate and Earth. Sand, which is porous in nature helps to circulate water and humidity around the mixture. 
4. Put the GI Plate(Earth Plate) in the middle of the mixture inside the pit
5. Use a GI strip to connect the GI Plate to the System Earthing. It is better to use a GI Pipe with a flange on the top to cover the GI strip from Earth plate to the top flange.
6. The top of the pipe is covered to prevent jamming of dust and mud.
7. For the purpose of maintaining moisture content in the soil surrounding the electrode, place another GI pipe with holes in different directions along its length such that the top of the pipe is at earth surface level. This pipe is placed adjacent to the set up. Water is poured at regular intervals using a funnel at the top to maintain the required moisture content in the soil and hence, ensure the required low resistivity of the soil. Care should be taken by watering the earth pit in summer so that the soil is wet and the earth resistance value is maintained.

Final Deliverable of the Project

HW/SW integrated system

Core Industry

Others

Other Industries

Security

Core Technology

Others

Other Technologies

Sustainable Development Goals

Responsible Consumption and Production, Climate Action

Required Resources

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