What is Electrical Earthing
Electrical Earthing can be defined as the process of transferring the immediate discharge of the electrical energy directly to the Earth with the help of the low-resistance wire. The electrical earthing is carried out by connecting the non-current-carrying part of the equipment or the neutral part of the supply system to the ground.
Importance of Earthing
Earthing, also known as grounding, is a fundamental and essential part of an electrical system. Despite not being a visible element, the earthing system is of vital importance for the safety of people and equipment. The earthing is essential because of the following reasons
- To save humans life from danger of electric shock or death by blowing a fuse i.e. to provide alternative path for the fault current to flow so that it will not endanger the user.
- To protect the building, machinery and appliances under fault conditions.
- To ensure that all the exposed conductive parts do not reach a dangerous potential.
- To provide safe path to lighting and short circuit currents
- To provide stable platform for operation of sensitive electronic equipments i.e. to maintain the voltage at any part of electrical system at a know value so as to prevent over current or excessive voltage on the appliances or equipment.
- lighting line surges or unintentional contact with higher voltage lines can cause dangerously high voltages to the electrical distribution system. Earthing provides the alternative path around the electrical system to minimize damages in the system.
- There are many sources of electricity. Every transformer can be considered a separate source. if there were not a common reference point for all these voltages sources it would be extremely difficult to calculate their relationship to each other.
Difference Between Grounding and Eathing
Earthing and grounding are similar terms. Still, these are having many differences.One of the major difference between the grounding and the earthing is that in grounding, the current carrying part is connected to the ground whereas in earthing the non-current carrying parts is connected to ground.
|1||The current carrying part is connected to ground.||The body of the equipment is connected to ground.|
|2||Between the neutral of the equipment and ground||Between the equipment body and earth pit which is placed under the earth surface.|
|3||Does not have zero potential||Have zero potential|
|4||It provides Protection to the power system equipment.||It provides protection to the human from electric shock.|
|5||It Provide the return path to the current.||It discharges the electrical energy to the earth.|
|6||There are Three types of Grounding (Solid, Resistance and Reactance grounding)||There are five types of earthing (Pipe, Plate, Rod earthing, earthing through tap and strip earthing)|
|7||It is used for balancing the unbalance load.||It is used for avoiding the electrical shock.|
|8||The examples are Neutral of generator and power transformer is connected to ground.||The examples are The enclosure of the transformer, generator, motor etc. are connected to the earth.|
Types of Electrical Earthing
There are two types of Electrical Earthing
- System or neutral Earthing
- Equipment Earthing
System or neutral Earthing: All power systems of today operate with grounded neutrals. The neutral of the system is directly connected to earth by the help of the GI wire/ GI Strip. The neutral grounding is an important aspect of power system design because the performance of the system regarding short circuits, stability, protection, etc., is greatly affected by the condition of the neutral.
Some of the advantages of neutral Earthing are as follows
- Voltages of phases are limited to the line-to-ground voltages.
- Surge voltage due to arcing grounds is eliminated.
- The overvoltage’s due to lightning discharged to ground.
- It provides greater safety to personnel and equipment.
- It provides improved service reliability.
Equipment Earthing: It is different from neutral point Earthing. Equipment Earthing means connecting the non-current carrying metallic parts in the neighbouring of electrical circuits to earth. The non-current carrying parts include the following.
- Motor body, Switchgear metal enclosure, transformer tank, conduits of wiring etc.
- Support structures, tower, poles
- Sheets and cables
- Body of portable equipment such as electric iron, drill, trolley
Various Methods of Earthing
The various methods of Earthing are discussed below
- 300Plate Earthing: – In this method an earthing plate either of copper of dimension 60cm×60cm×3m or of galvanized iron of dimensions 60 cm× 60 cm×6 mm is buried into the ground vertical at a depth of not less than 3 meters from ground level. The earth plate is inserted with alternative layers of coke and salt. The earth wire (GI or copper wire) is tightly bolted to an earth plate with the help of nut or bolt.\\\;\;\;\;\;\;\;
- Pipe Earthing: – In this a galvanized steel and a perforated pipe of approved length and diameter is placed vertically in a wet soil. It is the most common system of earthing. The size of pipe to use depends on the magnitude of leakage current and the type of soil. The dimension of the pipe is usually 40mm (1.5in) in diameter and 2.75m (9ft) in length for ordinary soil or greater for dry and rocky soil. The moisture of the soil will determine the length of the pipe to be buried. The pipe is surrounded by small pieces of coke or charcoal. Alternate layers of coke and salt are used to increase the effective area of the earth and to decrease the earth resistance respectively. During summer the moisture in the soil decreases, which causes an increase in earth resistance. So a cement concrete work is done to keep the water arrangement accessible, and in summer to have an effective earth, 3 or 4 buckets of water are put through the funnel connected to pipe, which is further connected to GI pipe. \\\;\;\;\;\;\;\;
- Rod Earthing: – It is the same method as pipe earthing. A copper rod of 12.5mm (1/2 inch) diameter or 16mm (0.6in) diameter of galvanized steel of length above 2.5m (8.2 ft) are buried upright in the earth manually or with the help of a pneumatic hammer. The length of embedded electrodes in the soil reduces earth resistance to a desired value. \\\;\;\;\;\;\;\;
- Coil Earthing: – Earth wire is wound in the form of a coil of 50 mm dia. and 450 mm length (approx.) The surrounding space around the coil is filled up by 300 mm alternate layers of salt and coke/charcoal up to 1500 mm from the bottom. The top and surrounding remaining space of the pit is filled up with loose earth.\\\;\;\;\;\;\;\;
- Chemical Earthing: In this method a pipe contain earthing chemical is used. The earthing chemical – Bentonite and Marconite is used.\\\;\;\;\;\;\;\;
- Megger test | Transformer insulation resistance test
- why we don’t use wooden core in a transformer
- Why Transformer is Not Connected to DC Source