Definition:The method of connecting noncurrent carrying parts of the electrical equipment or the neutral point of the supply system to the earth through the wire having negligible resistance is called electrical earthing. Earthing protects the electrical equipment from lightning strokes and earth fault conditions. It provides the easiest path to the fault or leakage current to flow through it.
Types of Electrical Earthing
The electrical equipment mainly consists of two non-current carrying parts. These parts are neutral of the system or frame of the electrical equipment. On the basis of the earthing of these two noncurrent carrying parts of the electrical system earthing can be classified into two types.
- Neutral Earthing
- Equipment Earthing.
Neutral earthing is defined as the earthing of the system neutral to ensure system security and protection. Neutral earthing is called the system earthing. In neutral earthing, the neutral point of the star-connected 3-phase windings of power transformers, generators, motors, the earthing transformer is connected to the low resistance.
Equipment earthing deals with the earthing of noncurrent carrying parts (frame or metallic body) of the electrical equipment to ensure the safety of personnel and protecting against lightning. It also helps in earth fault protection.
Importance of Earthing
The earthing is essential because of the following reasons
- Earthing provides the safety of the personnel from the electric shock. It insures that the non-currents carrying parts, such as equipment frames are always safe at ground potential even though the insulation fails.
- Earthing is essential for the safety of the equipment and personnel against lightning and voltage surges, providing the discharge path for surge arrestors, gaps, and other similar devices.
- It provides the ground connections for the ground neutral system.
- It provides a means of positively discharging and de-energizing feeders or equipment before proceeding with maintenance on them.
Earthing can be done by electrically connecting the respective parts in the installation to some system of electrical conductors or electrodes placed near the soil or below the ground level. The earthing mat or electrode under the ground level have flat iron riser through which all the non-current-carrying metallic parts of the equipment are connected.
When the fault occurs the fault current from the equipment flows through the earthing system to the earth and thereby protect the equipment from the fault current. At the time of the fault, the earth mat conductors rise to the voltage which is equal to the resistance of the earth mat multiplied by a ground fault.
The contacting assembly is called earthing. The metallic conductors connecting the parts of the installation with the earthing are called electrical connection. The earthing and the earthing connection together called the earthing system.