Earthing is an integral part of all electric installations whether it is generating station, a transmission/distribution system or an industrial/commercial or domestic user. A properly designed grounding system ensures correct operation of protective devices on occurrence of earth faults or lightning strikes, safety of equipment and personnel and prevents build –up of electrostatic charges or occurrence of dangerous induced voltages on equipments and structures.
An earthing system is the total set of measures used to connect an electrically conductive part of the power system to earth.The earthing system is an essential part of both high and low voltage electric power networks and has at least four important electrical rules:
1. For correct operation of the electric network, leading to good power quality.
2. To ensure electrical safety for exposed humans and animal by
a. Fast identification of faults, leading to reduced fault duration
b. Limiting touch and step voltages and resulting body currents to safe values.
3. To protect against lightning by:
a.Limiting potential differences across electrical insulation on stricken equipment
b.Provide low-impedance paths for dissipation of stroke current energy
4. To contribute to electromagnetic compatibility
Earth electrodes are bare conductors buried in earth.They may be simple electrodes viz.vertically buried bare rod/pipe/plate electrodes, horizontally buried bare strip/round electrodes that may be called a grid earth electrode. When a fault to earth occurs in which a live conductor is in contact with an earthed conductor, the earth electrode facilitates flow of earth fault current to earth: this current is collected at one or more other electrodes which may be at varying distances from the electrode where the current enters the earth .For all practical purposes the collecting electrode is assumed to be a metal hemisphere.
The current dissipates from the earth electrode into soil from its surface and leaves the surface perpendicular to it. However at a large distance from the electrode, compared to its dimensions, the current flow can be assumed as if it is radiating from appoint at the center of the electrode. For more details please log on to http://www.alfredkim.com.