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SYSTEM EARTHING The general purpose

SYSTEM EARTHING

The general purpose of earthing is to protect life and property in the event of 50/60 Hz faults (short circuit) and transient phenomena (lightning switching operations). The question of how a e/stern shall be earthed is designed by regulation. The regulation that one point of every system shall be earthed is designed primarily to preserve the security of the system by ensuring that the potential on each conductor is restricted to such a value as is consistent with the level of insulation applied.

The choice of the earthing method is based on the following criteria :

• Voltage level : the insulation level of material must be in accordance with the induced voltage at the time of fault.
• Insulation co-ordination.
• Limitation of fault current : to reduce the electrodynamics stresses on material, to limit the induced voltage on telecommunications lines and over voltage on LV components.

There are 3 methods of neutral earthing:

Insulated neutral system (fig.1)

Direct earthing or solidely earthedx (fig.2)

Impedance earthing (fig.3) - The purpose of this method is to limit the current for greater safety.
There are 3 type of impedance earthing:

1. Earthing through reactance.
2. Earthing through ARC - Suppression coil.
3. Earthing through resistor.

Source : MDResistor.com