EARTHING OR GROUNDING


In electrical supply systems, an earthing system is circulatory which connects parts of system with earth to protect the system.


PURPOSE OF EARTHING:- 


  • To avoid electric shock to human body.
  • To avoid earth leakage accidents through damp situations.
  • To avoid risk of fire due to earth leakage current through unwanted path.
  • To discharge high voltages to the earth i.e. also some what protection from lighting.   

EARTHING METHODS:-


Following methods are mainly used for earthing power equipment's through neutrals namely.

  • Earthing through a resistance :- In this method parts of system are connected through resistor to the earth.
  • Earthing through a reactance:- In this method parts of system are connected through reactance to the earth.
  • Earthing through a Peterson coil:- In this system parts of system are connected through Peterson coil to the earth.

  • Direct Earthing or Solid Earthing:-In this system parts of system are connected directly to the earth through solid wire.

PERMISSIBLE VALUES OF THE EARTH RESISTANCE :-

  • Large power station :- 0.5 ohm.
  • Major power station:- 1.0 ohm.
  • Small substations:- 2.0 ohm.

Total Earth Resistance Depend On:- 

  • Resistance of the metal electrodes.
  • Contact resistance between metal electrode and the earth.
  • Resistance between electrode surface and the infinite earth path.
  • Temperature also effect the resistivity of the earth. 

DIMENSION OF THE EARTHING PLATE:-

  • Copper plate : 60 X 60 cm² X 3.15mm.
  • G.I. Plate : 60 X 60 cm² X 6.3mm.
  • C.I. Plate 60 X 60 cm²2 X 1.2mm.

PIPE/ROD:-

  • G.I Pipe:- 2.5 to 3 m length , 100 mm dia