# Substation Earthing System ( Grounding System ) – Earthing Mat

- Link: https://studyelectrical.com/2014/05/substation-earthing-system-grounding.html
- Published: 2014-05-21T04:02:00+00:00
- Author: 

The substation earthing system comprises of a grid (**_earth mat_**) formed by a
horizontal buried conductors. 

> [Read about design of substation earthing system here.](http://www.studyelectrical.com/2017/01/substation-earthing-system-design.html)

The grounding system in [substation](https://studyelectrical.com/2019/04/electrical-substation-equipment-types-components-functions.html)
is very important. The functions of grounding systems or earth mat in include:

 * Ensure safety to personnel in substations against electrical shocks.
 * Provide the ground connection for connecting the neutrals of stat connected transformer
   winding to earth ( neutral earthing ).
 * Discharge the overvoltages from overhead ground wires or the lightning masts 
   to earth. To provide ground path for surge arresters.
 * Provide a path for discharging the charge between phase and ground by means of
   earthing switches.
 * To provide earth connections to structures and other non-current carrying metallic
   objects in the sub-station (equipment earthing).

In addition to such a grid below ground level, earthing spikes (electrodes) are 
driven into the ground. They are connected electrically to the earth grid, equipment
bodies, structures, neutrals, etc. All these are connected to the station earthing
system by earthing strips. 

 

If the switchyards have a soil of low resistivity, earth resistance of the earthing
system would be low. If the soil resistivity is high, the mesh rods are laid at 
closer spacing. More electrodes are inserted in the ground.

  |  ⌊WP 20140315 10 43 58 Pro⌉ |  
 |  Earth Mat in 110kV side of a  220/110 kV Substation  |

The fence, equipment body, tanks, support, structures, towers, structural steelworks,
water pipes, etc. should be earthed. 

### Earth Resistance Value

The value of earth resistance of the ground system determines the voltage rise of
the various earthed points during the earth fault. 
  If earth fault current is 
I, earth resistance is R, the voltage rise under short circuit condition would be
V= IR.   The permissible potential rise and the maximum possible earth fault current
set a limit on the maximum value of earth resistance.   To achieve earth resistance
within specified limits, enough number of earth spikes and sufficient surface area
of the earth grid and closer ground mesh rods are necessary.  The touch potential
and earth potential in the switchyard under any earth fault condition should be 
within safe limits.

> [Substation Earthing System Design](http://www.studyelectrical.com/2017/01/substation-earthing-system-design.html)

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