Design Of Earthing Mesh

The parmeters for designing a grounding mesh are in order of priorty: power handling capapbility of the sud-station wrt the fault currents generated for single and three phase faults .

the faults current levels will determine the conductor sizes.

substatons close to power plants will have higher fault current levels than distrubutuin substation with many mile of transmission line with associated impedances.

te soil conductivity and protection fronm touch and step voltages.

Hi,

I have never used a mesh (only spikes) so my reply may
not be accurate; however I was taught the earth:

Connection to be at least equal to, and preferably greater than,
the capacity of the circuit it protects. (to carry the current.)

Be at least 4 feet, and preferably 6 feet, down below ground
level. (to avoid the ground drying out, making the earth HR.)
Some water absorbent material can be used around the earth.

Be resistance measured to be certain it is not high res. (HR)

Pretty obvious, but hope this helps.

jt.

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The design procedure is and calculations are long.Parameters are as rightly pointed in a reply the fault current at substation bus,and fault current values. If this is not available normally use Incoming breaker's fault current value. The other important thing is limiting the touch ,step potential to sfae limits.

Long ago I worked on this assignment. Firstly at various locations of the substation site, the earth resistivity was measured. Then step voltage was decided. Short circuit level was worked out. Assuming the earth resistance to be 2 ohms, the length and size of earthing conductor was calculated. Thereafter, the size of the mesh was determined. But i have forgot the methodology: I would request guidance in the matter.

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