Sustaion Earthing resistance

For 66/11KV sub station, yes, earth resistance shall be maintained (practically) within 2 ohm. If you are able to achiev within ONE ohm is very good. You can achiev this by following methods

• Use CI pipe earthing or
• Connect more no of GI / Copper earth pits( Plate or pipe earthing) in series or
• Crerate more earth mats with 50x10 sqmm Copper flat
• By chemical earthing if your natural earth resistance is more
• Use bentonite clay to increase the erth resistance by increasing water retntion
• Mainly check tightness and increase the area of contact

Most substations, I have built, had to be < 1 ohm. As the other fellow said, series of grd rods or a deep well, we used a deep well with a series of grd rods. Its not so much as the star connection, but the fault current and the lightning protection.

The old criterion used to be <1ohm to combine HV/LV earths....but the KEY issue is the magnitude of the 'fault current' that the earth system will need to handle safely.

Newer regulations are steering away from the 1 ohm rule and more towards using modelling software such as CDEGS to 'prove' the safety of your design/install by modelling the EPR (earth potn rise).

Go to http://www.sestech.com/ for details of the s.ware and/or www.ees-group.co.uk for more info.