Switchyards and Earthing Conductor Sizes

It would be inadvisable for the earthing conductor to be of a smaller cross-section than the largest of the phase conductors, for a start.

Dear Rajesh,

Looks like you are dealing with HV Substation earthing system, that's why it isn't the same as the earthing conductor sizing at LV system.

In your case, the conductor sizing is depend on,

1. Rated System Voltage

2. Short Circuit Current Level ( e.g 16 kA, 25 kA, 31.5 kA or 40 kA ), usually for 400 kV system we choose 40 kA.

3. Step and touch voltage.

You can get the detail theory and calculation sample at :

1. IEEE 80-2000." IEEE Guide for safety AC Substation Grounding.

2. Power Substation Engineering. by John Douglas McDonald

chapter 11.3.6.2

Regards,

Stanyadji

hi thankyou very much for giving reply but i dnt have IEEE std 80 edition to calculateplease can u help regarding this?

http://webstore.ansi.org/RecordDetail.aspx?sku=80-2000&source=google&adgroup=ieee&keyword=ieee%2080&gclid=CJHq-NTs5poCFQJ2xgodS0IFjw

Download it here. You could have done a google search and found it yourself.