Earthing Network

Hi,
I have to design the earthing network of a 25 MW base load gas turbine driven power plant. Can u please give me the guidelines for the design, what are the criteria and how to select the conductor size for individual equipment and the main earthing bar, what points should be kept in mind. Besides plz give me useful references on net.
thanks and regards.

 

[busbar]

For IEEE territory, standards 80, 142 and 837 are a good place to start.