I am reviewing a ground grid study for a substation that is being built. The ground grid will be for a substation with a high side of345kV and two transformers that step the low side voltage down to 34.5kV. My question is why was the ground fault current (6.399kA) of the high side used on the ground grid study and not the low side current (26.825kA)? Is this correct? I would think the load side short circuit current would be used since it is larger.