Grounding Design

[Amex12]

I am doing the grounding design for a small padmount transformer adjacent to a building. The transformer is a delta-wye (27.6 kV-600 V) and it is connected to a 44 kV pole from the Utility with no shield wire. I am not to consider any split factors in my design.

My question is, what do I consider as the actual earth current during a ground fault? I have been given the L-G fault values from the Utility at the connection point. Do I use this value for step and touch/GPR calculations or do I consider the current on the secondary side from a primary side fault?

 

[7anoter4]

It is not so clear what is about. First the transformer has to be 47/0.6 kV and the last pole has to be on your premise wiring yard located. If you are spoking about GPR that means you have a grounding grid in the yard soil. If the low voltage does not extend over the fence-that means the supplied installation are entirely on this grid- no potential rise will be due to low voltage since the short-circuit current flows only through the grid and not through the ground. Only 44 kV Line supplies the short-circuit current which will rise GPR.

 

[Kiribanda]

In Canada, per CSA you should put a minimum of four 10ft ground rods around the pad mounted transformer
and interconnect them like a loop using a conductor adequately sized for the available maximum
ground fault current at the location. You should bond
1) All metallic parts of the transformer to this loop
2) You should bond the secondary neutral to this loop
Since you are bonding the Sec Neutral to the loop as mentioned in (2) above, the max ground fault current
should be the prospective ground fault current at 44kV high side.