Hello, I am new to substation gr

[Yeti8848]

Hello,

I am new to substation ground grid design. I am workign on a project to design a ground grid that houses two substation transformers, each feeding a separate PV farm. With sufficient distance between between two oil filled XFMRs, I am thinking of having a single ground grid. My main concern is how do we consider the incident fault levels (to determine the potential profiles)? Like, do we double the fault levels (assuming a simultaneous occurrence of fault at the both sites). I dont think that is needed here, since both of the XFMRS are close and will interconnect with utility in same area. Any thoughts? Thanks in advance!

 

[cuky2000]

Considering the short circuit contribution of the PV is close to the FLC of the system, the worst case scenario for short circuit is from the utility side. If one of the transformer winding is connected in delta, possible the design short circuit will be based on the HV side. Therefore the impact for designing the ground grid will be more favorable.
Not sure how far are the two substations mentioned in your post. Perhaps may be logical to consider just couple interconnecting grounding conductors between he two substations.

 

[jghrist]

The return current for a fault on the secondary of the transformers will flow through the single ground grid to the transformer source. None of the current will flow through the earth, so the fault current will not affect GPR, step-, and touch-voltages. The fault current to consider is the high side fault from the utility source. As cuky noted, there will be insignificant fault current from the PV plant.

 

[7anoter4]

If a short circuit occurs between a phase and ground on the grounding grid the transformer current does not participate in potential rise since grounding grid resistance conveyed the most of current and the parallel current through the Earth is negligible. But if the short-circuit occurs in the network then part of the transformer current passes through ground and part returns from the fault location through network grounding [static wire] to the transformer directly.

 

[7anoter4]

This is the second case: