Transference of earth fault currents to PV Plant Earthing System from interconnect substation

[E. Kermendy]

We are involved in a 90 MW PV in construction project. The interconnect station (33/132 kV) is exactly as those shown in IEEE 2778, neighboring the PV farm.

The GPR is quite high (about 8 kV) at substation due to several reasons, as 22 kA short circuit power, quite small switch yard (40x45 m), poor soil resistance.

Some colleagues feel that interconnecting both grounding grids as stated everywhere can “send to PV farm” dangerous fault currents from substation.

The software that we are using is CYMGRID and ETAP were we are not able to simulate and monitor specific currents (is it possible? we do not know how to make the software calculate what we need), I mean, simulate 22 kA fault in substation and monitor currents and GPR in PV farm. Currently, we are simulating separately both grids, end even worse we do not trust simulation of a 1 square km PV farmland, with a 200 A short circuit power supplied by grounding zigzag transformer in the 33 kV delta system, since both applications are meant for substation analysis.

Any idea, similar experience or suggestion will be appreciated.

 

[DBL-E]

I saw you other, similar post, and just wanted to get back on this one as well.

Typically grounding systems mutually benefit by interconnecting, as you reduce the grid resistance and lower the GPR. As your colleagues point out, making that connection does transfer the potential out to the PV system, but you might already have a problem where they are close. Also are you running cables with neutrals that are providing that metallic connection anyway?

The software that doesn't consider the self impedance or mutual impedance are going to give inaccurate results for large systems like PV, so you need a software like CDEGS/XGSLab that can do that or work with a firm that has those tools.