CYMgrd or ETAP simulation of PV and SS earthing grid interconnected.

[E. Kermendy]

Is CYMgrd or ETAP able to model the interconnection of a solar PV farm earthing grid interconnected with its interconnect substation earthing grid?

The issue is that when injecting the short-circuit currents from the substation into the earthing grid of the PV plant, it does not support it, because there will be no faults of the magnitude of the faults in the substation in the PV zone.

That is: Is it possible to simulate faults differentiated by zone? and evaluate the effect of short circuit in the substation (high fault values) on the PV zone (very large area with weak phase-to-ground short-circuit currents).

 

[waross]

A ground fault at the substation will cause a ground potential rise near the ground grid at the sub and near the location of the fault.
With no discontinuities in the soil conduction the value of the ground potential rise drops off rapidly with distance.
The reduction is between an inverse square and an inverse cubic function.
If you interconnect the ground grids you may transfer some GPR from the sub to the area of the PV grid.
Left unconnected, little of the sub GPR will reach the PV grid, and the PV grid will tend to keep the exposed surfaces at the GPR value.
he action of a PV grid that is not connected to the sub grid will be similar to an equipotential switching mat.
Interconnecting the sub ground grid and the PV ground grid may introduce hazards of tpouch potentials and step potentials where none need exist.

Will your software plot the Ground Potential Rise as a function of the distance from the ground grid?



--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[E. Kermendy]

Thanks for answering.

I copied the response, to write on it, our way to see the Electromagnetic world, with Ohm's law lenses.

A ground fault at the substation will cause a ground potential rise near the ground grid at the sub and near the location of the fault. = AGREE

With no discontinuities in the soil conduction the value of the ground potential rise drops off rapidly with distance. YES

The reduction is between an inverse square and an inverse cubic function. = YES, AS A FUNCTION OF THE RADIAL DISTANCE FROM FAULT SITE.

If you interconnect the ground grids you may transfer some GPR from the sub to the area of the PV grid. = YES, THE PV FARM WILL FOLLOW THE SS POTENTIAL, MAKING SMALLER VOLTAGE DIFERENCE BETWEEN SS AND PV PLANT.

Left unconnected, little of the sub GPR will reach the PV grid, and the PV grid will tend to keep the exposed surfaces at the GPR value. = PERSONALY I CAN NOT SEE IT THIS WAY, BECAUSE AS SEEN BEFORE, GPR DECREASES AS DISTANCE INCREASES

The action of a PV grid that is not connected to the sub grid will be similar to an equipotential switching mat. YES, UNCONNECTED PV SURFACE AQUIPPED WITH EARTHING GRID WILL BE EQUIPOTENTIAL, AT ITS OWN POTENTIAL.

Interconnecting the sub ground grid and the PV ground grid may introduce hazards of touch potentials and step potentials where none need exist. = I CAN NOT SEE IT THIS WAY. WHAT WE SEE IS THAT INTERCONECTING (AS EVERYWHERE IS WRITTEN) WILL EQUILIZE POTENTIAL OF PV WITH POTENTIAL OF SS. AOUTSIDE OF BOTH EARTHING GRIDS, POTENTIAL WILL DECREASE.

Will your software plot the Ground Potential Rise as a function of the distance from the ground grid? YES. BUT WITH SHORT CIRCUIT CURRENTS ANALYZED IN PV PLANT, WHERE THIS HIGH CURRENTS CAN NOT OCCUR. I WANT TO TELL CYMGRD/ETAP TO NOT SIMULATE HIGH CURRENTS IN PV ZONE/AREA AND WE HAVE NOT FOUND THE WAY TO INSTRUCT BOTH PROGRAMS NOT TO ANALYZE HIGH CURRENT EVERYWHERE IN THE GRID, ONLY IN THE SS AREA.

THANKS TO ALL THAT TOOK THE TIME TO READ THIS NOVEL

 

[DBL-E]

The problem you are seeing is a limitation of simpler analysis programs that have an 'equipotential plane' assumption. Essentially ignoring the voltage drop that occurs in the metal earthing/grounding system. With a well meshed earthing system, these tool can be reasonably accurate up to a certain size (<150m) and that depends on the soil resistivity, as you can see greater voltage drop with larger systems and lower resistivity. In systems that are larger, this assumption affects the calculated resistance, affecting your GPR/EPR, and thus your touch voltages.

Software like XGSLab (GSA_FD or XGSA_FD) or CDEGS (MALZ or HIFREQ) will have you specify a fault location and a reference for your touch voltages, so when you don't see that type of data entry the software is probably using a simplified calculation method. Also the soil modeling tends to be pretty limited with the simpler software programs, which might be an issue as you can see more changes in strata as you large PV grid is affected by great volume of soil.

Regarding the fault current in the PV, do you have an NGR to limit the magnitude of fault current? Also do you need to look at voltage to a perimeter fence?

 

[jghrist]

Even if the grids are not deliberately interconnected, there will be a rise in potential on the PV grid for a high side fault on the SS grid. This is because the cable shields and/or neutrals connect to both grids. Some fault current returns to the SS source through the cable shield/neutral and into the soil at the PV grid. This transferred potential cannot be calculated easily.