How to ground a 10kV switchgear?
I have a high rise project where the building incoming servicce is at 10kV and the building owner owns and is responsible for the maintenance of all medium voltage and low voltage systems.
With that said, there are multiple substations at each mechanical level in the tower. Instead of running separate cables to each substation, I have decided to have a 10kV switchgear on each mechanical floor to feed the multiple substations on that floor.
I intent to run a 500kcmil grounding electrode conductor up the building for the purpose of grounding the transformer secondary. Let's assume I sized the GEC properly.
The GEC will run from the MEGB main electrical room ground bar to a ground bar in the substation room on the mechanical floor and then to the transformer secondary neutral/ground.
How do I ground the 10kV gear? First, medium voltage distribution is 3 wire plus ground, right? All delta. Which is why the gear only has a ground bus and no neutral bus, right?
I can rationalize the 10kV gear grounding 2 ways:
1 - Follow low voltage distribution logic meaning that the medium voltage switchgear is grounded through the ground wire within its 10kV feeder cable.
Following LV distribution logic, an (EGC) equipment grounding conductor would ground tha LV panel, so similarly the ground within the 10kV cable should ground the 10kV gear, right?
2 - Run a ground wire from the mechanical floor ground bar mentioned above to the 10kV gear ground bus. Is this now multipoint grounding similar to how the utilities ground their MV lines? Multi-point because the gear is grounding through the riser GEC and the feeder EGC?
3 - Thought of a third scenario. What if the 10kV cable does not have a ground wire? Then I assume the 10KV gear would have to be grounded through the GEC riser. But technically the 10KV gear isn't a separately derived source (SDS) and doesn't technically require a GEC, just a ground. Should I provide a separate ground conductor for the 10kV systems? Or can I use the same ground conductor for both LV and MV systems?
Any thoughts are really appreciated.
Thanks in advance.
I have a high rise project where the building incoming servicce is at 10kV and the building owner owns and is responsible for the maintenance of all medium voltage and low voltage systems.
With that said, there are multiple substations at each mechanical level in the tower. Instead of running separate cables to each substation, I have decided to have a 10kV switchgear on each mechanical floor to feed the multiple substations on that floor.
I intent to run a 500kcmil grounding electrode conductor up the building for the purpose of grounding the transformer secondary. Let's assume I sized the GEC properly.
The GEC will run from the MEGB main electrical room ground bar to a ground bar in the substation room on the mechanical floor and then to the transformer secondary neutral/ground.
How do I ground the 10kV gear? First, medium voltage distribution is 3 wire plus ground, right? All delta. Which is why the gear only has a ground bus and no neutral bus, right?
I can rationalize the 10kV gear grounding 2 ways:
1 - Follow low voltage distribution logic meaning that the medium voltage switchgear is grounded through the ground wire within its 10kV feeder cable.
Following LV distribution logic, an (EGC) equipment grounding conductor would ground tha LV panel, so similarly the ground within the 10kV cable should ground the 10kV gear, right?
2 - Run a ground wire from the mechanical floor ground bar mentioned above to the 10kV gear ground bus. Is this now multipoint grounding similar to how the utilities ground their MV lines? Multi-point because the gear is grounding through the riser GEC and the feeder EGC?
3 - Thought of a third scenario. What if the 10kV cable does not have a ground wire? Then I assume the 10KV gear would have to be grounded through the GEC riser. But technically the 10KV gear isn't a separately derived source (SDS) and doesn't technically require a GEC, just a ground. Should I provide a separate ground conductor for the 10kV systems? Or can I use the same ground conductor for both LV and MV systems?
Any thoughts are really appreciated.
Thanks in advance.
