Neutral Grounding

Hi all, dont know if this forum is the correct one, but I know many here could answer this question..

There is a project, where a subcontractor will be doing the substation local, and all its related electrical stuff from the MV side..

I have been discusing with him the low voltage side, specially the grounding of the neutral.

The transformer will be a dry 1000KVA, 15/0,4KV delta/wye.

The transformer will be 80meters away from the facility.

First question.

Should we carry the PE cable from the substation till the facility ? im asking this from a practical point of view. I know this has to be done if the distribution system we use is TN-S and the neutral is grounded in the substation. but should we ? is it worth ?

Could we only carry the neutral and ground it just before the facility ?

We could also use TT system and then we would have 2 independent grounds, one in the substation for the neutral and another one in the facility.. in this case i MUST use residual circuit breakers,

The reason why i would like to use TN-S system is because the phase-ground faults would have a much higher current and if designed correctly the magnetic of the circuit breakers would trip in each branch circuit.

This will be a facility with a lot of motors.

Anyway if using one or the other distribution system I will put a toroid with a ground fault relay, regulated high enough so it doesnt trip incorrectly.. in the main circuit breaker of the facility.

Open to opinions, thanks!

scheme

with TT

All of the setups I have seen would follow "B" in your drawings.

Ground at the main panel of the facility. Only one place as with a dual ground there is a chance (isolated but real) that there could be current flowing through the PE wire or the Earth itself.

Similarly in houses the main panel has the neutral grounded in it, not the transformer or the meter box. And not any sub-panels.

that answer is best left to the engineer that designed the system. it is their responsibility to have ground resistance testing and they have the credentials.
going around their design can land you, and your company in big trouble if something went wrong or someone got injured.
james

James Mcquade said:

that answer is best left to the engineer that designed the system. it is their responsibility to have ground resistance testing and they have the credentials.
going around their design can land you, and your company in big trouble if something went wrong or someone got injured.
james

Click to expand...

James I know that. And thats why I want opinions based on your experience, and what you have seen done. I know the possible óptions, and measures to be taken, but I want to know others opinions. A subcontract will do this work. And when they come up with the solution I want to be able to discuss their choice.

Thanks!

I believe the ground of neutral should be done at the transformer.
However...electrical utility companies are not required to install equipment grounding conductor.

A nice read...
https://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/Neutral-to-GroundConnections~20020521.htm

NetNathan said:

I believe the ground of neutral should be done at the transformer.
However...electrical utility companies are not required to install equipment grounding conductor.

A nice read...
https://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/Neutral-to-GroundConnections~20020521.htm

Click to expand...

Hi Nathan, in this case the utility company will supply in 15KV 3phase. We will have our own substation 15/0,4KV. Si its our choice the ground system to use. I mean TT or TN-S could be valid. If the substation was next to the building defenetly the option is TN-S, but as the substation is far away i believe TT Makes sense also, so I dont have to carry the PE conductor from the substation.

Simply put, it’s not a “neutral” if it’s not grounded and a neutral is only grounded in one location (per USA NEC rules).

It’s been my experience that if the neutral is not grounded at the transformer then it’s grounded at the neutral bar in the main panel.