Overhead 13.8kV Feed

[dougjl]

Hi,
I have a customer who has asked that a 13.8kV feed be fed overhead about a mile to a 13.8kv/4.16kV transformer. NESC says that a ground connection should be made to the neutral at the source. The issue is the switchgear that will be feeding this line is only 3W 3PH. Where do I get my ground? It would seem that I would want one to run with the phases. Do you think just connecting to the ground grid at the source and then grounding every couple of poles would be the correct way to look at this? And if so would I run the ground below the phases as a neutral would be typically run or would this become in essence a shield wire and need to be located above the phases?
Thanks,
Doug

 

[RRaghunath]

13.8kV is generally 3-wire distribution. Neutral is grounded at the grid transformer itself and is not brought to the switchgear.
The NESC is speaking of the neutral grounding at the grid transformer upstream.
Running a shield wire and earthing it at every alternate pole is recommended and is also governed by the local codes / practice.

Rompicherla Raghunath

 

[dougjl]

Thanks for that information. I am a bit confused about a shield wire. I have seen installations of higher voltages where the shield wire is located above the current carrying conductors, which makes sense in my mind for lighting protection etc.
But, as I look around at the poles in the area there is a ground/neutral running below the current carrying conductors. There are usually three current carrying wires, one on each side of the cross arm and one on top of the pole and then a ground/neutral running below that. Is the ground/neutral considered a shield?
Thanks,
Doug

 

[waross]

I have seen the neutral/ground wire that is normally in a lower position transposed to the top position were the line is at higher elevations and more subject to lightning.
The system was on an island and where the line crossed over a hill it would be the highest point for quite a distance. his is where the neutral/ground was transposed and also served as a guard wire.
This was a 13.2 kV system with wye:wye transformer banks for both supply and utilization.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[aussiejohn2]

Hi Dougjl,
I would call that an underslung ground/neutral, and would not consider it to provide any lightning shielding at all. It helps significantly with improving protection operating times for (many) faults, with reducing EPR issues where earthing is difficult, and with reducing induced voltage into telecommunications circuits and other adjacent conductors.
John.

 

[RRaghunath]

It is unusual to have neutral wire in MV/HV distribution. It is generally 3-phase, 3-wire distribution.
It is Shield wire if provided on top.
Some times, additional ground wire or grounded mesh is strung below the phase conductors just to make sure in case if one of the phase conductors happens to fall down, it will touch the ground wire and thus definitely ensure the earth fault protection operates.
This is very relevant in rocky and other terrains that offer high earth resistance.

Rompicherla Raghunath

 

[dougjl]

Thanks to all for the responses.

 

[stevenal]

It is unusual to have neutral wire in MV/HV distribution. It is generally 3-phase, 3-wire distribution.

Very common in North America. The neutral is a current carrying conductor intended to carry unbalanced current.