MV Supply Side Bonding Jumper

[philly]

Looking at a project in a substation for renewable site where the 34.5kV delta side of GSU feeds a 34.5kV switchgear lineup. The switchgear lineup which serves the site collector feeders also feeds a zig-zag grounding transformer which derives the grounding reference for the 34.5kV system.

My question is in this application what are the equipment ground conductors between GSU secondary and switchgear considered? Usually with a wye grounded transformer for a SDS these are considered supply side bonding jumper and sized in accordance with 250.102. Would these still be considered supply side bonding jumper, or would these be considered equipment grounding conductor or something else?

 

[JoeStillman]

I would call it a grounded circuit conductor. I assume it's grounded at both ends. It provides the path back to the neutral point for ground fault current.

 

[don_resqcapt19]

It is not used as a circuit conductor, so I see it as a supply side bonding jumper..

 

[JoeStillman]

It is not used as a circuit conductor, so I see it as a supply side bonding jumper.

It's a fair point to assume there is no line-neutral load. So if there is line-to-neutral load it's a grounded circuit conductor, but if all loads are 3Ø, 3W, the same wire would be a supply side bonding jumper?

 

[jaggedben]

It's a fair point to assume there is no line-neutral load. So if there is line-to-neutral load it's a grounded circuit conductor, but if all loads are 3Ø, 3W, the same wire would be a supply side bonding jumper?

He said the supply was delta and the zig-zag that provides a grounding reference is connected to the switch gear. And he is asking about bonding between supply and switchgear. With those givens, I don't see any wire that could be a grounded circuit conductor.

 

[JoeStillman]

He said the supply was delta and the zig-zag that provides a grounding reference is connected to the switch gear. And he is asking about bonding between supply and switchgear. With those givens, I don't see any wire that could be a grounded circuit conductor.

I see your point. I'm just surprised to see a utility service that has no return path for ground fault current.

 

[jaggedben]

I think he saying it is a customer owned separately derived system.

 

[electrofelon]

I see your point. I'm just surprised to see a utility service that has no return path for ground fault current.

How do you propose that would be accomplished on a delta distribution system?

 

[JoeStillman]

How do you propose that would be accomplished on a delta distribution system?

Do they even do that?

 

[electrofelon]

Do they even do that?

Most/much/a lot of the distribution here in upstate NY is 4800 delta. @mtnelect should move here!

 

[electrofelon]

But I hear you it is odd to consider that a pad mount transformer that is sitting right out in the open accessible to people has no fault clearing path. Not sure if a 4800 fault to dirt will clear or not.

 

[jaggedben]

But I hear you it is odd to consider that a pad mount transformer that is sitting right out in the open accessible to people has no fault clearing path. Not sure if a 4800 fault to dirt will clear or not.

In the past people have posted designs where there is some kind of relay tied into the zig-zag, iirc.

 

[electrofelon]

In the past people have posted designs where there is some kind of relay tied into the zig-zag, iirc.

I was thinking more of utility owned transformers. Im not really sure how faults are handled on these ungrounded distribution systems.

 

[philly]

The application here is a HV substation 69kV -34.5kV so not a standard utility service entrance. Service entrance is on 69kV primary so transformer and 34.5kV secondary is customer owned.

Switchgear bus on the 34.5kV secondary (delta winding) has a zig-zag grounding transformer that sources ground fault current with relay detection for tripping breakers upon detection of ground fault.