120/240 closed delta backfeed

[tortuga]

In the case I'm applying this, the transmission company is receiving power from the local transmission utility. The connection is primary metered and the transformer is owned by the transmission company. Which puts the transmission company behind the utility meter, and hence under the NEC code.

Nothing in the NEC draws a line on a utility meter, its a myth. See 'service point' definition in article 100.
Also it sounds like the 'transmission company' is engaged in the business of transmitting power they might also be a 'utility' and thus exempt from the NEC see 90.2(B)(5).
But that being said if you want to apply the NEC to your utility (as in your place of employment and your the specifying engineer) your free to do so. I have herd of telcom utilities that choose to apply the NEC where they are not 'required' to by the local jurisdiction, rather by their own choice in 'System Practices' manuals.

 

[tortuga]

Thats kinda interesting, so there is no electrical connection between these two utilities. Its as if BPA had a 230kv transmission line and had a substation for it, but instead of powering the substation off the 230kv line they bring in power from a local POCO and primary meter it.
So a utility is a customer of a utility.
I still dont think the NEC would apply but that is a odd case.

 

[Hv&Lv]

I might be a bit foggy care to give a refresher?
We're talking about the diagram in post#13 right?
I do remember a plant that had seeming lost a primary phase and the 3 phase motors were still running.
It was old 240 D.

Here is an open delta, notice the high side is grounded. On that post in 13 it’s an open wye. High sides not grounded.

 

[jim dungar]

Here is an open delta, notice the high side is grounded. On that post in 13 it’s an open wye. High sides not grounded.

Also a blown fuse feeding a transformer bank does not create a true open delta unless it was arranged such that the physical delta connection was also broken.

 

[kwired]

Thats kinda interesting, so there is no electrical connection between these two utilities. Its as if BPA had a 230kv transmission line and had a substation for it, but instead of powering the substation off the 230kv line they bring in power from a local POCO and primary meter it.
So a utility is a customer of a utility.
I still dont think the NEC would apply but that is a odd case.

Around here all rural and smaller city municipal power companies typically purchase energy at wholesale rates from another larger POCO that has generating plants, transmission systems, as well as supplying individual customers in other surrounding communities.

 

[jaggedben]

Around here all rural and smaller city municipal power companies typically purchase energy at wholesale rates from another larger POCO that has generating plants, transmission systems, as well as supplying individual customers in other surrounding communities.

Yeah, but the municipal power company is still a utility and wouldn't ordinarily be required to follow the NEC at a substation where such a transfer occurs.

 

[tortuga]

Here is an open delta, notice the high side is grounded. On that post in 13 it’s an open wye. High sides not grounded.

I see, but in the scenario we are talking about the A phase is a downed line after a storm or other failure, grounded in many places, possibly laying across the neutral.
But your right the first transformer is in series with the grounded A phase.

 

[kwired]

Yeah, but the municipal power company is still a utility and wouldn't ordinarily be required to follow the NEC at a substation where such a transfer occurs.

The wind farms that have popped up in recent years around here at not utility owned or operated. All their facilities were subject to inspection and NEC compliance. Not sure exactly where the utility starts and the wind farm ends in the substation where they connect to the grid though. I did get a call when they were constructing one of them - they needed qualified license holder. Probably would have been easy money but I turned them down.

 

[Hv&Lv]

The wind farms that have popped up in recent years around here at not utility owned or operated. All their facilities were subject to inspection and NEC compliance. Not sure exactly where the utility starts and the wind farm ends in the substation where they connect to the grid though. I did get a call when they were constructing one of them - they needed qualified license holder. Probably would have been easy money but I turned them down.

It would have been easy money, but if it’s like some around here, they won’t accept your suggestions, want it done their way whether some of it is legal or not based on a designers print.

 

[tortuga]

Around here all rural and smaller city municipal power companies typically purchase energy at wholesale rates from another larger POCO that has generating plants, transmission systems, as well as supplying individual customers in other surrounding communities.

Right you see that all the time. Town utility 'A' purchases power from big transmission utility 'B', power is handed off at a substation.
Occasionally you see a small utility 'C' like a wind farm that sells power to 'B', and voluntarily adpots the NEC (probably for OSHA and insurance) though they would be exempt local/state jurisdiction wise per 90.2.

But if I am understanding the OP correct this is a generation/ transmission utility we'll call them BPA and say they operate a large line of towers with a 230kv line.
Now BPA needs to put in what the OP is calling a 'substation', but technically for whatever reason this substation is not handing off power to utility 'A'.
At this station there might be a switch or buck boost transformer who knows, but its not handing off power.
Now presumably for cost reasons BPA had utility A bring in a 'primary service' at 12.5kv to power a 240 delta bank for

large transformer pumps and fans.

There is no utility to utility power sales at this substation, its 230kv in 230kv out, for utility A its just like any other primary customer, there is a meter on the 12.4 kv line and they go read the meter and send them a bill. A's responsibility ends at the primary meter.

Utility A (the OP) apparently does not offer 'delta' services becasue of this alleged problem, but they can't control what their primary customers do transformer wise, so the OP is looking for a (non existent) NEC section that essentially prohibits a main breaker for staying on if a phase is lost, rather than installing protective relays that would detect such a situation.
In a way any delta connected 3phase motor would do the same thing.

 

[kwired]

It would have been easy money, but if it’s like some around here, they won’t accept your suggestions, want it done their way whether some of it is legal or not based on a designers print.

One my reasons was concerns over falling behind on other work I was already doing. Technically all I had to do was be on site for supervision for licensing reasons. If any of them had state journeyman licenses then I guess I wouldn't even needed to be on site much if at all. Otherwise all they needed was to be registered as apprentices to legally do the work as long as a license holder is also on the job.