Wye to wye questions

[hhsting]

Attached sketch shows from left to right: 600VAC inverters feeding customer owned 600V, 3000A service rated switchboard which has neutral to ground bond, GEC to ground grid and feeds 2000kVA 600VAC to 13.2kVAC customer owned transformer wye to wye. The transformer has no neutral to ground bond but has GEC to ground grid and bonding jumper from 600VAC switchboard goes to transformer gnd bar. The transformer then feeds via (3)#1 AWG 15kv MV-90 with concentric neutral to 15kV customer owned switchgear 125A fuses disconnect. The point of interconnection is shown in sketch after the 125A fuses in15kV switchboard. Their is bonding jumper from transformer to 15kV switchboard #1 AWG GND and their is again GEC from 15kV swbd to ground grid.

2000kVA transformer and 600 VAC are on one pad and 15kV swithboard is on separate pad next to each other.

There is also 600V to 240/120V, 5kVA transfromer fed from 600 VAC Swbd which feeds receptacle and 15kV switchboard space heaters either 120V or 240V single phase.

I have following questions and am really confused:

1. Does the 2000kva transformer 13.2kV side wye has to have system bonding jumper bonding neutral to gnd? If yes then how does that work in transformer or at the 15kV SWBD?

2. Does their need to be neutral to bond at 15kV SWBD 125A fuses since that would be service disconnect?

3. One neutral to bond exists at 600VAC Swbd attached sketch shown does it need any other neutral to bond by code anywhere or need to be relocated? Not sure how this would work. Everything is customer owned.

4. Concentric neutral to transfromer would you need actual separate neutral from 15kV Swbd to 2000kva transfromer or concentric is ok per code?

5. 5kVA 600VAC to 240/120VAC single phase transformer too much fed from 600VAC switchboard? Should it be their by code.

All reference NEC 2014 code please not in other versions of code yet.

 

[Hv&Lv]

I don’t want to get into the NEC discussion on this setup. Quite frankly, I’m not up to code on the Photovoltaic and customer transformer applications.

i do want to weigh in on your question though and how a common Wye Wye transformer is built.

the H1, H2, and H3 bushings on the XF (13.2 side) are elbows as you know. The concentric neutral is normally bonded to the circle ground, which is attached to the ground rod and the H0/X0 bushing on the secondary side. (Should be labeled as such)
The primary winding Wye has an internal jumper that ties to H0/X0

when we terminate the elbows we normally leave about 3 feet of concentric neutral cable to make and bonding connections we need.
If your using one third neutral cable, remember that all three have to end up at the same place. You can’t squeeze them all together and drop two.
if you using full neutral cable like we do, we can squeeze all three together close and just leave one long tail for bonding and grounding.

 

[electrofelon]

Here you go posting the same question again, hoping for more/better responses I guess. It's annoying for me when I take the time to reply, and it's like you never even read what I said. I suggest spending a half hour or so going over that other thread and digesting it for a while. Did you look over those code sections, 250.184??

I will just comment on one of your new questions: note that concentric shield and concentric neutral are not necessarily the same thing . If it is true concentric neutral them yeah that is why it is called concentric NEUTRAL, that is your neutral. For a MGN it's essentially like a service where the neutral/grounded conductor does the bonding and it's also earthed at every piece of equipment.

 

[hhsting]

Post #1 sketch shows utility brings in three phase conductors with concentric neutral. Let me explain below with solar its very confusing:

NEC 2014 Article 250.180 says previous section apply so 250.30 also applies. However, I am not sure which side of 2000kva xfmr is primary and which secondary since 600V swbd has load to 5kVA xfmr. Solar panels inverters would feed 600VAC swbd which then would feed two xfmr 2000kVA and 5kVA xfmr and would make 2000kVA xfmr 600VAC primary. However during night time or when solar panels are not producing at all the utility would feed the 2000kVA xfmr which then would feed 600VACswbd which then would feed 5kVA xfmr load making 2000kVA 13.2kV side primary.

Now going back I am not sure if system is Single Point Grounded Neutral System or Multigrounded Neutral System. Based on what is being said previous post need to coordinate with utility but they are not saying anything. I read and re read the post but I am still very confused as to how to properly ground and bond with solar involved per code. So lets take both scenarios:

1. Single Point Grounded Neutral System the utility is providing three phase conductors with concentric neutral no equipment grounding conductor to 15kV Swbd. I would place the concentric neutral on neutral bar and provide ground bar, grounding electrode conductor to electrodes and main bonding jumper at 15kV Swbd. From 15 kV swbd would carry neutral, three phase conductors, EGC to 2000kVA xfmr 13.2kV wye side. Now which side is primary and which is secondary depends on inverter are on or off. Do I again bond neutral to ground in the 2000kVA xfmr 13.2kV side? Once I get to the 600VAC side of 2000kVA xfmr wye do i again do neutral to bond their? Also primary and secondary depends on inverter assume 600VaC is primary then i have system bonding jumper at xfmr and then on secondary 13.2kV SWBD again main bonding jumper?

2. Multigrounded Neutral System the utility is providing three phase conductors with concentric neutral no equipment grounding conductor to 15kV Swbd. I would connect grounding electrode conductor to concentric neutral and other end to electrode. Would run three phase conductors and neutral but their would NOT be equipment grounding conductor from 15kV Swbd to 2000kVA xfmr 13.2kV side where again the neutral would have grounding electrode conductor to electrode. Going to 600Vac side 2000kVA xfmr the neutral would have to be grounded with grounding electrode conductor to electrode again. From the neutral I would do system bonding jumper to equipment grounding bar which then would feed 600VAC swbd. However then again if inverters and solar panels are on 600VAC is primary but not sure if system bonding jumper exists in primary or not so as long as its wye it has to have system bonding jumper? Also post #1 attachment shows equipment grounding conductor and grounding at each 13.2kV equipment how is that multigrounded neutral?


Please correct me if I am wrong above. What is proper way of doing this per code?

 

[ggunn]

<content deleted> Never mind. I don't know much about MV.

 

[jaggedben]

I don't know anything about MV, but I'll offer this comment: stop letting the solar confuse you. The utility side of the transformer is still the 'primary' for most important considerations. It energizes the transformer and almost certainly has higher fault current available. The solar inverter manufacturer may have some input into what kind of transformer is used, but the bonding and grounding rules for an SDS do not change whatsoever just because it connects a solar system.

 

[electrofelon]

Who designed this? Can you ask them? I don't see anything wrong with the drawing, but it's very hard to read. It does not appear to be an MGN and seems like they are not providing a neutral conductor. I'll try to look over it later on a larger screen. Take a look at 250.186(B) that may be what is going on . You need to find out from the utility if the serving system is grounded or not and what conductors they are supplying. FYI I am not very familiar with MV either, but everything you need relating to your questions should be found in part x of 250.

 

[hhsting]

I have broken the post #1 attachment into two parts so that it is now zoomed in so that you can see better.

 

[ggunn]

Is there a reason why you are going wye - wye instead of wye - delta? When we are connecting to 208V 3P or 480V 3P through a transformer we usually connect to the service with the delta side of a wye - delta.

 

[electrofelon]

Is there a reason why you are going wye - wye instead of wye - delta? When we are connecting to 208V 3P or 480V 3P through a transformer we usually connect to the service with the delta side of a wye - delta.

Yeah that is odd and what threw me off. When he said "wye wye" I assumed it was an MGN system as that is what I have always seen the utilities do. It's odd to have a wye primary with the point floating and isolated for that type of transformer. I wonder if they just figured that would be a common transformer and they would just remove the wye point to ground bonding strap. But I agree I would have defaulted to a Delta wye. But again, I am not an MV guy, maybe it's like that for a reason that is above my paygrade.

 

[hhsting]

There are no MV guys over here. This is solar farm and solar panels are outside on acre of land no building. I am reviewer of this for AHJ and so I review if everything is per code or not. You are saying primary utility side is typically delta so 13.2kV is delta not wye from utility? I thought it could be wye or delta. I am not the designer so i am not sure why wye is primary. However, I intend to and will ask the designer this question and let you know.

In the meantime if we can please go back to question and situation post #4 how does one ground properly post #8 attachment per code?

 

[tortuga]

1. Does the 2000kva transformer 13.2kV side wye has to have system bonding jumper bonding neutral to gnd?

No the drawing shows an ungrounded utility system, 250.186(B)

2. Does their need to be neutral to bond at 15kV SWBD 125A fuses since that would be service disconnect?

There is no neutral at that point, the system is ungrounded and not required to be grounded but permitted to be
250.20(C)

3. One neutral to bond exists at 600VAC Swbd attached sketch shown does it need any other neutral to bond by code anywhere or need to be relocated? Not sure how this would work. Everything is customer owned.

600VAC wye system is required to be grounded,
250.20(B)(2)
Switchboard is a separately derived system grounding / bonding location 250.30(A)(1).
This is interesting :

the H1, H2, and H3 bushings on the XF (13.2 side) are elbows as you know. The concentric neutral is normally bonded to the circle ground, which is attached to the ground rod and the H0/X0 bushing on the secondary side. (Should be labeled as such)
The primary winding Wye has an internal jumper that ties to H0/X0

when we terminate the elbows we normally leave about 3 feet of concentric neutral cable to make and bonding connections we need.
If your using one third neutral cable, remember that all three have to end up at the same place. You can’t squeeze them all together and drop two.
if you using full neutral cable like we do, we can squeeze all three together close and just leave one long tail for bonding and grounding.

4. Concentric neutral to transformer would you need actual separate neutral from 15kV Swbd to 2000kva transfromer or concentric is ok per code?

They will need to show compliance with 250.190(C)(2)

5. 5kVA 600VAC to 240/120VAC single phase transformer too much fed from 600VAC switchboard?

Bussbars in the switch gear are still outside feeder conductors and have to be sized to the calculated load per 225.5
We would need to see the load calc.

There has been some helpful info on here before as to the why of a wye - wye:
https://forums.mikeholt.com/forum/ac...ormer?t=138605
https://apps.geindustrial.com/publib...-3388B|generic

EDIT: 2014 Code references.
Hope this helps
Cheers

 

[electrofelon]

No the drawing shows an ungrounded utility system, 250.186(B)

​​​​​​I disagree. We cannot tell if that is an ungrounded utility system. In fact that code reference is for grounded systems, but where Poco does not provide a grounded conductor. OP needs to find out f I'm POCO what kind of system this is

 

[ggunn]

​​​​​​I disagree. We cannot tell if that is an ungrounded utility system. In fact that code reference is for grounded systems, but where Poco does not provide a grounded conductor. OP needs to find out f I'm POCO what kind of system this is.

Yes. Just because the POCO is not supplying a neutral, that does not mean that the voltages on the phases are not referenced to ground.

The reason I asked about wye - wye rather than wye - delta is that with 208V and 480V primaries, wye - delta transformers are more readily available than wye - wye. The way the transformer is shown is essentially a wye - delta connection anyway, since the N terminal on the primary is unconnected; maybe with MV transformers wye - wye is more common, I dunno.

 

[electrofelon]

Yes. Just because the POCO is not supplying a neutral, that does not mean that the voltages on the phases are not referenced to ground.

The reason I asked about wye - wye rather than wye - delta is that with 208V and 480V primaries, wye - delta transformers are more readily available than wye - wye. The way the transformer is shown is essentially a wye - delta connection anyway, since the N terminal on the primary is unconnected; maybe with MV transformers wye - wye is more common, I dunno.

In my experience, if it's a wye MGN distribution, it will be a wye wye transformer with both primary and secondary neutrals landed and bonded together. I dont know all the specifics of all that. Some of it I have forgotten and honestly a lot of it is above me. The old paper "the why's of the wyes" which has been referenced, has lots of info. I don't know the design considerations for NOT bringing the primary neutral to the transformer, and if so whether changing the primary to a Delta is appropriate. I think ferroresonance is a consideration and it is less of a concern with a wye connection.

There is lots of Delta distribution here in central NY, but I've never gotten a close look at padmounts for these.

 

[hhsting]

P

In my experience, if it's a wye MGN distribution, it will be a wye wye transformer with both primary and secondary neutrals landed and bonded together. I dont know all the specifics of all that. Some of it I have forgotten and honestly a lot of it is above me. The old paper "the why's of the wyes" which has been referenced, has lots of info. I don't know the design considerations for NOT bringing the primary neutral to the transformer, and if so whether changing the primary to a Delta is appropriate. I think ferroresonance is a consideration and it is less of a concern with a wye connection.

There is lots of Delta distribution here in central NY, but I've never gotten a close look at padmounts for these.

Post #3 concentric neutral is your neutral but does NEC recoginize this. So if their is concentric neutral to 125 fuse in 15kv sWBd then utility must bring concentric neutral at point of interconnection no?

 

[electrofelon]

P
Post #3 concentric neutral is your neutral but does NEC recoginize this. So if their is concentric neutral to 125 fuse in 15kv sWBd then utility must bring concentric neutral at point of interconnection no?

You also threw me off mentioning "concentric neutral". There does not appear to be a MV neutral on your drawing. Just to be clear, note that you might be using "concentric neutral cable" but not using the neutral conductor if there is no neutral. For example utilities will typically use concentric neutral cable for everything, even if the system is ungrounded and has no neutral. In those cases I believe the outer conductor is used as a bonding/grounding conductor.

 

[hhsting]

Yes. Just because the POCO is not supplying a neutral, that does not mean that the voltages on the phases are not referenced to ground.

The reason I asked about wye - wye rather than wye - delta is that with 208V and 480V primaries, wye - delta transformers are more readily available than wye - wye. The way the transformer is shown is essentially a wye - delta connection anyway, since the N terminal on the primary is unconnected; maybe with MV transformers wye - wye is more common, I dunno.

The inverter that is being used is wye not delta so that side has to be wye. The inverter instruction says the following which says either wye or delta for utility side see attached.

 

[hhsting]

You also threw me off mentioning "concentric neutral". There does not appear to be a MV neutral on your drawing. Just to be clear, note that you might be using "concentric neutral cable" but not using the neutral conductor if there is no neutral. For example utilities will typically use concentric neutral cable for everything, even if the system is ungrounded and has no neutral. In those cases I believe the outer conductor is used as a bonding/grounding conductor.

Post #8 MV Gear Part 2.pdf attachment clearly says with arrow point to cable 3#1 AWG 15kV MV 90 with concentric neutral transformer 13.2kV side which continues to MV Gear Part 1.pdf attachment 15kV gear:

 

[electrofelon]

Right, they may just be using that because it's super common, doesn't mean its a grounded system with a neutral.....but there appears to be a ground wire (SSBJ) going to the utility which implies it is, 250.86(B) . You need clarification from the utility what kind of system it is, and the designer about the grounding connections. Often not all grounding connections are shown on drawings.