Wye to wye questions

[hhsting]

It is a balanced three phase system and so no current in the neutral during normal operation. Any current in neutral due to any unbalance fault may be rectified rather quickly as it is a technically supervised installation. Bonding of transformer neutrals on both sides to ground (back to respective sources) is required for proper protection of Y-Y transformer (operation of protective device) in the OP case.

Attahced sketch shows two options one MGN and second single point ground. Since X0 and H0 are bonded neutral are grounded both sides in either option. Kind of like 3 pole ATS neutral not switched for generator that is wye but its transformer. If not then I am not sure what you mean?

 

[ggunn]

I'm no expert at MV, and if that changes things please clue me in, but it seems to me that since X0 and H0 are bonded in the transformer there should be one and only one neutral to ground bond anywhere in either drawing.

 

[Hv&Lv]

I'm no expert at MV, and if that changes things please clue me in, but it seems to me that since X0 and H0 are bonded in the transformer there should be one and only one neutral to ground bond anywhere in either drawing.

Kinda what I figure...one and only one
like I’ve posted before, we do this everyday and there is only one point, that’s the concentric neutral.
live posted a time or two about one third vs full neutral cable and the connections...
shielded cable is a different story, but he has posted in three different threads about concentric neutral and connection points.

seems like I menti9ned the X0 and H0 being interconnected internally about 80 posts ago...

 

[hhsting]

I'm no expert at MV, and if that changes things please clue me in, but it seems to me that since X0 and H0 are bonded in the transformer there should be one and only one neutral to ground bond anywhere in either drawing.

.

Kinda what I figure...one and only one like I’ve posted before, we do this everyday and there is only one point, that’s the concentric neutral.
live posted a time or two about one third vs full neutral cable and the connections...
shielded cable is a different story, but he has posted in three different threads about concentric neutral and connection points.

seems like I menti9ned the X0 and H0 being interconnected internally about 80 posts ago...

@ ggunn and H&Lv: Their is only one option #1 N to G at 600V swbd however option #1 is MGN and concentric neutral cable needs to be grounded at 13.2kV side of transformer and 13.2kV swbd and 13.2kV equipment bonded thru concentric neutral cable. N to G is not at the service disco do you consider concentric neutral cable grounded at service disco second N to G or per 250.24(B) N to G should be at service disco only not at 600V swbd since this is not SDS rules of 250.30 do not apply in that case 600VAC system require EGC not just neutral right so MGN cannot be applied in this install? Not sure what you mean?

Option #2 N to G only at 13.2kV swbd but its single point so all equipment bonded thru EGC.

If not then not sure what you mean?

@H&Lv: 80 posts ago it wasnt sure but suspected that it should be one of them was you who mentioned. Xfmr nameplate was attached few posts ago confirming along with few unanswered question after discussion with engineer.

 

[ggunn]

@ ggunn and H&Lv: Their is only one option #1 N to G at 600V swbd however option #1 is MGN and concentric neutral cable needs to be grounded at 13.2kV side of transformer and 13.2kV swbd and 13.2kV equipment bonded thru concentric neutral cable. N to G is not at the service disco do you consider concentric neutral cable grounded at service disco second N to G or per 250.24(B) N to G should be at service disco only not at 600V swbd since this is not SDS rules of 250.30 do not apply in that case 600VAC system require EGC not just neutral right so MGN cannot be applied in this install? Not sure what you mean?.

I'm not quite sure what you are saying, either, but any time you have two neutral to ground bonds in the same system, it provides parallel paths for neutral current split between the neutral and ground conductors, and you can't do that. As far as I know the code does not make an exception for an ostensibly balanced system where no neutral current is anticipated. That's with the caveat that I don't know much about MV and if that changes things please pardon my ignorance.

 

[hhsting]

Post #81 attachments where do you or anyone see two neutral to ground?

 

[ggunn]

Post #81 attachments where do you or anyone see two neutral to ground?

In Option 1 it looks to me like there are three: one in each disco and one in the transformer, so you are correct, there are not two.

 

[hhsting]

Primary side of the transformer 13.2kV is concentric neutral cable and that is grounded 250.184(C) their is no EGC. Main bonding jumper is at 600V swbd. Since xfmr is not SDS, I do see that the main bonding jumper can only be at service disco not in compliance with 250.24(B) which is 13.2kv swbd option #2 which is 250.184(B) which means 250.184(C) cannot apply to this install only 250.184(B). Can some Hv&Lv or electrofelon or any one familiar with this sort of installation let me know?

 

[Sahib]

Attahced sketch shows two options one MGN and second single point ground. Since X0 and H0 are bonded neutral are grounded both sides in either option. Kind of like 3 pole ATS neutral not switched for generator that is wye but its transformer. If not then I am not sure what you mean?

Option 2 is a valid one. Bond the POCO neutral also to the common point which otherwise would cause floating neutral with respect to POCO supply.

 

[electrofelon]

I'm no expert at MV, and if that changes things please clue me in, but it seems to me that since X0 and H0 are bonded in the transformer there should be one and only one neutral to ground bond anywhere in either drawing.

Clearly the NEC is geared toward making N-G separate as soon as possible. For MV, we have been discussing the MGN provision (250.184(C)) which allows equipment to be connected the N at more than one location. I do not know why this is allowed for MV but not for LV.

For LV there are a few loopholes, notably existing range and dryer circuits, and 250.30(A)(1) exception 2.

 

[electrofelon]

Primary side of the transformer 13.2kV is concentric neutral cable and that is grounded 250.184(C) their is no EGC. Main bonding jumper is at 600V swbd. Since xfmr is not SDS, I do see that the main bonding jumper can only be at service disco not in compliance with 250.24(B) which is 13.2kv swbd option #2 which is 250.184(B) which means 250.184(C) cannot apply to this install only 250.184(B). Can some Hv&Lv or electrofelon or any one familiar with this sort of installation let me know?

I am having a hard time understanding what you are asking. I stand by my "fully correct" option described in the second part of post #71, which is option A in post #75.

 

[Sahib]

Clearly the NEC is geared toward making N-G separate as soon as possible. For MV, we have been discussing the MGN provision (250.184(C)) which allows equipment to be connected the N at more than one location. I do not know why this is allowed for MV but not LV.

For easy passage of lightning discharge to ground as there may not be separate ground wire for MV in exposed outdoor locations.

 

[GoldDigger]

One potential reason for multiple grounds on MV is that at that voltage the resistance of a not particularly good earth ground electrode can be a fault clearing path.
Among other things, if a line incident interrupts the neutral as well as dropping the ungrounded line(s), a ground connection in the isolated neutral section can help clear a fault.

Sent from my XT1585 using Tapatalk

 

[Sahib]

The ground resistance of MGN is often less than 1 ohm.

 

[hhsting]

I am having a hard time understanding what you are asking. I stand by my "fully correct" option described in the second part of post #71, which is option A in post #75.

What I meant was in post #70 attachment uses MGN and service point for incoming utility concentric neutral cable is in line side of 13.2kV Swbd service breaker, downstream xfmr is not SDS however N to G bond is in 600V swbd is it a violation of NEC 2014 Article 250.24(B): N to G bond has to be at service disco i.e at 13.2kV Swbd?

 

[hhsting]

One potential reason for multiple grounds on MV is that at that voltage the resistance of a not particularly good earth ground electrode can be a fault clearing path.
Among other things, if a line incident interrupts the neutral as well as dropping the ungrounded line(s), a ground connection in the isolated neutral section can help clear a fault.

Sent from my XT1585 using Tapatalk

In my case the 13.2kV Swbd is on concrete pad and right next to it I have another concrete pad which has 2000kva xfmr and 600V swbd i.e all equipment are short distances from each other. Sourrounding both concrete pads is a ground ring. In the MGN scenario 13.2kV at swbd and xfmr neutral has GEC to same one grounding electrode the ground ring.

If I understand your post correctly then each equipment has to have different grounding electrodes?

 

[GoldDigger]

In my case the 13.2kV Swbd is on concrete pad and right next to it I have another concrete pad which has 2000kva xfmr and 600V swbd i.e all equipment are short distances from each other. Sourrounding both concrete pads is a ground ring. In the MGN scenario 13.2kV at swbd and xfmr neutral has GEC to same one grounding electrode the ground ring.

If I understand your post correctly then each equipment has to have different grounding electrodes?

I am not saying that.

I am saying that it is allowed to do that, since the POCO setup is MGN, unlike what the NEC allows for low voltage. And that there may be some benefit to doing that. It may or may not be required by specific POCO design rules.

 

[hhsting]

I am having a hard time understanding what you are asking. I stand by my "fully correct" option described in the second part of post #71, which is option A in post #75.

What I meant was in post #70 attachment uses MGN and service point for incoming utility concentric neutral cable is in line side of 13.2kV Swbd service breaker, downstream xfmr is not SDS however N to G bond is in 600V swbd is it a violation of NEC 2014 Article 250.24(B): N to G bond has to be at service disco i.e at 13.2kV Swbd?

 

[Sahib]

What I meant was in post #70 attachment uses MGN and service point for incoming utility concentric neutral cable is in line side of 13.2kV Swbd service breaker, downstream xfmr is not SDS however N to G bond is in 600V swbd is it a violation of NEC 2014 Article 250.24(B): N to G bond has to be at service disco i.e at 13.2kV Swbd?

The design is to supply power from your side to POCO. So POCO side is load side in your case and 600V SWbd is 'service board'.

 

[electrofelon]

What I meant was in post #70 attachment uses MGN and service point for incoming utility concentric neutral cable is in line side of 13.2kV Swbd service breaker, downstream xfmr is not SDS however N to G bond is in 600V swbd is it a violation of NEC 2014 Article 250.24(B): N to G bond has to be at service disco i.e at 13.2kV Swbd?

I think I already gave some plausible justification for that N-G bond in the 600V switchboard: 1) Call it an SDS (which IMO is a silly distinction that a field installed connection doesnt make it an SDS where has factory installed does) 2) use 250.30(A)(1) exception 2. As I said, this is not fully correct and may be a stretch to some people.