277V Corner Grounded Delta

[knuckles1978]

Hey there, I'm new to the forum so I do apologize if this is posted inthe wrong area. I was recently asked to look over a friends panel in an olderSt. Louis city repair garage for installation of a piece of equipment. Themachine which he would like to install requires a 3phase 480V Wye infeed @roughly 60A. The 200A 3phase panel in this building, which is currently notbeing used by any other devices, has a 277V corner grounded delta infeed. Ihave ran into this in a couple of other circumstances however did not create anissue with the task at hand. In this instance though, considering he needs toget this to the desired 480V outfeed, I have been thrown a little off track!Haha. After much searching, finding a transformer solely for this purpose doesnot seem to be a cost effecient option, and pretty much not an option at all.My next though was perhaps to set him up with a auto-transformer bank to stepthe infeed down to 240V, then run through a transformer to get to 480V. Thequestion here though is, will that grounded leg present a problem attempting togo this route? Does anyone have a better solution to this that I'm possiblyoverlooking? I'm sure by this point I have completely over-complicated thesituation, so I am turning to you guys (and gals) for any and all help andassistance you can provide. For those unfamiliar with thisefficient yet pesky set up, it is a 3 wire set up that reads 277V across legs and 277V to ground on twolegs, yet 0V to ground on "B" leg. Yep, fun times! Thanks in advance.

Todd

 

[Smart $]

My recommendation is to talk with the POCO about making this into a 480Y/277V service. Of course you'll have to make sure the customer side is up to snuff as a 480Y/277V service.


Welcome :thumbsup:

 

[don_resqcapt19]

Todd,
Can you explain the supply system a little more? No standard transformer will give you 277 phase to phase. Corner grounded deltas will normal be 240 or 480 phase to phase and phase to ground. 277 normally only exists as line to neutral voltage on a 480 volt wye system.

 

[iceworm]

Todd -
What you have described is definitely a 277V corner grounded delta. That's one I have never heard of before - never ever. I am absolutely not familiar with this configuration. I can't think of what one could even use it for. There are no motors made to fot that. I guess one could connect lighting to it. But you could only use two legs. You could not connect lighting across the two hot legs. I can see why the existing panel has nothing fed from it.

I can't help with your question. I can't think of anything to do to use the existing system other than to get a custom wound transformer. However i do have a couple of curiousity questions:

Your post says you have run into this a few times before. That's amazing. What were the applications on the others?

Since this panel is unused, what is powering up the shop? What is the other service to the shop?

Does anyone at the POCO or any old timers around the shop know what this was ever used for?

ice

 

[Smart $]

... I guess one could connect lighting to it. But you could only use two legs. You could not connect lighting across the two hot legs. ...

Why not? I believe one could.

I'm of the impression POCO provided this as 277V open delta, and most likely for 277V lighting.

Shouldn't be too hard to reconfigure a 480V wye-wye isolation transformer. You'd just have to isolate the primary winding leads for individual phase connections rather than have an H0. But it'd be better still to have POCO reconfigure their transformers.

 

[iceworm]

... You could not connect lighting across the two hot legs. ...

Why not? I believe one could. ...

Because Llighting is required to to listed. Listed means one follow the instructions. 277V lighting is designed for a grounded system where the connection is to a hot and a neutral.

I started my post with, "I can't help ..." - cause I can't. This 277V open D you speak of - I'm sure it exists. However, it appears to me to be somewhere between insane and moron.

QUOTE=iceworm;1387635]... Shouldn't be too hard to reconfigure a 480V wye-wye isolation transformer. ...[/QUOTE]
Truely an interesting idea. Let's see, take an off the shelf 480Y/480Y, 225kva (you might get by with a 150kva), rip the covers off, cut the primary windings loose, reconnect for 277D. I think that is called a custom transformer. And getting an off the shelf 480 Y-Y may not be a quick thing. I suspect they are not on the shelf.

You are completely correct about doing the work on the internal panels - there are no loads connected to the panel. That does make it easier to shred everything and put back with out disturbing the rest of the shop.

Following your comment, my inclination is also to ask the utility what they want to get a 480Y service. And I am still curious about the other service to the shop. But none of this is any help to the OP questions.

ice

 

[Smart $]

Because Llighting is required to to listed. Listed means one follow the instructions. 277V lighting is designed for a grounded system where the connection is to a hot and a neutral.

Perhaps some. BTW, this is a grounded system. There are multi-tap ballast units, which can be 480V, 240V, or 208V, in addition to 277V, all of which are Line-to-Line connections. It is not required that a grounded conductor be connected to the Common of the ballast input leads.

I started my post with, "I can't help ..." - cause I can't. This 277V open D you speak of - I'm sure it exists. However, it appears to me to be somewhere between insane and moron.

You are entitled to your opnion...

... Shouldn't be too hard to reconfigure a 480V wye-wye isolation transformer. ...

Truely an interesting idea. Let's see, take an off the shelf 480Y/480Y, 225kva (you might get by with a 150kva), rip the covers off, cut the primary windings loose, reconnect for 277D. I think that is called a custom transformer. And getting an off the shelf 480 Y-Y may not be a quick thing. I suspect they are not on the shelf.

I didn't say it wouldn't be a custom transformer (doesn't matter who is doing the customization). Also, I can't say for certain a 480Y-Y is a shelved transformer (depends on whose shelf you are talking about), but I do know it is a commonly sold configuration, and I could have one (not yet customized) on site in less than two weeks.

 

[Hv&Lv]

I have never built a 277V corner grounded delta bank. Wait, maybe I have. The L-L voltages are 480...
I am like some others here, confused as to why, and especially how, a bank could be built that only gives 277V (L-G) without 480(L-L). I have connected one 277/480 Xf to control 277V lights at a ball field though. of course, it still gives you 480 single phase.

 

[Smart $]

...
I am like some others here, confused as to why, and especially how, a bank could be built that only gives 277V (L-G) without 480(L-L). I have connected one 277/480 Xf to control 277V lights at a ball field though. of course, it still gives you 480 single phase.

How do you build a 480Y/277V service out of three transformers?

Take one transformer away and reverse the secondary connections of just one of the remaining two. 277V open delta.

Put the third transformer back, with secondary connections configured properly across open terminals, and you get full 277V delta.

 

[iceworm]

Perhaps some. BTW, this is a grounded system. There are multi-tap ballast units, which can be 480V, 240V, or 208V, in addition to 277V, all of which are Line-to-Line connections. It is not required that a grounded conductor be connected to the Common of the ballast input leads. ...

Perhaps all. I specifically said 277V, not multi-tap. However, you are correct. Any multitap that includes 208, or 480, and 277 should work on 277V with two hot leads.

... You are entitled to your opnion. ...

Agree or disagree - it doesn't realy matter. But it is more useful if you back it up with a reasoned argument. In my opinion (you know, the one that I am entitled to that's the difference between "entitled opinion" and good engineering.

... BTW, this is a grounded system. ...

Yes - and ...? The OP knew that. I knew the OP alluded to that. I assumed you knew that. I assumed you knew that I assumed that you knew that. And I assumed that .... (I'm poking fun - okay, I'll quit)

... but I do know it is a commonly sold configuration 480Y - Y, and I could have one (not yet customized) on site in less than two weeks.

Maybe. I have never seen one in 45 years. I have never seen an application where one would want one in 45 years. I'd be curious as to how you know this is a "commonly sold configuration". Have you ever seen one? Have you ever designed a system where one was needed? Have you ever bought one? If so what were the applictions?

None of this means they don't exist on-the-shelf. I just means I won't put any faith in your statement about two week availability without calling and getting a quote. I suspect the only one that one would find is used and (selling for scrap, or the mfg winds when you order it.

Corner grounded 277D just looks useless. I can not think of any appliction that is not better served by some other system

ice

 

[iceworm]

I have never built a 277V corner grounded delta bank. ...

Hv -
I'm really glad to hear that. You appear to have a lot of time with utilities. I suspect you have seen most every type of screwed up sustem there is.
And this is not one of them That is good. This is an infection that needs to be contained.

The only one that comes to mind is if one started with 4160D - 480D and changed out the primary to 2400V, that would give a 277D secondary. That seems pretty far fetched that a utility would do that on purpose. Thank God the ones I work with aren't that moronic.

How do you build a 480Y/277V service out of three transformers?

Take one transformer away and reverse the secondary connections of just one of the remaining two. 277V open delta.

Put the third transformer back, with secondary connections configured properly across open terminals, and you get full 277V delta.

Smart -
Yes, one could do this. I would question why one would take a three perfectly good transformers and purpously connect to get a near useless voltage system. Especially when one could just as easy get 480Y secondary.

 

[Hv&Lv]

How do you build a 480Y/277V service out of three transformers?

Take one transformer away and reverse the secondary connections of just one of the remaining two. 277V open delta.

Put the third transformer back, with secondary connections configured properly across open terminals, and you get full 277V delta.

Why would anyone ever do that? What application would this configuration serve? Transformers can be connected in many different ways to give you some wild voltages, but why would you do that just because it is possible? I can connect a multitap ballast for a light to the high leg of an open delta bank at 208 volts, but why? Why make it harder than it needs to be on purpose?

 

[Smart $]

...
Maybe. I have never seen one in 45 years. I have never seen an application where one would want one in 45 years. I'd be curious as to how you know this is a "commonly sold configuration". Have you ever seen one? Have you ever designed a system where one was needed? Have you ever bought one? If so what were the applictions?

None of this means they don't exist on-the-shelf. I just means I won't put any faith in your statement about two week availability without calling and getting a quote. I suspect the only one that one would find is used and (selling for scrap, or the mfg winds when you order it.

I've seen one. It was used to isolate power between a solidly grounded system and one with high impedance ground. I do not design systems, so that issue is moot. I admit the two week lead was surmised... but just to offer some proof for built to order:

http://www.google.com/products?sour...bution+Transformer+480V+Wye+Pri+480Y/277V+Sec

Corner grounded 277D just looks useless. I can not think of any appliction that is not better served by some other system

I do not disagree... but the existence of such according to OP makes it worthy of discussion at the very least.

 

[iceworm]

I've seen one. 480Y-YIt was used to isolate power between a solidly grounded system and one with high impedance ground. .

Hummm ... Should have been a 480D-Y. I've put in a lot of thso just for the purpose you listed.

... I do not disagree... but the existence of such according to OP makes it worthy of discussion at the very least.

Yes, tht's true. I wish I could help - but I can't. But, I still am curious about are my original questions.

Your post says you have run into this a few times before. That's amazing. What were the applications on the others?

Since this panel is unused, what is powering up the shop? What is the other service to the shop?

Does anyone at the POCO or any old timers around the shop know what this was ever used for?

ice