NO V To G

[solaeros]

So, anyone ever seen a 3 phase Delta xformer, where you cannot read voltage on 1, phase to ground on the load side, while the other two phases read just fine; and all three primary phases read to ground? I would have thought the transformer had lost a leg. However all the machinery running off this transformer was operating properly

 

[mdshunk]

Sounds just like corner grounded delta.

 

[solaeros]

I'm guessing your right on the money (I wasn't able to get into the transformer housing to see for sure. Is this a very common practice? I've only been in the business about 7 years and haven't come across it before. It seems counter intuitive to wire 3 phase motors to a leg that's grounded (essentialy a neutral) I guess the inductive reactance will keep it from harm just like a light bulb would on 120 or 277v

 

[mdshunk]

Is this a very common practice?

Depends on the transformer. Gotta ground something. Sometimes you only have one corner of the delta as your only choice.

 

[76nemo]

I'm guessing your right on the money (I wasn't able to get into the transformer housing to see for sure. Is this a very common practice? I've only been in the business about 7 years and haven't come across it before. It seems counter intuitive to wire 3 phase motors to a leg that's grounded (essentialy a neutral) I guess the inductive reactance will keep it from harm just like a light bulb would on 120 or 277v

Ahhhh, corner grounded, here we go again,.............

 

[augie47]

or

or

It is also possible that you have an ungrounded delta system in which one phase has gone to ground unintenionally. If the design is for ungrounded, I would suggest you look into a ground detection system.

 

[mdshunk]

Just thought I should add that if you're gonna be working on this thing, it takes special disconnects and breakers. You can't fuse the grounded conductor, as one for instance. Square D has a little summary: http://ecatalog.squared.com/pubs/Ci...lded Case Circuit Breakers/2700DB0202R606.pdf

 

[mdshunk]

It is also possible that you have an ungrounded delta system in which one phase has gone to ground unintenionally. If the design is for ungrounded, I would suggest you look into a ground detection system.

Yikes, didn't really think of that. When I hear hoof beats, I normally think of horses, but I suppose that it is possible he's dealing with zebras.

 

[Pierre C Belarge]

Yikes, didn't really think of that. When I hear hoof beats, I normally think of horses, but I suppose that it is possible he's dealing with zebras.

Marc
could you explain that sentence?

 

[mdshunk]

Marc
could you explain that sentence?

I'd be glad to, but it's a pretty old expression.

When you hear hoofbeats, think horses and not zebras. Also known as Occam's Razor. It's just logical troubleshooting. We call it K.I.S.S. now.

Some people automaticly think the root of every problem is the most complicated, exotic, and wildest thing they've ever heard of. Check the common, simple stuff first, then move on to the more exotic if need be. Take a tylenol for your headache before you go for a CAT scan.

 

[jrannis]

I'd be glad to, but it's a pretty old expression.

When you hear hoofbeats, think horses and not zebras. Also known as Occam's Razor. It's just logical troubleshooting. We call it K.I.S.S. now.

Some people automaticly think the root of every problem is the most complicated, exotic, and wildest thing they've ever heard of. Check the common, simple stuff first, then move on to the more exotic if need be. Take a tylenol for your headache before you go for a CAT scan.

I thought it ment that most people thought of horses first, then found it to be zebras.

 

[jrannis]

So, anyone ever seen a 3 phase Delta xformer, where you cannot read voltage on 1, phase to ground on the load side, while the other two phases read just fine; and all three primary phases read to ground? I would have thought the transformer had lost a leg. However all the machinery running off this transformer was operating properly

Is the installation only for the machinery?
The first phase to ground is free, its the second on that causes all of the problems.

 

[don_resqcapt19]

Marc,

Just thought I should add that if you're gonna be working on this thing, it takes special disconnects and breakers.

In many cases you can use single phase equipment for this application. You have to check the listing and make sure that you don't use "slash" rated breakers.
Don

 

[LarryFine]

I thought it ment that most people thought of horses first, then found it to be zebras.

It seems more logical to think that the ones who think "horses" are more likley to be correct than those who think "zebras" are.

 

[steve66]

It seems more logical to think that the ones who think "horses" are more likley to be correct than those who think "zebras" are.

Agreed, for anyone in Kentucky. However, anyone that lives in Africa might see it different

 

[brian john]

Just out of curiosty what is the primary voltage? and configuration wye? delta?

 

[LarryFine]

Just out of curiosty what is . . . configuration wye? delta?

I can answer this half.

So, anyone ever seen a 3 phase Delta xformer . . .

 

[benaround]

And it is grounded.

 

[iaov]

I'd be glad to, but it's a pretty old expression.

When you hear hoofbeats, think horses and not zebras. Also known as Occam's Razor. It's just logical troubleshooting. We call it K.I.S.S. now.

Some people automaticly think the root of every problem is the most complicated, exotic, and wildest thing they've ever heard of. Check the common, simple stuff first, then move on to the more exotic if need be. Take a tylenol for your headache before you go for a CAT scan.

I always called this Zebra Hunting. I thought I made it up but apparently not. I used to work with a guy who was a cronic zebra hunter. His first guess was always that the machine "lost the program". In 18 years I never once saw a machine lose the program. (I did once see a Reliance PLC lose its OS) Experience has taught me that the problem is almost always a horse and that horse is usualy mechanical not electrical.:smile: