Wye or Delta

[brian john]

I was asked a question today I was not sure about.

Customer has a 3-phase 4-wire wye distribution system from the utility and generator to the ATS from the load of the ATS everything in this facility is 3-phase 3-wire. On his drawings it is state 3-phase 4-wire wye to the ATS and after the ATS the distribution is marked 3-phase 3-wire Delta.

While the utilization equipment may be Delta connected is the distribution properly designated Delta?

 

[barbeer]

Sounds like something was confused along the way somewhere. While you could "transform" wye into delta, it does not just magically happen?

 

[charlie b]

I think the way you do this is to bring the neutral wires to the line side of the ATS, and not connect neutral wires to the load side of the ATS.

The distinction between delta and wye is only relevant to the wiring internal to the transformer (or the generator). Once you leave the source, if you bring only three wires with you, then the distribution system is going to behave as though the source were connected delta.

 

[barbeer]

Do voltages change and such?

 

[dereckbc]

I think the way you do this is to bring the neutral wires to the line side of the ATS, and not connect neutral wires to the load side of the ATS.

The distinction between delta and wye is only relevant to the wiring internal to the transformer (or the generator). Once you leave the source, if you bring only three wires with you, then the distribution system is going to behave as though the source were connected delta.

I agree with Charlie in part except for:

Once you leave the source, if you bring only three wires with you, then the distribution system is going to behave as though the source were connected delta.

If the source is grounded and configured as Wye, faults on the Delta side of the distribution behave the same as any Wye system, you get a failure from over-current protection device operation. A true Delta system is uneffected by a single ground fault.

 

[brian john]

I guess my question is, would you be correct referring to this a 3-wire wye?

 

[dereckbc]

I guess my question is, would you be correct referring to this a 3-wire wye?

Yes it would, 3-wire plus ground

 

[weressl]

I was asked a question today I was not sure about.

Customer has a 3-phase 4-wire wye distribution system from the utility and generator to the ATS from the load of the ATS everything in this facility is 3-phase 3-wire. On his drawings it is state 3-phase 4-wire wye to the ATS and after the ATS the distribution is marked 3-phase 3-wire Delta.

While the utilization equipment may be Delta connected is the distribution properly designated Delta?

Is the generator 3 wire or 4 wire?

It is redundant to call ordinary systems 3 wire AND delta, or 4 wire AND wye.

One may choose not to utilize neutral wire of the 4 wire system, in which case you would call it a 3 wire system, even though the source comprises 4 wires.

If the generator is 3 wire, then it is important that you install a grounding transformer for ground fault protection and/or detection.

 

[drbond24]

Ignoring the neutral does not a delta circuit make.

Yes the phase to phase voltage would still be the same, but insert your 3 wire wye into the primary of a delta wound transformer will not work just because the number of leads are the same. The transformer wouldn't explode or anything, but in my (limited) experience, its life would be drastically reduced.

 

[coulter]

Ignoring the neutral does not a delta circuit make..

That's true

... but insert your 3 wire wye into the primary of a delta wound transformer will not work just because the number of leads are the same. The transformer wouldn't explode or anything, but in my (limited) experience, its life would be drastically reduced.

This completely lost me. I know you're not saying one should not feed a 480D/208Y transformer with the three 480 leads of a 480Y system. That would not make any sense at all.

carl

 

[drbond24]

A transformer that is wound for delta does not like wye, regardless of how many wire you have. I'm just saying that if the distribution system in the plant is 3 wire wye, you would have to be careful what type transformers you were using on the floor.

My only experience comes from a contractor that installed a wye-delta transformer when he needed a delta-wye. He just matched up the voltages and didn't pay any attention to the windings. He connected a delta distribution system to the wye primary on the transformer and was asking me why he had seen three transformer failures in a month. I realize that this is the opposite configuration of what we've been talking about, but the same principal applies.

 

[coulter]

...My only experience comes from a contractor that installed a wye-delta transformer when he needed a delta-wye. He just matched up the voltages and didn't pay any attention to the windings. He connected a delta distribution system to the wye primary on the transformer and was asking me why he had seen three transformer failures in a month. I realize that this is the opposite configuration of what we've been talking about, but the same principal applies.

(emphasis is mine)
Not to my knowledge. I've never seen a 480Y/208Y xmfr - I'm sure one could buy one, I've just never seen one installed. Every installation I've ever been around that is fed with 480V, 3ph, D or Y, 480V transformer primaries will be Delta.

Recommend to check your references on this one.

carl

 

[drbond24]

It's entirely possible that I'm wrong; its been known to happen from time to time.

Are you sure that you've seen delta primary transformers fed with 3 wire wye? It seems to me that the phase angle differences and such between delta and wye would at the very least cause extra heating in the windings.

I admit I am fuzzy on the details of the story I told. I think I have it right, but it was 2 years ago and a different job. I am almost positive that the transformer the contractor was using was 480Y-208 delta. He had ordered them special (he had two or three of them) for a specific job and then ended up not using them, so he was trying to find somewhere to get rid of them. He connected a 480 delta source to the primary and wanted to get 208Y from the secondary but the transformer died at least twice.

 

[Pierre C Belarge]

Brian
I will make a stab at this.

Maybe the service is 3phase, 4 wire 208 with the neutral installed to the Transfer swithch (which I am assuming is also the service disconnect) - because the NEC requires a neutral brought to the service. Maybe from the load side he has 3 phase loads only...like I mentioned, a stab in the dark.

The only other idea that I can come up with is he did not explain it properly to you.

 

[drbond24]

Brian
I will make a stab at this.

Maybe the service is 3phase, 4 wire 208 with the neutral installed to the Transfer swithch (which I am assuming is also the service disconnect) - because the NEC requires a neutral brought to the service. Maybe from the load side he has 3 phase loads only...like I mentioned, a stab in the dark.

The only other idea that I can come up with is he did not explain it properly to you.

I like the last option the best. Bad information from the start.

But, does that mean this entire thread was meaningless? Suddenly I feel a lack of purpose...

 

[coulter]

...I am almost positive that the transformer the contractor was using was 480Y-208 delta. He had ordered them special (he had two or three of them) for a specific job and then ended up not using them, so he was trying to find somewhere to get rid of them. ...

I'll bet a cup of yuppie coffee (payable at a location of my choice) he bought them as step-up transformers.

... He connected a 480 delta source to the primary and wanted to get 208Y from the secondary but the transformer died at least twice.

Doesn't this make you wonder how he was going to get 208Y from a 208D winding?

Recommend to let this one go

carl

 

[drbond24]

Doesn't this make you wonder how he was going to get 208Y from a 208D winding?carl

He was not electrically inclined.

Recommend to let this one go

Agreed!

 

[brian john]

Pierre:

It is a 3 phase 4-wire Wye service and generator each with main disconnect. Distribution to loads is 3-phase 3 wire, no neutral pass the ATS

And as one poster noted it may be redundant BUT at least around here everyone ALWAYS says 3-phase 4-wire Wye or 3-phase 3-wire delta. I told my customer that in actuality it was most likely 3-phase 3-wire Wye NOT DELTA. Others at the facility told him I knew not of what I was saying. I prefer/like/need to know what is the right terminology.

 

[coulter]

... Others at the facility told him I knew not of what I was saying. ...

As others have said. It's not Delta. You tell 'em I think you know what you are talking about. I'm sure that will matter.

Pierre:...It is a 3 phase 4-wire Wye service and generator each with main disconnect. Distribution to loads is 3-phase 3 wire, no neutral pass the ATS. ...

Pretty common in industry. No single phase loads, so no need for a neutral. Of course, none of this is news.

...And as one poster noted it may be redundant BUT at least around here everyone ALWAYS says 3-phase 4-wire Wye or 3-phase 3-wire delta. ...

Nothing wrong with redundant. 480 is ambiguous Ungrounded Delta, grounded Delta, Grounded Y, Grounded Y no neutral, impedance grounded Y, 3W Y, 4W Y, 5W Y.

... I prefer/like/need to know what is the right terminology.

I've never seen a term on a dwg to describe stopping the neutral at the first OCPD. Normally it's apparent from other clues - Grounded Y symbol at the xfmr, only three conductor feeders out to MCCs.

If I had to pick a phrase to put on a drawing, I'd suggest, "3wire grounded Y". That way you differentiate from impedance grounded Y. I'd also make sure there was a grounded Y symbol next to the xfmr.

The reason for the differentiation is most of the stuff I work is impedance grounded Y, so there is no neutral brought out past the grounding resistor. So if someone said, "3W Y", I'd probably ask, "Impedance gounded or Solid?"

carl

 

[templdl]

I re-read the posts and there appeared to be a lot of missing information.
Such as:
What was the L-L-L voltage of this so called original delta system?
Was it grounded? If so what were the L-G voltages?

I find it strange to find this information omitted as the voltage itself will most likely be a tell-tail of what the existing system is.