# 3-Phase Identification



## qisdtech (10 mo ago)

Good morning! I just found your forum via google. I am trying to determine if I have 3-phase WYE electricity at a radio transmitter site where we plan to install a new transmitter. The transmitter requires either 3-phase CLOSED Delta or WYE, 240-volt service to operate properly. The transmitter cannot accept open delta or open wye service without voiding the warranty.
The Electric provider tells me this site is 3-phase 120/240 WYE service. They did not specify if it was Open WYE or standard WYE. I am under the impression that 3-phase requires 3 transformers, and the site only has 2.
Is there such a thing is Open WYE? From these pictures below, can someone provide me guidance on what type of electric service this is? There are only 3 conductors on the pole. All the 3-phase I have seen elsewhere has 4 conductors and 3 transformers.

Thanks in advance!
John


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## micromind (Aug 11, 2007)

That's a 120/240 open ∆ system. 2 transformers is a dead giveaway and the connection to the center bushing on one of them means there's 120 available in addition to 240 1Ø and 240 3Ø.


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## 460 Delta (May 9, 2018)

Just like micro said, open Delta, big lighter, and small kicker. This is a setup for a small one or two motor 3 phase, and larger single phase service.


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## qisdtech (10 mo ago)

Thank you for the info! This helps clear up things greatly.


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## splatz (May 23, 2015)

You already have your answer, but in short if there's two transformers and three phase power, it's open. If it's 240/120, it's not wye. 

I am curious why the manufacturer voids the warranty for an open wye or open delta service, they probably have a good reason and may have figured this out the hard way.


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## ScooterMcGavin (Jan 24, 2011)

Also a 120/240 3 phase wye is mathematically impossible so whoever you’re talking to doesn’t know what they’re talking about.


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## oldsparky52 (Feb 25, 2020)

qisdtech said:


> Good morning! I just found your forum via google. I am trying to determine if I have 3-phase WYE electricity at a radio transmitter site where we plan to install a new transmitter. The transmitter requires either 3-phase CLOSED Delta or WYE, 240-volt service to opte properly. The transmitter cannot accept open delta or open wye service without voiding the warranty.
> The Electric provider tells me this site is 3-phase 120/240 WYE service. They did not specify if it was Open WYE or standard WYE. I am under the impression that 3-phase requires 3 transformers, and the site only has 2.
> Is there such a thing is Open WYE? From these pictures below, can someone provide me guidance on what type of electric service this is? There are only 3 conductors on the pole. All the 3-phase I have seen elsewhere has 4 conductors and 3 transformers
> Thanks in advance!
> John


John, if you are going to be involved in this stuff on a regular basis, you should read up on the differences in Delta and Wye configurations and voltages. I think you got what you needed so, good luck.


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## Southeast Power (Jan 18, 2009)

splatz said:


> You already have your answer, but in short if there's two transformers and three phase power, it's open. If it's 240/120, it's not wye.
> 
> I am curious why the manufacturer voids the warranty for an open wye or open delta service, they probably have a good reason and may have figured this out the hard way.


Just a word of caution, I have spent 40plus years in an area where light industrial and commercial building use an open delta. I have noticed exactly one, yup one, closed delta system.
They are rare but, they are out there.


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## Forge Boyz (Nov 7, 2014)

Southeast Power said:


> Just a word of caution, I have spent 40plus years in an area where light industrial and commercial building use an open delta. I have noticed exactly one, yup one, closed delta system.
> They are rare but, they are out there.


That's interesting, because I can think of at least 3 from customers that we have. It must be a regional thing.

Sent from my SM-G970U using Tapatalk


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## Forge Boyz (Nov 7, 2014)

Forge Boyz said:


> That's interesting, because I can think of at least 3 from customers that we have. It must be a regional thing.
> 
> ETA make that 4. And at least one of them is 480v 3wire ungrounded.
> 
> Sent from my SM-G970U using Tapatalk




Sent from my SM-G970U using Tapatalk


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## paulengr (Oct 8, 2017)

Southeast Power said:


> Just a word of caution, I have spent 40plus years in an area where light industrial and commercial building use an open delta. I have noticed exactly one, yup one, closed delta system.
> They are rare but, they are out there.


Delta delta used to be popular in the 1950s and 1960s because of “continuity”. Many have been converted from ungrounded deltas to either corner grounded or high resistance grounds using a zig zag transformer.

High leg delta is weak if the 3 phase load is significant but utilities sometimes use it because they can make a wired delta with just 3 transformers or if your loads grow to the point where the original 2 transformer open delta doesn’t work just add the third transformer. If a single transformer fails repairs are cheaper than with a 3 coil 3 leg transformer,


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## qisdtech (10 mo ago)

splatz said:


> You already have your answer, but in short if there's two transformers and three phase power, it's open. If it's 240/120, it's not wye.
> 
> I am curious why the manufacturer voids the warranty for an open wye or open delta service, they probably have a good reason and may have figured this out the hard way.


In the high-power broadcast transmitter world, the manufacturers have explained it the reason for not allowing Open Delta as this:

"Although this connection delivers three-phase currents which are approximately symmetrical to a three-phase symmetrical load, the currents flowing in the high voltage circuit are not equal nor are they 120 degrees apart. The maximum safe output of the bank operating in this manner is 58% of a 3 pot Wye/Delta bank. The system is grossly unbalanced, both electrostatically and electromagnetically."

I'm definitely new to this, as this is my first 3-phase site which has only 2 POTs and is Open Delta.


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## paulengr (Oct 8, 2017)

qisdtech said:


> In the high-power broadcast transmitter world, the manufacturers have explained it the reason for not allowing Open Delta as this:
> 
> "Although this connection delivers three-phase currents which are approximately symmetrical to a three-phase symmetrical load, the currents flowing in the high voltage circuit are not equal nor are they 120 degrees apart. The maximum safe output of the bank operating in this manner is 58% of a 3 pot Wye/Delta bank. The system is grossly unbalanced, both electrostatically and electromagnetically."
> 
> I'm definitely new to this, as this is my first 3-phase site which has only 2 POTs and is Open Delta.


SOME of this is true in some ways.

Looking at it from a delta perspective two sides see normal impedance since each sees only one transformer. Hopefully they are both the same %Z. But the third side sees twice the impedance because the two low voltage coils from the transformers are in series.

If the two transformers are physically “large” and regulate well compared to the load so that you don’t ever go below 1-2% voltage drop, you won’t know the difference. This is normally the situation where this is used. Say a commercial building where the only three phase load is a small pump or air conditioner.

Now an idiot thing to do would be measuring the voltage phase angles to ground/neutral. Clearly two are going to be 180 degrees apart and the third is 90. If we measure phase to phase though we still get 120 degrees on voltages. This part is just lying.

Similarly the 58% thing is not just lying but wrong math. In a transformer if you have wired individual single phase transformers or parallel 3 phase transformers you ADD their individual kVAs. As a short cut you can just multiply by three on a closed delta or wye but on an open delta you only have two so we have 67% or 2/3rds of closed delta. It’s still not a good idea to actually try to run at name plate kVA though…

If however you go anywhere near loading up the transformers where a normal 3 phase one will drop say5-10% during a mild temporary overload this setup will do that on the one side while the other two remain fairly stable because there really isn’t a third coil. At this point the VOLTAGES will still be 120 degrees apart but the currents won’t be because one side lags far more than the other two. If the loads are 100% resistive things would stay 120 degrees but reactive loads will cause the vectors to be off because the current draw is uneven.

Practically the effect on motors is that they must be derated. At 1% voltage unbalance it’s negligible but at 5% according to NEMA you derate to 75% of name plate and more than that is not allowed.

In 3 phase bridge rectifiers the effect is that one phase pulls considerably more average current than the others. In a full “single phasing” condition the two strong legs would be 1.732 times the weaker one. At unbalanced voltages you get something in between which can overheat the rectifier. In addition this causes harmonics which in a passive rectifier show up on the DC side. These are pretty common anyways since many sites are wye-wye so I would not automatically assume there isn’t adequate filtering since it’s a common issue (harmonics of 60 Hz).

So it CAN work with no issues. But making assumptions on either side is a bad idea. I work for a motor shop. It makes me look good if I can show a high leg delta is causing motor issues but makes me look stupid if it’s not a real issue and the customer finds out. You just have to be careful with voltage regulation under load. I normally have the advantage of working with existing loads where someone already wired it up though, not gazing into a crystal ball when the equipment manufacturers won’t tell you how their equipment performs and just make performance your issue which is what they are doing. If I never got over 50% loading under all conditions even say starting a sump pump, go for it. But if it’s even close to loading up I’d pass the buck to the customer making it their responsibility to argue with a utility that normally fights to avoid spending money on a transformer. Get a delta-wye while you are at it with 208/120 if you can. This gives everything a 60 degree phase shift cancelljng all odd harmonics and all utility side ground faults and splitting voltage unbalanced on the line side across two phases. It’s just cleaner power. Utilities don’t like them because they regenerate the third phase on the line side and they are slightly more expensive than wye wye.


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## just the cowboy (Sep 4, 2013)

qisdtech said:


> Good morning! I just found your forum via google. I am trying to determine if I have 3-phase WYE electricity at a radio transmitter site where we plan to install a new transmitter. The transmitter requires either 3-phase CLOSED Delta or WYE, 240-volt service to operate properly. The transmitter cannot accept open delta or open wye service without voiding the warranty.
> The Electric provider tells me this site is 3-phase 120/240 WYE service. They did not specify if it was Open WYE or standard WYE. I am under the impression that 3-phase requires 3 transformers, and the site only has 2.
> Is there such a thing is Open WYE? From these pictures below, can someone provide me guidance on what type of electric service this is? There are only 3 conductors on the pole. All the 3-phase I have seen elsewhere has 4 conductors and 3 transformers.
> 
> ...


You do not say what size the new load is. I would go with a delta to wye drive isolation transformer bonded. I have dealt with overseas equipment that would only accept it do to the drives and warranty. I think you have the same thing brewing


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