Installing a 3 Phase Transformer on Single Phase.

[Sparks4All]

We have a customer that wants us to use a 3 phase transformer on a single phase system. It is a single phase 480/277 with a 120/208 output. Will this work properly? My concern is the derived neutral.

 

[LarryFine]

No, it will not provide 120/240v. Nor will it provide 120/208v.

 

[Besoeker3]

We have a customer that wants us to use a 3 phase transformer on a single phase system. It is a single phase 480/277 with a 120/208 output. Will this work properly? My concern is the derived neutral.

Both 480/277 and 120/208 are three phase voltages.

 

[kwired]

No, it will not provide 120/240v. Nor will it provide 120/208v.

It not necessarily totally useless, but definitely will not have full rated kVA ability. What can or can not work will depend on design of the transformer - Delta -wye, wye-wye, delta-delta, single core, multiple cores...

 

[drcampbell]

Um, "work properly" for what?

If you have single-phase 480 available, you could use it to supply single-phase 120.
If you have single-phase 480 available and it has three independent cores, you could use it to supply single-phase 120/240.
If you were to back-feed it with 120, you could use it to supply single-phase 480.
But each of these ideas falls somewhere between "inefficient use of materials & energy" and "wacky".

What, exactly, are you trying to achieve and why are you contemplating installing the wrong transformer?

 

[jaggedben]

We have a customer that wants us to use a 3 phase transformer on a single phase system. It is a single phase 480/277 with a 120/208 output. Will this work properly? My concern is the derived neutral.

It is possible to derive three phases from two hots and a neutral that belong to a wye system. A special transformer is required, you cannot use a normal three-phase to three-phase transformer. There is no other sense in which you can get three phases from a single phase with a transformer. A phase converter might be another option.

It's not very clear what 'it' is in your original post.

 

[Sparks4All]

We only need single phase output. The contractor has a 3 phase temporary power sled and he was wanting to tie into an existing single phase 480V circuit for a temporary job shack using the transformer on the sled. this circuit is 1300' from the main project.

 

[Jraef]

So you are asking whether you can use a 480-208Y120V 3 phase transformer, fed with 3 phase 480Y277V input from a generator, to feed a single phase panel with 120/208V using 2 hots and a neutral? If that's the case then yes, but the balance on the 3 phase side will be bad. Does that matter on a generated system? Probably not.

 

[kwired]

We only need single phase output. The contractor has a 3 phase temporary power sled and he was wanting to tie into an existing single phase 480V circuit for a temporary job shack using the transformer on the sled. this circuit is 1300' from the main project.

So you are asking whether you can use a 480-208Y120V 3 phase transformer, fed with 3 phase 480Y277V input from a generator, to feed a single phase panel with 120/208V using 2 hots and a neutral? If that's the case then yes, but the balance on the 3 phase side will be bad. Does that matter on a generated system? Probably not.

Me thinks he has power at the site but only has a 480 volt single phase circuit that he is interested in connecting to, and wants to tie into the transformer on the sled (and not use the generator, presuming there is also one on the sled).

If so I think he can get 120 volts off one secondary phase, will only be 1/3 total kVA rating of the unit available for the most part.

 

[Jraef]

Me thinks he has power at the site but only has a 480 volt single phase circuit that he is interested in connecting to, and wants to tie into the transformer on the sled (and not use the generator, presuming there is also one on the sled).

If so I think he can get 120 volts off one secondary phase, will only be 1/3 total kVA rating of the unit available for the most part.

480V single phase without coming from a 3 phase transformer somewhere?

OK, probably another of those things that you experience in your area that I never see in here, especially when it comes to farm services. I spent a lot of time working in farm country in the pacific Northwest though and I never came across 480V single phase services. But you've taught me that there are things out there that I never experience. Such is the value of a forum like this; lots of different perspectives.

 

[kwired]

480V single phase without coming from a 3 phase transformer somewhere?

OK, probably another of those things that you experience in your area that I never see in here, especially when it comes to farm services. I spent a lot of time working in farm country in the pacific Northwest though and I never came across 480V single phase services. But you've taught me that there are things out there that I never experience. Such is the value of a forum like this; lots of different perspectives.

Well it could be from a 480 or 480/240 single phase source, but I think he means the source is 1300 feet away and he is tying onto an existing 480 volt single phase circuit. What may normally operate from said circuit may be fairly limited. 480 volt lighting maybe? Single phase supply with step down at the load end is possible, but if that is what he had existing he really doesn't need a transformer, unless looking for more capacity than existing - but beware you only get 1/3 max of the total kVA rating if it is a three phase transformer.

 

[Sparks4All]

We have 2 legs of the 480v system. It feeds through a ground vault further on to a future gate transformer and 240v panel. He wants to set the job trailer next to the vault and use the temp service sled to feed his 240v trailer. The transformer is a 30KVA transformer with 3 coils with taps.

 

[kwired]

We have 2 legs of the 480v system. It feeds through a ground vault further on to a future gate transformer and 240v panel. He wants to set the job trailer next to the vault and use the temp service sled to feed his 240v trailer. The transformer is a 30KVA transformer with 3 coils with taps.

You will only get 10 kVA @120 volts out of it. You will only energize one primary coil, it will only magnetically couple to one secondary coil.

 

[Jraef]

We have 2 legs of the 480v system. It feeds through a ground vault further on to a future gate transformer and 240v panel. He wants to set the job trailer next to the vault and use the temp service sled to feed his 240v trailer. The transformer is a 30KVA transformer with 3 coils with taps.

OK, one main issue and two other possible problematic scenarios then, depending on the EXACT nature of your transformer. Your initial information is not really clear. So first please clarify:

It is a single phase 480/277 with a 120/208 output

As Larry Fine pointed out first, these are not typical SINGLE PHASE voltage ratings, it would have needed to be a custom transformer for this to be true. So is the transformer a 3 phase transformer or a single phase transformer? Either way, what EXACTLY does the nameplate of the transformer say? All of the words, no guesses. Everything else we tell you will need to be predicated on your answers, otherwise we are playing 20 questions with you.

 

[gar]

190418-1451 EDT

What is a three phase transformer? Typically it is a single EI core, meaning what may be described as a common core. Each of the crossing legs of the magnetic core have a primary and secondary for one phase. There are other ways to make a true 3 phase transformer.

Three separate single phase transformers connected to transfer 3 phase power are not a real 3 phase transformer, but are often referred to as a 3 phase transformer.

If it is a real three phase transformer, then one needs to look at how the windings are wired to determine what can be done.

If it is three single phase transformers, then again how it is wired and what are the winding voltages will determine what can be done.

.

 

[jim dungar]

It appears what from the last OP post, that they have a single phase (2-wires) circuit taken from a 480Y/277V source and they want to have a single phase (3-wire) output. This is a normal industry practice, by using a standard 480:120/240V single phase transformer.

The only issue is that it will not appear as a balanced load to the 3-phase source. But again, this is done every day across the world.

 

[gar]

190419-0913 EDT

There is not enough information about this three phase transformer.

Suppose that it is a true three phase transformer, and has 480 V primary coils, and that all wiring to the primary and secondary coils can be separated. It appears that the secondary coils are 120 V.

With the above assumption connect, phase, two primary coils in parallel such as to not fight each other, and connect to 480 V. Then take the secondaries, each is 120 V, and connect in series so as to add. Now you have a 240 V center tapped secondary. VA capability of the transformer is probably slightly greater than 2/3 of the original VA because total heat generated is less. But the difference won't be much.

.

 

[Besoeker3]

We only need single phase output. The contractor has a 3 phase temporary power sled and he was wanting to tie into an existing single phase 480V circuit for a temporary job shack using the transformer on the sled. this circuit is 1300' from the main project.

What kVA capacity does the shack require?