Two phase to three phase transformation

Thread Starter

ersch

Joined Sep 6, 2014
7
I need to convert a two phase three wire system to a three phase four wire system. I can do this with a Scott T transformer but I am not sure where to connect the neutral on the three phase secondary windings to achieve the four wire output that I need.
 

jpanhalt

Joined Jan 18, 2008
11,087
Welcome to AAC.

1) It would help to know in what country you are.
2) Are you committed to using the Scott T transformer, or will you consider other approaches (e.g., rotary or solid state)?
3) How much power (voltage and current) do you need for the three-phase?
4) Do you need the conversion to run a motor? If so, do you want variable speed too?

John
 

Thread Starter

ersch

Joined Sep 6, 2014
7
1) US
2) Yes. I am committed to use a Scott T transformer.
3) Total power will be 45 kVA with an input of 240 V, two phase, three wire and an output of 208/120 V three phase, four wire.
4) The load is general power and not a motor so no variable frequency is necessary.
ersch
 

tcmtech

Joined Nov 4, 2013
2,867
Where in the USA do you have two phase power and not a full three phase power?

If you are thinking that the common 120/240 VAC that is present in the vast majority of home is two phase you're already wrong. It's simply a single phase 240 VAC supply that has it's center tap connected as the common/ground reference point.
 

Electric Al

Joined Nov 6, 2013
55
I need to convert a two phase three wire system to a three phase four wire system. I can do this with a Scott T transformer but I am not sure where to connect the neutral on the three phase secondary windings to achieve the four wire output that I need.
Are you sure it is 2 phase , and not single phase 120 or 240 ?

You can do it with a roto- phase unit and a step up 3 phase transformer , which will have a neutral connection !




1) US
2) Yes. I am committed to use a Scott T transformer.
3) Total power will be 45 kVA with an input of 240 V, two phase, three wire and an output of 208/120 V three phase, four wire.
4) The load is general power and not a motor so no variable frequency is necessary.
ersch
 

Thread Starter

ersch

Joined Sep 6, 2014
7
Where in the USA do you have two phase power and not a full three phase power?

If you are thinking that the common 120/240 VAC that is present in the vast majority of home is two phase you're already wrong. It's simply a single phase 240 VAC supply that has it's center tap connected as the common/ground reference point.
 

Thread Starter

ersch

Joined Sep 6, 2014
7
I appreciate your help but it is counterproductive to assume that I don't know the difference between a single phase common three wire system and a two phase (displaced 90 degrees) input connected in an L fashion with the corner as the neutral. Please try to help me by answering the original question as stated.
 

jpanhalt

Joined Jan 18, 2008
11,087
In the USA, two phase with just a common (white wire) is no longer code. Two phase/single phase 220/240V with green (safety ground) is code and two-phase with green and a white (four wires) -- from which you can get two, single phase circuits -- is also code. At least, that is as I remember it. My NEC book is in another city, so I cannot check it now. Basically, you are not allowed to use the grounded wire (i.e., the white/com) as a ground. If the third wire is white, then you don't have a safety ground.

Are the wire colors non-white or non-green X 2 (e.g., a black and a red) with a white or a green wire . Is the third wire white or green? If the third wire is green, that can only be used as the safety ground, not as a common. Is this wiring in metal conduit or plastic?

John

Edit: Sorry, I was writing while post #7 was made and didn't see it. Good luck. I would and do use a rotary converter.
 

BR-549

Joined Sep 22, 2013
4,928
Thank you ersch. I had never heard of a Scott T transformer. Very interesting. I wasn't aware of early 2 phase history.
Do you have a print of the scott t? I want to compare it to the one I reviewed.
 

Brownout

Joined Jan 10, 2012
2,390
I am interested in your complete reply. All I got is "Here we go..."
That's all you're gonna get. You're experiencing Pennsylvania (USA) humor.

From the little bit of reading I did, a Scott T transformer converts between 4 wire two phase and 3-wire 3 phase. But you said you wanted to go from 3-wire two phase to 4-wire 3 phase. Maybe more details would help us to help you for figure it out. Seems there are no Scott T transformer experts in here.
 
Last edited:

GopherT

Joined Nov 23, 2012
8,009
I appreciate your help but it is counterproductive to assume that I don't know the difference between a single phase common three wire system and a two phase (displaced 90 degrees) input connected in an L fashion with the corner as the neutral. Please try to help me by answering the original question as stated.
Are you operating an antique generator of some sort? Or are you running 3-phase into a Scott T transformer to get the 2-phase power.
No US utility is running 90-degree generators any more. Without a 90-degree generator, or 3-phase into a Scott T, you have no 2-phase power source (90-degrees out of phase).

Until we have an answer, it doesn't sound like anyone around here is motivated to give you an answer.
 

GopherT

Joined Nov 23, 2012
8,009
I read Philly does.
I stand corrected.

Only city center area of Philadelphia is running 90-degree 2-phase power. Unless you live there, or you are running an antique 90-degree generator, or you are running 3-phase into a Scott T, you have no 2-phase power source (90-degrees out of phase).

Until we have an answer, it doesn't sound like anyone around here is motivated to give you an answer.
 

BR-549

Joined Sep 22, 2013
4,928
Oh I am motivated, but I don't have the knowledge. That's quite a circuit. From what I can find, I think Brownout is right though.
I think Philly uses these to supply 2 phase to their customers.
 

Lestraveled

Joined May 19, 2014
1,946
ersch
You have to expect a little skepticism? This is your first post on this forum. You pose a question based on a highly unusual power form as if everyone has it available in their backyard. You present no schematics, no wave forms. You have asked a complex question involving a very unusual waveform. We are not mind readers, and you appear resistant to provide information needed for a meaningful exchange.
 
Last edited:

Thread Starter

ersch

Joined Sep 6, 2014
7
ersch
You have to expect a little skepticism? This is your first post on this forum. You pose a question based on a highly unusual power form as if everyone has it available in their backyard. You present no schematics, no wave forms. You have asked a complex question involving a very unusual waveform. We are not mind readers, and you appear resistant to provide information needed for a meaningful exchange.
Not a very friendly answer. If everybody had it in their backyard I probably would not have to pose the question. No schematics are required. Waveforms are not unusual: The two phase input has a garden variety sine wave each displaced by 90 degrees and the output likewise has garden variety sine wave each of three displaced by 120 degrees. I do not require mind readers: a simple knowledgeable person will do. I can do the transformer conversion but I was asking how to establish a neutral connection in the output. When I get my answer, and I will, I will forward it to you so you can help someone else.
 

BR-549

Joined Sep 22, 2013
4,928
From what I see, it looks like a delta out...so I don't think your gonna get a neutral.

And you guys thought I was bad.
 
Top