Single Phase to 3 Phase Conversion

[nightfox1925]

Hi folks, I came across a question of having two single phase transformers used to develop a three phase output. I thought they are going to use 2 - 2-winding transformers and connect them in Vee-vee arrangement. It came out that they are planning to use two 230VAC single phase VARIACs. I am aware that these single phase VARIAcs are actually auto-transformers (with input + common). They are planning to connect the "output common" of VARIAC 1 to the line output of VARIAC 2 (like a Vee-vee connection). I think this will not work out since it would develop unacceptable voltage unbalance which would draw high current on one of the phases and it might fry up the VARIACs as well.

Given the situation, is there any possible connections that I am not aware of?

 

[DanDel]

How can you get 3-phase out of two 1-phase transformers connected to the same source, no matter what the configuration?

 

[nightfox1925]

You're right dandel, you should have at least a three phase source!!!

 

[dpc]

If the source is single-phase, you'll need something more than a couple of transformers.

If it is for a small motor, a VFD can be used. Or a small M-G set.

 

[peebee]

It might be possible.... try a search on "static phase converter" -- here's one site that popped up:

http://homemetalshopclub.org/projects/phconv/phconv.html

Usually these things rely on a capacitor to derive the out-of-phase third leg, and usually the capacitor needs to drive an inductive load (a motor). Usually the driven motor must be significantly derataed.

"Unacceptable voltage imbalance" is subjective. How bad can it be but still be good enough?

"Might fry up the VARIACS": depends on the rating of the VARIACs.

We'd need some more detail on your circuit to be more specific in the response.

 

[nightfox1925]

Thanks folks for the caution. I looked again at the diagram they submitted and they have attempted to persuade me that they can do it by interconnecting the output commons. However, if they do this, they will end up having say Vs on the two output line and 2*Vs on one line (voltage between the two output leads)...basically resulting into a critical voltage unbalance and may exceed load rated voltage and Variac rated voltage.

 

[jraef]

There is a "transformer method" of conversion, but the guy who developed it will not share details on it without paying him, because he does not sell the transformers, only the design specs. But I have heard from people who have done it and they say that although it works, it is VERY load dependent, so if the load changes, the system goes unbalanced.

http://unique3phase.com/

 

[itsmoked]

Yeah, for the price of the movies, and the $108 for wire, $30 for capacitors, $$ for etc.. You could probably have just gotten a VFD.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[dpc]

http://www.ronkelectrical.com/add_a_phase.html