Connecting three single phase transformers to get single 3 phase transformer

-------------------------

** Your Q is totally absurd.

In order to use a 3-phase transformer, one must first have a 3-phase supply available.

..... Phil

Wire each incoming phase to a transformer and connect the other terminal together in a single point to create an artificial neutral

Do the same on the output side

I guess you are doing this to get an isolated 3 phase transformer?

Cheers

Klaus

Inputs and outputs are wired the same way, either both Y or both delta. What extra wires you're referring to is anyone's guess.

NT

Think of "delta" as a "ring" and you have answered the question yourself.

Of course, you need to check the maximum primary voltage to see if you can connect the primaries in wye (star) or delta depending of the input voltages available.

If the secondary is center tapped and you connect those together into a wye configuration, the opposite end of each secondary is useless.

Think about what outputs are required. Are you feeding an AC system or a rectifier and what voltages do you trying to generate ?

FWIW, you technically only need two transformers. This is called open delta. The regulation and balance isn't as good, though.

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:

Your answer/response is equally absurd. It is possible to connect 3 single phase transformers in delta or wye configuration to get 3 phase output. I have not tried it out before, but now will, using the hints/suggestions from the others who have responded to my query.

It not be totally isolated, because the center taps of each of the three secondary windings can be connected to e.g., the chassis ground. Am I right ? I have never tried this out, but will do so soon.

Phil is right. You can't get a three phase output from a single phase supply using only transformers. Elementary vector math should make this plenty clear.

Jeroen Belleman

If you do not have at least a 2-phase mains supply, forget it. (2-phase does not imply center-tapped 220V).

a Scott-T connection.

But if you want 3-phase from a single phase input (like 240VAC =

120:120 in North American residences) you either need a VFD type 3-phase inverter, something mechanical like a rotary phase converter, or a phase shifting static phase converter.

For higher power (as in running a Bridgeport mill in your garage) I suggest a rotary phase converter, which uses a 3-phase motor (generally of higher HP than your target motor) idling away with nothing connected to the shaft. There are various techniques of starting it, from a rope to more automatic methods. The motor can typically be had for next to nothing. A VFD is another option and has the advantage of allowing you to vary the frequency, however high power ones generally either require 3-phase input or are heavily derated with single phase input (this is a design decision - how much filter capacitance to add to the input).

Static phase converters use a bunch of capacitors and don't do as good a job generally, and are only balanced under one set of conditions.

--sp

--
Best regards,  
Spehro Pefhany

To get some meaningful answers, you need to specify at least the following points:

What is the available input power ?

• Single phase (e.g. 230 Vac)

• three phase delta connected (400 Vac)

• three phase wye/delta e.g 230/400 V ac

What are the transformer nominal ratings

• Nominal primary voltage

• Nominal secondary voltage (end to end ignoring any central taps)

What should the output be

• Three wire delta

• four wire wye/delta with neutral

• some rectified DC

Specify these parameters and you might get some usable suggestions.

If the input is single phase, you can get something that resembles three phase with three additional capacitors, but the power handling is reduced to a small fraction. Such tricks has sometimes used for driving a three phase motor from a single phase, but the output power is minuscule.

It is

No. You'd get 3 outputs, but no different phases.

It is possible to convert 2-phase with a 90 degree phase shift to 3-phase with a Scott T transformer setup (actually 2 transformers wired together.) And, you could convert single phase power to 2-phase with a 90 degree phase shift network. I tried to design one of these a long time ago, and it took me WAYY too long to realize that it can only work with gigantic inductors and capacitors, and the imaginary power draw from the mains would get the electric company coming after me with pitchforks.

Any 3-phase motor can be set up to create a 3rd phase leg from single phase power, but it is a bit tricky to get these to work well. Again, the power company won't be real happy with it.

Jon

-----------------------------

** No it isn't.

Only a raving nut case would think otherwise.

Which describes you precisely.

..... Phil

You can run a 3 ph motor on single phase power. The ROT is you can get about 2/3 the name plate power. So with a 10 hp three phase motor you can get about 7 hp out.

Try searching over in Rec.Crafts.metalworking for details.

Dan

Why 3 on the secondary? are these transformers actual or hypothetical?

--
This email has not been checked by half-arsed antivirus software

expect smoke,

--
This email has not been checked by half-arsed antivirus software

Split phase?

Probably center tapped is my guess.