Three Phase Transformer on single phase?

[MikeMl]

I have a h.v. plate transformer with a three-phase delta primary rated at 240V 60Hz 4kW. It came out of an industrial RF heater.

How much can I get out of it if I run it on 240V single phase. Leave the third wire primary wire unconnected? Is there a better way to use it on single phase? Dont want to screw with a rotary or solid-state one-to-three phase converter.

 

[MaxHeadRoom78]

Keep in mind that a 3ph transformer is essentially three 1ph transformers just mounted on the same frame, each with their own primaries and secondaries.
Feed two delta conductors of a 3ph with 1ph will energize one core and the secondary result should be what ever the ratio is on that core.
Max.

 

[tcmtech]

Most three phase transformers will not handle having the primaries of all three phases wired together for single phase but they will take having the primaries of the outer two windings wired together (in phase) with the third center primary winding left floating (core goes into saturation with all three powered up) and all three secondaries wired together in parallel (outer two in phase with each other center 180 off from them ) which will give you a good 2/3 ~3/4 of the three phase rated KVA capacity continuous duty.

 

[Grossel]

tcmtech is correct, the transformers core is likely to saturate when just connecting all phases together.

Also (also just sait - I just rephrase), cooling capabbilities (aka wattage) of an transformer will be reduced when only one phase is generating heat. How much depends on how the transformer is assembled - what method to get rid of heat.

 

[MaxHeadRoom78]

THe op mentions using two conductors only which would mean one core, essentially 1ph.
Nothing mentioned about all three.
Max.

 

[MikeMl]

More info:

The core appears to have two windows with three vertical bars. There are three primary windings, one each on the vertical bars. There are also three secondary windings, one each on the vertical bars.

The windings are separable, so can be rewired any way that makes sense.

The picture shows the big tranny, input on left, output on right.

 

[MaxHeadRoom78]

That is the three '1ph' transformers referred to.
A 2 wire 1ph supply would power up one core only.
Are you looking at it for a single phase transformer usage?
Max.

 

[MikeMl]

If I wire up only one primary winding, (no current in the other two), it seems like the max I could get out of it would be one-third of the rated three-phase power?

How about if I parallel the two outside primaries (leaving the middle one unconnected) such that there is no flux in the center bar. Can I get two-thirds of the rated power that way?

I realize that the filtering on the HV secondary will have to be increased because the rectifiers are getting only two pulses per cycle instead of six.

 

[tcmtech]

Looks like a standard three phase transformer.

As said earlier wire the primaries on the two outermost coil sets paralell with each other and leave the middle one disconnected.

The three secondaries can be wired in any combination you need to get whatever voltage you need.

 

[dr pepper]

Wiring all 3 togther will saturate the core.
If you want to do something 'quick' then the trans will only give 1/3 of its original rating by just using one coil, and that is assuming you have access to the star point for the neutral (and the trans was wound star not delta).
You could get most of its power rating by adding 2 caps, to generate the 3 phases, mains in one, then a cap for a phase shift to the second coil and another for the third, this is assuming the trans was originaly wound star, however you'd need some pretty bg caps.
Another way you can do it, and I've seen this done is use a single to 3 phase motor variable speed drive to give you the 3 phases, the trans would probably be more efficient at 100hz, however this works out expensive, and a vfd gives you 3 x 220v not 3 x 415v, you can get round this by connecting the dc bus - of the vfd to the star on the trans, assuming again its wired star.