3 phase transformer on single phase?

[jevs]

My machine has a 220 3 phase transformer, that outputs 3 sets of 120VAC 3 phase. So, basically it supplies 120V 3 phase to each of 3 drivers. I am retrofitting the machine with all new electronics. I am using Rutex drivers. I am also making the whole machine run on 220V single phase. I am wondering if there is a way to hook 220V single phase into this transformer and use it for my power supply to the drivers. This would save me some money, plus it is already mounted and sized for the machine. I ultimatly want to make 100 VDC, but it could be higher.

[murphy625]

Ok. Maybe I am missing something.
Why would you want to use a transformer to supply normal single phase current at normal supply voltages?

Most transfomers are used for Step-Up, Step-Down, or isolation purposes. Is your xfomer a Delta or Y ?(it makes a big difference) What is your mains supply voltage? What was the original purpose of the transformer? Sometimes, buildings that are powered by 480v 3phase industrial power will use 2 of the phases to step down to 220v single phase. For every circuit breaker box for office use, there would be a step down xformer above it. (the neutral of the 2 transfomer taps gets tied to ground)

Anyhow, It should work just fine if you grab 2 of the 115v lines. (but you better double check)
The one I worked on was wired to put out 115-208-115 or something like that. We always used the 2 lines at 115v to feed the front office. (I think this is called a Delta configuration but I might be mistaken)

Hope this info helps
Murphy

[jevs]

I am not sure what you mean in that first statement "Why would you want to use a transformer to supply normal single phase current at normal supply voltages?" I want to take 220V single phase and make a 100VDC (or as close as I can get using this transformer if it is possible) power supply for my drivers. My machine originally ran on 3 phase so it has a 220 V 3 phase transformer that steps down to 120 VAC 3 phase (3 sets of this, one for each driver). What I need to know is if there is a way to reuse this 3 phase transformer on single phase input to make my new power supply. From my schematics it appears that when wired for the normal 220V 3 phase input that it uses two star windings parralleled on the primary side. It then has 3 secondaries which are delta wound. My schematics show 6 different configurations that you can connect the primary side up for different 3 phase voltage inputs. All the primary configurations are star wound, it just changes the connections and makes it look like two star windings paralleled or makes them into one star winding with two windings in each of the 2 leg. Hope this makes sense.

[HillBilly]

With the star primary you will want to rectify the two associated secondaries then send this DC to a shared filter capacitor (The third primary in this situation is dead.). If you had a delta primary you would rectify all three secondaries and send to a shared filter cacacitor (In this situation one primary winding has full voltage and the other two are at half voltage.). In both cases the KVA of the tranfomer will have to be derated 1/3 of it actual value.

Darek

[jevs]

If I have to derate it to 1/3 then that pretty much tells me I can't use it . It would be too wimpy at that point.

Thanks.