

I found a 5 KVA transformer. It looks to have never been used. The guy I got it from said it needs to be wired backward. (What ever that means) It's a GE catalog number 9T21B1004. It has two sets of 4 wires. They are marked, H1, H2, H3, & H4 all small wires. X1, X2, X3, & X4 all larger wires. It shows a winding of the Hs and Xs. On top are the Hs, they are H1 H3 H2 H4 Under that the X winding. X4 X2 X3 X1. (Primary line on H1H4.) (Volts 240, connect H1H3, H2H4.) (Volts 480 connect H2H3.) (Secondary line on X1X4.) (120 volts X1X3, X2X4.) (240 volts X2X3) (type CMS) (40 C AMB) (Class 180) I am wanting 3 phase 480 volt out, with 240 volts 3 phase (using 20 hp motor and phase converter)in. Could someone please help me with wiring this transformer up? thanks,

In NEMA nomenclature, H represents the high voltage side, and X the low voltage side.
As you have observed, the wire size on the low voltage side is larger (lower AWG number).
Most transformers are wound as Y. Rarely are these wound as ∆.
So, for 240 in and 480 out, you would connect A(240), B(240), and C(240) to X1, X2, and X3, respectively, and insulate X4; and you would connect your 480 load to H1, H2, and H3, for A(480), B(480), and C(480), respectively, and insulate H4.

Careful!
I show that number in the GE Buylog as being a 1 phase transformer!

Listen to Jraef. The data you supplied is for
a singlephase transformer.
<als>

Thanks to you all for your information. I'll set this box aside and go back to looking for a true 3 phase transformer. By the way, how can I tell on the sticker that it is 3 phase?

One other concern; is that the size transformer you need? What is the load you are going to put on this transformer? I see that you have a 20 hp converter. Hopefully you are not trying to run a 20 hp load on a 5 kva transformer.
An alternative to finding a three phase transformer is to find two more single phase transformers. A three phase transfomer is nothing more than three transformers in one package. However, this does leave more external wiring for you to do which already appears to be a concern.

All but two of my machines are 240 3 phase so I didn't figure I needed a 480 transformer for them. I will have to take all the power from the same 3 phase motor, for both the 240 volt motors and the 480 volt motors . You are so right, I know very little about transformers. My hopes are that someone with the know how, will be willing to help me with the wiring.

Are your 480v motors multispeed, singlevoltage, or rare frame sizes?
I would just look to get "9wire" or "dual voltage" motors that run on 240/480v if the frame sizes are common.
Usually any AC control circuitry is fed by a small control transformer off a single phase from the main power supply so that transformer can be retapped or replaced.

Matt, The surface grinder has a 480 3 phase motor that has to use that type of motor. It would need rewired if I want it to be 240 3 phase. The lathe has a 480 control transformer. I could change the lathe control to 240 volts but I still would need a 480 transformer for the grinder.

Call up Acme Transformer and ask for a three phase dry type that is twice the KVA of the motor HP you want to run. I.E. if grinder happened to be 1 1/2 HP a 3KVA would be the right size. I have run 1 1/2 HP four speed 440v motor for a good number of years on an Acme 3 phase 3KVA bought new for $230. A little more now I suppose [img]smile.gif[/img]
John
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