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phandley
02-10-2011, 05:56 PM
Hello,
I am looking to find the rated amps for the sencondary of a stepdown transformer. Three phase primary is 460/575V, secondary 230V, 200VA. I am not sure if I should calculate the secondary side of the transformer as 3 phase or single since it is only 2 wires coming out of the secondary.
Calculations:
3 phase- 200/230/1.73= .5 Amps
Single Phase- 200/230= .87 Amps

I am not sure which is correct and I could really use the help thanks.

wolfdog
02-10-2011, 07:19 PM
There are no three phase transformers, just multple transformers placed together in a package.
In this case you have 1 transformer fed from 3 phase. However it is only tied to 2 of the 3 phases.
2 wires in 2 wires out, figure it as single phase.

IF this was a three phase transformer your calculation is incorect.

You have to allow for the 3 phases of power.

The equation is I = (KVA x 1000)/ (1.73 x E)

Assume this is a 20KVA 3 phase transformer instead of 200VA single phase.

(20 x 1000) / (1.73 x 230)

20000 / 397.9 = 50.26 amps

ZeroTolerance
02-10-2011, 07:26 PM
If it only has two wires coming out of the secondary it is single phase. I am not sure I understand you by saying, "There are no three phase transformers" when in fact there are? They are in delta or wye configurations

phandley
02-10-2011, 07:47 PM
Thanks for the help

RichardL
02-10-2011, 08:16 PM
The "Only" thing Wolfdog has been in error about is his chosing a puny 9mm against a full house 45ACP. His statement that there is no such thing as a 3ph. transformer is correct. Just because a 3ph transformer looks good on a schematic diagram, in all actuality it is nothing more than single phase transformers connected in Delta-Delta, Wye-Delta or Delta-Wye configuration.
Now....If I could only get da' Wolfdog seeing straight on the 9mm/45 issue all would be well.

ZeroTolerance
02-10-2011, 08:35 PM
I'd rather have a 9mm over a 45 as well, for many reasons. That is why I carry a 9mm and not a 45acp

wolfdog
02-10-2011, 10:21 PM
I'm open to negotiation RichardL.

jayguy
02-10-2011, 10:34 PM
The "Only" thing Wolfdog has been in error about is his chosing a puny 9mm against a full house 45ACP. His statement that there is no such thing as a 3ph. transformer is correct. Just because a 3ph transformer looks good on a schematic diagram, in all actuality it is nothing more than single phase transformers connected in Delta-Delta, Wye-Delta or Delta-Wye configuration.
Now....If I could only get da' Wolfdog seeing straight on the 9mm/45 issue all would be well.

don't forget wye-wye...but who would use those? stupid triplens!

as for the transformer...i do not believe that he has a 3 phase transformer PRIMARY and a single phase SECONDARY. my guess is that his transformer is a multi-tap PRIMARY transformer.

approximately 0.87 amps would be correct for 230 VAC, single phase.

wolfdog
02-10-2011, 11:44 PM
I don't believe I have ever met a Wye/Wye transformer configuration.
Delta/Delta for isolation and/or step down.
Delta/wye to produce a neutral and/or step down.
Wye/delta to step up.

The obvious question is Wye?

genduct
02-12-2011, 05:24 PM
If I could only get da' Wolfdog seeing straight on the 9mm/45 issue all would be well.
40 cal better ballistics and knockdown!