1. New Guest
Join Date
Dec 2010
Posts
4
Post Likes

## Question about a stepdown transformer

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.

2. Professional Member
Join Date
Jul 2000
Location
Dallas,Texas
Posts
5,134
Post Likes
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
Last edited by wolfdog; 02-10-2011 at 08:36 PM.

3. Regular Guest
Join Date
May 2010
Posts
1,296
Post Likes
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

4. New Guest
Join Date
Dec 2010
Posts
4
Post Likes
Thanks for the help

5. Professional Member
Join Date
Aug 2000
Location
Austell, Ga.
Posts
1,307
Post Likes
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.

6. Regular Guest
Join Date
May 2010
Posts
1,296
Post Likes
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

7. Professional Member
Join Date
Jul 2000
Location
Dallas,Texas
Posts
5,134
Post Likes
I'm open to negotiation RichardL.

8. Originally Posted by RichardL
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.

9. Professional Member
Join Date
Jul 2000
Location
Dallas,Texas
Posts
5,134
Post Likes
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?

10. Professional Member*
Join Date
Jun 2010
Location
Posts
2,209
Post Likes

## Richardl both choices less than optimal

If I could only get da' Wolfdog seeing straight on the 9mm/45 issue all would be well.
40 cal better ballistics and knockdown!

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•

## Related Forums

The place where Electrical professionals meet.