# figuring single phase loads on 3 phase transformer

Discussion in 'General Electronics Chat' started by stevegarren, Dec 10, 2008.

1. ### stevegarren Thread Starter New Member

Dec 10, 2008
2
0
I need to configure a 3 phase transformer as a power source for a construction crew. I read the section about 3 phase power systems and it probably told me how to do this but it isn't hard to get over my head when it comes to 3 phase transformers.

What I want to know is basically this, say I have an available 480 vac 50 amp 3 phase circuit available to me. I want a transformer to step this down to 208/120 vac. To fully utilize the 480v 50a circuit I would want a 24 KVA transformer correct? How would I determine the maximum single phase loads on this transformer?

2. ### stevegarren Thread Starter New Member

Dec 10, 2008
2
0
I guess it would be a 48 kva transformer I would need.

3. ### floomdoggle Senior Member

Sep 1, 2008
217
2
You need to show the input wiring. And ask your electric company what they can supply you with. Anything over 220v is not user friendly. A center tapped input is easily stepped down by using one hot side and the neutral. Unles you are well versed in electrical wiring, using a transformer, unless required by the output, is not preferred. Whatever unit you are using should be, or have, an adapter from the manufacturer.
Dan

4. ### Pich Senior Member

Mar 11, 2008
119
5
First of all you need to determine if the crew needs 3 phase if not thinks would be much more simple. then you just need to rate the tranformer to the load required and to a standard distribution panel. If you are stepping down to 208/120 this would mean a 3 phase tranformer. The question is what standard size of tranformers is available that will meet the amperage and voltage. tranformers are rated in KVA and volts you will need to derive the amperage by knowing if it is a star or delta primary, in other words if a maximum 50 amps is desired on a Y connection then the KVA per tranformer would be 480 X .578 = 277volts X 50 amps =13.8KVA of course it would be 115 amps at 120 volts

My rant
I would hope you know all the electrical code rules on this job, hopefully this installation is not on a outdoor contruction site were proper grounding is paramount.