Transformer Questions

[A/A Fuel GTX]

I am having difficulty in figuring the following two questions. I am studying for my exam and can't seem to find the calcs I need for these questions.

1. What is the primary line current for a fully loaded 45kva, 480v to 120/240 3 phase transformer?

2. What is the secondary line current for a fully loaded 45kva, 480v to 240v 3 phase transformer?

Any input would be greatly appreciated.

 

[TAZMAN]

The following is based on this being a delta system. To find the line current you take 45,000 / (480) * 1.732 (831) = 54 amps. To find the phase current if this is a balanced system with 3 single phase 15 kva transformers. You take 15,000 / the phase voltage 480 = 31.25 amps. The phase current times 1.732 gives you the line current. The line current divided by 1.732gives you the phase current.

 

[A/A Fuel GTX]

Ok, I understand primary line current and for the secondary line current, I would take 45000/415 (240*1.732) which equals 108a....correct?

 

[TAZMAN]

correct

 

[A/A Fuel GTX]

Great, Thank you....now one more little problem I'm having is related to True and Apparent power calculations, does a power factor of say 85% play into the equation of figuring true and apparent power?

 

[charlie b]

(Apparent Power) times (Power Factor) equals (True Power).

 

[A/A Fuel GTX]

So the true power of a 20a, 120v, 85% power factor circuit would be 2040w?

 

[charlie b]

Dat's so.

 

[A/A Fuel GTX]

Thanks, Charlie