single phase transformer?

[FirstRate001]

Hello every one I have a problem I am designing a Power distribution panel...And I have the size of the transfoermer wich i did the calculation for a three phase 25 kv @ 3 phase 480 to a 240/120v.

I know that for the primary fuse I will be using 38 amps and for the secondary is a 75 amps. however i would like to know if these numbers would be good for a single phase transformer?

thanks all in advance.

 

[waross]

25000/240=104.2 amps
Your fuses are a little small.
respectfully

 

[FirstRate001]

thank you for your reply and your advice but doesn't the formula for is p/I x E (dealing with 3 phase application use square root of 3= 1.732) I am just trying to get this right...

25000/(240*1.732)=60.14

60.14*1.25=75.17 amps


Please let me know if this is correct, I will be greatly appreciate.

 

[resqcapt19]

Unless you are installing a 3 phase wild leg delta transformer, 120/240 is a single phase voltage and you do not use the square root of 3 in the calculations.
Don

 

[dpc]

Your question was about a single-phase transformer, not a three-phase transformer.

 

[l3city]

I recommend:
Primary: 70A/2P
Secondary:125A/2P
This is just an approach but you are encouraged to do your own calculations and conclusions according to the situation (voltage drop for example)
Regards

 

[FirstRate001]

thank you all.

 

[rbulsara]

Thanks for what?

What is your transfromer? single phase or 3 phase?
25kva??

Where does 38A primary fuse comes from? That tells me that you have a 3 phase unit.

a 480V, 3 ph, 25kva tranfromer will have 30A primary amps.
a 240V, 3ph secondary will have 60A. This unit can still have 120V if one of its phases is center tapped. If this is the case your fuse sizes in your original post are correct.

A 480V to 240/120 single phase unit will have 52A primary and 104A secondary.

What is that you have?