Transformer Primary Fault Current

[kchenoweth]

The question states:

1000kVA 34.5kV to 480V secondary transformer 5% imp. Apply 480V to primary side and ground secondary. What is primary fault current?

My calculations come up to 8.0655A, but it says the correct answer is 4.65A. Am I doing something wrong?

[chuyacano]

The question states:

1000kVA 34.5kV to 480V secondary transformer 5% imp. Apply 480V to primary side and ground secondary. What is primary fault current?

My calculations come up to 8.0655A, but it says the correct answer is 4.65A. Am I doing something wrong?


Looks like a missing square root of 3

[dharmikpandya0]

wpuld you like to share the calculation?

[STXERS17]

wpuld you like to share the calculation?

This is what I got:

1) Find Ipri at 345000V:
Ipri = (kva x 1000)/(V x 1.732) = 1000000/(34500 x 1.732)=16.32 Amps

2) Find Ipri at 480V:
34500/16.73=480/I
Ipri=(480 x 16.32)/34500=0.23 Amps

3) Find Isc at 480V:
Isc=I/Z ≫ Isc=0.23/0.05=4.6 Amps