Kaplan Afternoon #27

[cabbagekid2]

2 single phase transformers are connected in parallel with their primaries connected to a 25kV supply. Transformer 1 is rated at 600kVA, 25,000/600V and transformer 2 is rated at 500kVA, 25,000/610V. The equivalent impedance are 0.02+j0.05pu and 0.02 +j0.06 pu, respectively, based on 600kVA, 25kV. The no load circulating current is.....

Answer given: 82A

I understand how they got the circulating current in per unit (0.1427 ang -70 deg), but I don't quite understand how they got the base current.

In the solution, I base = (600,000VA)/(sqrt3 * 600V)=577.35A. Isn't this the per unit equation to find I base for three phase systems? Since these are single phase transformers, shouldn't the equation be I base = (600,000VA)/(600V)?

Thanks again...good luck everyone!

 

[agabee]

2 single phase transformers are connected in parallel with their primaries connected to a 25kV supply. Transformer 1 is rated at 600kVA, 25,000/600V and transformer 2 is rated at 500kVA, 25,000/610V. The equivalent impedance are 0.02+j0.05pu and 0.02 +j0.06 pu, respectively, based on 600kVA, 25kV. The no load circulating current is.....
Answer given: 82A

I understand how they got the circulating current in per unit (0.1427 ang -70 deg), but I don't quite understand how they got the base current.

In the solution, I base = (600,000VA)/(sqrt3 * 600V)=577.35A. Isn't this the per unit equation to find I base for three phase systems? Since these are single phase transformers, shouldn't the equation be I base = (600,000VA)/(600V)?

Thanks again...good luck everyone!

yes. another error from kaplan. i spent some time figuring this out and could not see why my answer was not there. i was not looking at the Kaplan solution. btw an example is in grainger.

 

[cabbagekid2]

Thanks! I just want to make sure I got everything in line before the test tomorrow. I agree with everyone that Kaplan sucks and is not a good thing to be looking at right before the test since you don't know if they're right or wrong.