Bugman1400,
The transformer info I was given is as follows:
1000 KVA
34500 V primary
480Y/277V secondary
%Z 5.75
X1/R1 9.74
X0/R0 9.13
LLL Fault Test Data 19921
LN Fault Test Data 19790
Almost without exception, all my Delta to WYE grounded transformer banks have a higher phase to neutral fault duty than the three phase fault duty very near the transformer. This is true due to the Delta side of the transformer supplying an additional current to the single phase faulted low side of the transformer. Adding additional line length to the low side results in enough of an impedance increase to cause the single phase to ground fault to become less than the three phase faulted system. Based on the numbers given for your transformer I get a three phase fault value of 20,910 amps three phase fault and 22,020 amps single phase to neutral fault. I did use an infinite bus to calculate these values but any additional system impedance to the primary side of the transformer will only result in a reduced value for both fault currents but the difference between the 3 phase and 1 phase fault will stay near the 5% value. My positive sequence X1/R1 was 9.817, negative sequence X2/R2 was 9.74 and zero sequence Xo/Ro was 9.13, so what you were given seems OK to me.
Hope this helps,
Newton Law
