Lehman Engineering Power Quiz
"Overcurrent Protection"
Consider the following distribution line.
A bolted ground fault occurs from CØ to ground at F1:
 G = generator, grounded Y connected (Ignore its impedance in your calculation)
 TX = transformer, 3Ø, Grounded Y Delta , 13.2 kv / 480 volts,
1000 KVA, 3% impedance (ZTX)
 ZXL = system line reactance, ZXL = 2% on 1000 KVA base
 F1 = bolted ground fault from CØ to ground (Assume no fault impedance; ZF1 = 0)
 M = 10 HP, 3Ø, 480 volt, Power Factor = 0.8, Transient Reactance (x'd) = 5%
 (All impedances are on 1000 KVA base and 480 base volts)
Question #1:
Calculate the short circuit current for the ground fault at F1.
Question #2:
What current will flow in the unfaulted phases (A & B) during the fault?
Hint: Remember that the transformer secondary is Delta connected.
