1. You have a power system that consists of a generator, 01, connected to a three-phase step-up delta-to-wye transformer (with neutral grounded), T1, which is connected to a transmission line, LI, which is connected to a three-phase step-down wye-to-delta (wye not grounded) transformer, T2, which is connected to a synchronous motor, MI, that is currently offline. The positive, negative and zero sequence impedance of the generator, GI, is 0.15, 0.15 and 0.05, respectively. Initially, assume that GI has its neutral solidly connected to ground. The transformer T1 has positive, negative and zero sequence impedance given by 0.1, 0.1 and 0.15 respectively. The transmission line, LI, has positive, negative and zero sequence impedance given by 0.1, 0.1 and 0.15 respectively. The transformer 1'2 has positive, negative and zero sequence impedance given by 0.05, 0.05 and 0.1 respectively.
a. Draw the sequence networks for this power system.
b. Assume a SLG fault occurs just beyond the low side of T2. Draw the sequence networks with connections resulting from this fault and solve for the fault current.
c. Assume a SLG fault occurs just before the high side of T2. Draw the sequence networks with connections resulting from this fault and solve for the fault current.
d. Assume a SLG fault occurs right in the middle of the transmission line, LI. Draw the sequence networks with connections resulting from this fault and solve for the fault current.
e. Assume a SLG fault occurs just beyond the high side of T1. Draw the sequence networks with connections resulting from this fault and solve for the fault current.
f. Assume a SLG fault occurs just before the low side of T1. Draw the sequence networks with connections resulting from this fault and solve for the fault current.
2. Repeat problem 1 but this time assume that the generator, GI, has its neutral connected to ground through a 0.02 resistance.
3. Repeat problem 1 but this time assume that the generator, GI, has its neutral connected to ground through a 0.02 reactance.
4. Discuss the effect on fault current magnitude with respect to the three ways that the neutral of generator GI was connected to ground.
Helpful Hints: See the TransformersZeroSequence.pdf file attached . Also, when a generator is connected to ground through impedance, Zg, then the zero sequence network has an impedance of 3Zg added in series with its zero sequence impedance, 4.
Attachment:- TransformersZeroSequence.pdf