Aume that the neutrals of the generators are now solidly

Question

The Ozzie Outback Electric Power (OOEP) Company maintains the power system shown in Figure. This power system contains five busses, with generators attached to two of them and loads attached to the remaining ones. The power system has six transmission lines connecting the busses together, with the characteristics shown in Table 13-1. There are generators at busses Bunya and Mulga, and loads at all other busses. The characteristics of the two generators are shown in Table 13-2. Note that the neutrals ofthe two generators are both grounded through an inductive reactance of 0.60 pu. Note that all values are in per-unit on a 100 MVA base.

(a) Assume that a single-line-to-ground fault occurs at the Mallee bus. What is the per-unit fault current during the subtransient period? during the transient period?

(b) Assume that the neutrals of the generators are now solidly grounded, and that a single-line-to- ground fault occurs at the Mallee bus. What is the per-unit fault current during the subtransient period now? during the transient period?

(c) Assume that a line-to-line fault occurs at the Mallee bus. What is the per-unit fault current during the subtransient period? during the transient period?

(d) How much does the per-unit fault current change for a line-to-line fault if the generators are either solidly grounded or grounded through an impedance?

Table 13-1:  Transmission lines in the OOEP system.
From		To	RSE  , pu	X	1 , pu	X 2 , pu	X0 , pu
Bunya		Mulga	0.011	0	.051	0.051	0.090
Mulga		Satinay	0.007	0	.035	0.035	0.090
Bunya		Myall	0.007	0	.035	0.035	0.060
Myall		Satinay	0.007	0	.035	0.035	0.060
Myall		Mallee	0.011	0	.051	0.051	0.110
Mallee		Satinay	0.011	0	.051	0.051	0.090
Table 13-2:  Generators in the OOEP system.
Name	Bus	R (pu)	XS (pu)	X'(pu)	X" (pu)	X2 (pu)	Xg0 (pu)	XN (pu)
G1	Bunya	0.02	1.5	0.35	0.20	0.20	0.10	0.60
G2	Mulga	0.01	1.0	0.25	0.12	0.12	0.05	0.60

Figure- The Ozzie Outback Electric Power Company system.