A 200 MW generator is connected to a 138 kV system with two transmission lines as shown below. With the strongest line out of service, the 138 kV system Thevenin impedance is j0.20 per unit on a 100 MVA base. Following closing into a close-in three-phase fault on the strongest line, determine the critical clearing time for this fault condition. (20 pts.)
To be conservative, assume the system equivalent voltage is at 1.0 / 0 deg. Vpu. Assume the power flow is 200 MW and OMvar at the equivalent system voltage.
GSU: 20 kV to 138 kV, Impedance = 9% @ 200 MVA
Generator: 20 kV, 200 MW, Xd = 20% @ 200 MVA, H = 4.0 @ 200 MVA
GSU