(1) A synchronous alternator is supplying 0.9 p.u. power to the grid when a temporary three-phase short occurs on the interconnector. The power angle curves are:-
Pre-fault = 2.0 sin(delta)
During fault = 0.5 sin(delta)
Post-fault = 1.4 sin(delta)
Calculate the critical clearing angle.
(2) A 400-km, 500 kV three-phase transmission line has a series impedance of z = 0.03 + j 0.35 ohms/km and a shunt admittance of y = j 4.4 x 10-6 S/km. Using the equivalent pi circuit calculate the sending end voltage, current and power factor when the line is delivering 1000 MW at unity power factor.
Repeat the calculation using nominal pi circuit and compare and comment upon the difference of the two calculations.