Question: A 3-phase synchronous generator is joined to a step-up transformer T1, which is joined to a 60 km long transmission line. As the far end of line, a step-down transformer bank T2 is joined. The secondary of T2 supplies the two loads L1 and L2.
The ratings for the different parts of the system are as shown below:
Generator: 10 MVA, 12kV, X = 20%, star connected
T1: 5 MVA, 12/69 kV, X = 10%
T2: 5 MVA, 69/4.16 kV, X=10%
L1: 2000 kVA at 0.8 pf lagging
L2: 1000 kVA at 0.75 pf lagging
Transmission Line: X = 0.5 W/km (R is negligible)
A) Draw the per-phase equivalent circuit of power system showing all the reactance in per unit and show the base voltages employed at different parts of the network by using 10 MVA and 12 kV as base quantities in the generator circuit.
B) If the voltage on load busbar should be maintained at 4.16 kV, find out the required excitation on the generator.
C) For this excitation, find out the short circuit current (in amperes) if a three-phase fault takes place on the secondary winding of transformer T2.