Question

A 100 MVA, 13.2 kV three phase generator (G) having a synchronous reactance of 10% is connected to a three phase Y-Y transformer T1 which feeds a 132 kV 10 miles transmission line having an impedance per phase of 2 + j5 ?/mile. At the receiving end of the transmission line is a Y-Y step down transformer T2. Three loads are connected to the secondary side of the transformer T2. Loads are as follows:

Load#1 40 MVA at 0.8 pf lagging

Load #2 15 MVA at 0.75 pf lagging

Load #3 20 MVA at 0.7 pf leading

The transformer ratings are as follows:

Transformer T1: 120 MVA, 13.2/132 kV, XT1 = 12%

Transformer T2: 100 MVA, 138/33 kV, XT2 = 15%

(i) Draw a one-line diagram for the above power system showing all the equipment parameters, loads and the transmission line.

(ii) Using a base of 100 MVA and a voltage base of 33 kV in the load side of the circuit, draw an impedance diagram of the system expressing all the values in per unit.

(iii) If the load voltage is maintained at 33 kV, calculate the current drawn by the load and the current flowing in the transmission line in per unit and actual.

(iv) Calculate the per unit and actual voltage at the generator terminals.

(v) Calculate the per unit and actual voltages at the beginning of the transmission line and at the end of the transmission line.

(vi) Calculate the active and reactive power delivered by the generator in per unit and actual values.

Answer 1