Computational Technique

Figure below shows a single line diagram power system. Draw its impedance diagram without showing their values. Also, redraw the circuit with per unit values in the reactance diagram. Take 5,000 VA base and common system base voltage of 250V.

A 90 MVA 11 kV 3-phase generator has a reactance of 15%. The generator supplies two motors through transformers and transmission line shown in figure below. The transformer $T_1$ is a 3-phase transformer, 100 MVA, 10/132 kV, 6% reactance. The transformer $T_2$ is composed of 3 single phase units each rated at 30 MVA, 66/10 kV with 5% reactance. The connection of $T_1$ and $T_2$ are as shown. The motors rated at 50 MVA and 40 MVA both 10 kV and 20% reactance. Taking the generator rating as base, draw reactance diagram and indicate the reactance in per unit. The reactance of line is $100\ \Omega$.

A voltage source $E_{an}=-120\angle 210^\circ\,\mathrm{V}$ and the current through the source $I_{na}=10\angle 60^\circ\,\mathrm{A}$. Find the values of real power ($P$) and reactive power ($Q$) and state whether the source is delivering or receiving each.