5. Transformer ConnectionA power system includes two transformers: T1 (100 MVA, 110/11 kV, impedance 0.05 pu)and T2 (100 MVA, 11/0.4 kV, impedance 0.06 pu). They are connected in series, with T1stepping down from 110 kV to 11 kV and T2 stepping down from 11 kV to 0.4 kV.a. Determine the per-unit impedance of each transformer on a common base of 100 MVA, 11kV.b. Find the equivalent per-unit impedance of the combined transformer system.c. Calculate the actual impedance in ohms on the 0.4 kV side

1. Transformer Per-Unit AnalysisA power system consists of a generator rated at 500 MVA, 20 kV, and a transformer rated at500 MVA, 20/230 kV with an impedance of 0.01 + j0.05 per unit on its own base. Thetransformer is connected to a transmission line with an impedance of 0.02 + j0.1 per unit ona 230 kV, 500 MVA base.a. Convert the transformer impedance to the generator base.b. Calculate the per-unit impedance of the transmission line on the generator base.c. Determine the total impedance of the system (generator, transformer, and transmissionline) in per-unit on the generator base.

Question 2List three functions which a transformer may perform in an electrical circuit. [3 marks]A 10kVA, 50 Hz distribution transformer has 600 turns in the primary and 120 turns in thesecondary. The primary and secondary resistances are r1 = 0.2 Ω and r 2 = 0.02 Ω respectively,and the corresponding leakage reactances are Xl1 = 1.0 Ω, and Xl2 = 0.04 Ω respectively. Thesupply voltage is 1100V.Calculate(a) The equivalent impedance, resistance and reactance, referring all quantities to thehigh voltage (primary) side; [6 marks](b) The secondary terminal voltage for full load having a power factor of 0.7 lagging;Draw the phasor diagram; [7 marks](c) The regulation in (b) [4 marks]2130310310

60 MVA, 118/69 KV, A/Y (5 A in the secondary side) transformer protected using differential bias relay. (Ove) and (+ve) sequence resistances are 0.69 and 0.556 N/km, respectively. (Ove) and (+ve) sequence inductances are 5.25 and 1.26 mH/km, respectively. i) Draw the transformer connection with the CT and the connection of differential relay. ii) Calculate the CT ratio for both HV and LV sides and the current mismatch? iii) Determine and draw the impedance of the first, second and third zones using the positive sequence impedance only.

6. Multi-Voltage Level SystemA power system includes a generator (500 MVA, 13.8 kV, X'' = 0.2 pu), a transformer (500MVA, 13.8/138 kV, Z = 0.1 pu), and a transmission line (Z = 0.02 + j0.1 pu on 138 kV, 500MVA base). A load of 450 MW at 0.9 power factor lagging is connected at the end of thetransmission line.a. Convert all impedances to a common base of 500 MVA, 13.8 kV.b. Calculate the per-unit voltage at the load bus.

A 3ф load of 3 similar inductive coils, each of resistance 50Ω andinductance 0.34H. The supply voltage is 415v/50Hz. calculate thea) Line current (IL)b) Power factors (P.F.)c) The total power when the load is connected in(a) STAR (c) DELTA CONNECTION