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1 (a) A 66 kV, three-phase, star-connected, short transmission line has a per-phase impedance of (5+j5) 02. If the line supplies a 3-phase, 80 MW load at 0.8 power factor lagging, calculate: Ref.: PC-1 (i) the sending end current; and (ii) the efficiency of transmission. Answers (3 marks) (7 marks) (b) A 3-phase transmission line has the parameters A = D = 121°, B = 80260° 0, and C = j0.0001 S. If an impedance (1 + j20) 02 is connected in series with the line at the receiving end, determine the new parameter values A, B, C and D. (10 marks) Marks
2 A factory having a maximum load of 800 kVA at 0.6 power factor lagging and the load factor is 0.7. The factory is charged with two-part tariff. Given: Maximum demand charge = $80/KVA/annum Energy charge = $0.15 /kWh Capacitor bank charge = $240/kVAr Capacitor bank's interest and depreciation per annum = 10% The factory works 12 hours a day and 200 days a year. Determine: Ref. PC-2 (a) the most economical power factor of the factory; (b) (c) Answers (5 marks) the annual electricity charge when the factory is operating at the most economical power factor; and the annual cost saving. (6 marks) (9 marks) Marks
3 Referring to the below figure, a symmetrical three-phase short circuit fault occurs at Point F. The parameters of the equipment are shown below. (b) Using 100 MVA as the base MVA, determine: Ref. PC-3 (a) (c) (d) (e) (f) (8) (h) (i) Generator (G): 11 kV, 50 MVA, 15% Transformer 1 (T1): 11/132 kV, 10 MVA, 10% Transformer 2 (T2): 11/132 kV, 10 MVA, 5% (j) tot the per unit impedance of Generator (G); the per unit impedance of Transformer (T1); the per unit impedance of Transformer (T2); the per unit equivalent impedance of the system; the fault level in per unit value; the fault level in the unit MVA; the fault current in the unit Ampere; (2 marks) (2 marks) (2 marks) (2 marks) (2 marks) (2 marks) (2 marks) the reactance of the reactor in per unit value if a reactor is added in between the generator G and the 11 kV busbar so that the fault level is limited to 50 MVA; (2 marks) the base impedance (Zb) at the 11 kV busbar; and (2 marks) the reactance of the reactor in Ohms (0) if a reactor is added in between the generator G and the 11 kV busbar so that the fault level is limited to 50 MVA. (2marks)
4 A delta/star connected 132 kV/11 kV 150 MVA Power Transformer (PT) is equipped with a differential protection scheme. The Current Transformers (CT) having a ratio of P:5 are installed at the HV side of the PT while the CTs having a ratio of 1,000:5 are installed at the LV side of the PT. Determine P. (20 marks) Ref. PD-4 Answers Marks