(a) Three loads are connected in parallel across a 12.47 kV, three-phase, 50-Hz supply. Load 1: Inductive load absorbs 60 kW and 660 kVAr. Load 2: Capacitive load absorbs 240 kW at 0.8 power factor. Load 3: Resistive load absorbs 60 kW. (i) Determine the total complex power, power factor, and the supply current. (5 marks) (ii) A Y-connected capacitor bank is connected in parallel with the above loads. Determine the kVAr rating of the capacitor bank and the capacitance per phase (in µF) required to improve the overall power factor to 0.8 lagging. What is the new value of line current? (5 marks) (b) A 20-kVA, 440/220V, 50 Hz, single phase, two-winding transformer has the following test data: Open Circuit Test (OCT): 220V, 9.5A, 650W Short-circuit Test (SCT): 37.5V, 45.45A, 950W (i) Determine the rated currents in the high voltage and low voltage sides of the transformer. (2 marks) (ii) Determine the parameters of the approximate equivalent circuit of the transformer. (8 marks)
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For Load 1: Apparent power (S1) = √(P1^2 + Q1^2) = √(60^2 + 660^2) = √(3600 + 435600) = √439200 = 662.6 kVA Power factor (pf1) = P1 / S1 = 60 / 662.6 = 0.0905 (lagging) For Load 2: Apparent power (S2) = P2 / pf2 = 240 / 0.8 = 300 kVA Power factor (pf2) = 0.8 Show more…
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