Answer number #8 8. A 415-V, 3-phase, 4-wire system supplies power to three non-inductive loads. The loads are25 kW between red and neutral, 30 kW between yellow and neutral and 12 kW between blue and neutral.Calculate (a) the current in each-line wire and (b) the current in the neutral conductor.[(a) 104.2 A, 125 A, 50 A (b) 67 A] (London Univ.)9. Non-inductive loads of 10, 6 and 4 kW are connected between the neutral and the red, yellow andblue phases respectively of a three-phase, four-wire system. The line voltage is 400 V. Find the current ineach line conductor and in the neutral.[(a) 43.3 A, 26A, 173. A, 22.9] (App. Elect. London Univ.)10. A three-phase, star-connected alternator supplies a delta-connected load, each phase of whichhas a resistance of 20 Q and a reactance of 10 Q Calculate (a) the current supplied by the alternator (b) theoutput of the alternator in kW and kVA, neglecting the losses in the lines between the alternator and theload. The line voltage is 400 V.11. Three non-inductive resistances, each of 100 Q, are connected in star to 3-phase, 440-V supply.Three equal choking coils each of reactance 100 2 are also connected in delta to the same supply.Calculate:[(a) 30.95 A (b) 19.2 kW, 21.45 kVA](a) line current(b) p.f. of the system.[(a) 8.04 A (b) 0.3156] (I.E.E. London)12. In a 3-phase, 4-wire system, there is a balanced 3-phase motor load taking 200 kW at a powerfactor of 0.8 lagging, while lamps connected between phase conductors and the neutral take 50, 70 and 100kW respectively. The voltage between phase conductors is 430 V. Calculate the current in each phase andin the neutral wire of the feeder supplying the load.[512 A, 5.87 A, 699 A; 213.3 A] (Elect. Power, London Univ.)13. A 440-V, 50-Hz induction motor takes a line current of 45 A at a power factor of 0.8 (lagging).Three A-connected capacitors are installed to improve the power factor to 0.95 (lagging). Calculate thekVA of the capacitor bank and the capacitance of each capacitor. [11.45 kVA, 62.7 µF] (I.E.E. London)14. Three resistances, each of 500 Q are connected in star to a 400-V, 50-Hz, 3-phase supply. Ifthree capacitors, when connected in delta to the same supply, take the same line currents, calculate thecapacitance of each capacitor and the line current.15. A factory takes the following balanced loads from a 440-V, 3-phase, 50-Hz supply:(a) a lighting load of 20 kW(c) an intermittent welding load of 30 kVA at 0.5 p.f. lagging.Calculate the kVA rating of the capacitor bank required to improve the power factor of loads (a) and(b) together to unity. Give also the value of capacitor required in each phase if a star-connected bank isemployed.What is the new overall p.f. if, after correction has been applied, the welding load is switched on.[2.123 µ F, 0.653 A] (London Univ.)(b) a continuous motor load of 30 kVA at 0.5 p.f. lagging.[30 KVAR; 490µ F; 0.945 kg]16. A three-wire, three-phase system, with 400 V between the line wires, supplies a balanced delta-connected load taking a total power of 30 kW at 0.8 power factor lagging. Calculate (i) the resistance and(ii) the reactance of each branch of the load and sketch a vector diagram showing the line voltages and linecurrents. If the power factor of the system is to be raised to 0.95 lagging by means of three delta-connectedcapacitors, calculate (ii) the capacitance of each branch assuming the supply frequency to be 50 Hz.[() 10.24 A (i) 7.68 2 (ii) 83.2 µF] (London Univ.)

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8. A 415-V, 3-phase, 4-wire system supplies power to three non-inductive loads. The loads are 25 kW between red and neutral, 30 kW between yellow and neutral and 12 kW between blue and neutral. Calculate (a) the current in each-line wire and (b) the current in the neutral conductor.