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Deapartment of Electrical Enginering
The University of Lahore
Circuit Analysis- 1I (Fall 2015)
Instructor: Hafiz Zaheer Hussain
Submission Date 05-01-
Assignment no 02
Total Marks: 160
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GOOD LUCK
Q-1. 1 A 110-V rms, 60-Hz source is applied to a load impedance Z. The apparent power entering the load is 120 VA at a power factor of 0.707 lagging. (10 Marks) (a) Calculate the complex power. (b) Find the rms current supplied to the load. (c) Determine Z. (d) Assuming that Z = R + j ω L , find the values of R and L.
Q-3 : In the circuit of Fig.1, load A receives 4 kVA at 0.8 pf leading. Load B receives 2.4 kVA at 0.6 pf lagging. Box C is an inductive load that consumes 1 kW and receives 500 VAR. (10 Marks) (a) Determine I. (b) Calculate the power factor of the combination.
Fig. 1
Q-4 Refer to the circuit shown in Fig. 2 (10 Marks) (a) What is the power factor? (b) What is the average power dissipated? (c) What is the value of the capacitance that will give a unity power factor when connected to the load?
Fig. 2
Q-6 : Two loads connected in parallel draw a total of 2.4 kW at 0.8 pf lagging from a 120-V rms, 60-Hz line. One load absorbs 1.5 kW at a 0.707 pf lagging. Determine: (10 Marks) (a) the pf of the second load, (b) the parallel element required to correct the pf to 0.9 lagging for the two loads.
Q-7 : For the Y-Y circuit of Fig.3, find the line currents, the line voltages, and the load Voltages. (10 Marks)
Fig.
Q-9 : Refer to the Δ - Δ circuit in Fig. 5 Find the line and phase currents. Assume that the load impedance is
ZL = 12 + j 9 Ω per phase. (10 Marks)
Fig. 5
Q-10 : A balanced Y-connected load with a phase impedance of ( 40 + j 25 Ω ) is supplied by a balanced, positive sequence -connected source with a line voltage of 210 V. Calculate the phase currents. Use V ab as reference. (10 Marks)
Q.12 A 4200-V, three-phase transmission line has an impedance 4 + j Ω of per phase. If it supplies a load of 1 MVA at 0.75 power factor (lagging), find: (15 Marks) (a) The complex power (b) The power loss in the line (c) The voltage at the sending end
Q.13 The total power measured in a three-phase system feeding a balanced wye-connected load is 12 kW at a power factor of 0.6 leading. If the line voltage is 208 V, calculate the line current and the load impedance 𝑍𝑌 (15 Marks)
Q.15 Assume that the two balanced loads in Fig. 7 are supplied by an 840-V rms 60-Hz line. Load 1 is Y-connected with 30 + j 40 Ω per phase, while load 2 is a balanced three-phase motor drawing 48 kW at a power factor of 0.8 lagging. Assuming the abc sequence, calculate: (20 Marks) (a) the complex power absorbed by the combined load (b) the kVARrating of each of the three capacitors -connected in parallel with the load to raise the power factor to unity (c) the current drawn from the supply at unity power factor condition.
Fig. 7
