ASSIGNMENT (4)
4.1-Two impedances Z1 and Z2 are connected in parallel. The first branch takes a
leading current of 16A and has a resistance of 5 Ohm, while the second branch
takes a lagging current at a power factor of 0.8. The total power supplied is 5.0
KW, and the applied voltage being 100 + j 200 V. Determine the complex
expressions for the branch and total currents and for the circuit constants.
4.2-The circuit depicted in Fig. 4.1draws a current of 13.5A at a lagging power factor
and dissipates 2280W when the voltmeter reading is 225 Volts. Find the values of
R1,X 1 and X2.
Fig.4.1
4.3-For the circuit of Fig.4.2
Fig.4.2
a. Calculate I, VR, VL, and VC,. in phasor form.
b. Calculate the total power factor.
c. Calculate the average power delivered to the circuit.
d. Draw the phasor diagram.
e. Obtain the phasor sum of VR,. VL, and Vc, and show that it equals
the input voltage E.
f. Find VR and Vc using the voltage divider rule .
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4.4 -In the circuit shown in Fig.4.3 determine the value of R required if the current I
is to lag behind the applied voltage V by 90°.
Z1 = 20 + j100 Ohm
Z2 = 50 + j150 Ohm
Fig.4.3
4.5 -The two loads in the circuit shown in Fig.4.4 can be described as follows: Load 1
absorbs an average power of 8 kW at a leading power factor of 0.8. Load 2
absorbs 20 kVA at a lagging power v, factor of 0.6.
(a) Determine the power factor of two loads in parallel.
(b) Determine the apparent power required to supply the loads, the magnitude of the
current, Is, and the average power loss in the transmission line.
(c) Given that the frequency of the source is 60 Hz, compute the value of the capacitor
that would correct the power factor to 1 if placed in parallel with the two loads.
Recompute the values in (b) for the load with the corrected power factor.
Fig. 4.4
4.6– In circuit shown in Fig.4.5, a load having an impedance of 39+j26  is fed
from a voltage source through a line having an impedance of 1 + j4  . The
effective, or rms, value of the source voltage is 250 V.
(a) Calculate the load current I L and voltage VL.
(b) Calculate the average and reactive power delivered to the load.
(c) calculate the average and reactive power delivered to the line.
(d) Calculate the average and reactive power supplied by the source.
.
Fig. 4.5
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4.7 –Determine the series equivalent circuit for the network of Fig. 4.6
Fig.4.6
4.8 -For the network of Fig.4.7
Fig. 4.7
a. Determine YT.
b. Find E and IL .
c. Compute the power factor of the network and the power delivered to the network.
d. Determine the equivalent series circuit as far as the terminal characteristics of the
network are concerned.
e. Using the equivalent circuit developed in part (d), calculate E and compare it with
the result of part (b).
f. Determine the power delivered to the network and compare it with the solution of
part (c).
g. Determine the equivalent parallel network from the equivalent series circuit and
calculate the total admittance YT. Compare the result with the solution of part (a).
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4.9 - Calculate the voltages V1 and V2 for the circuit of Fig.4.8 in phasor form using
the voltage divider rule.
Fig.4.8
4.10 - Calculate the currents I1, and I2 of Fig. 4.9 in phasor form using the current
divider rule.
Fig.4.9
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