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Assignment # 01 (Solution) (Sp-2010: Text Book: Chapman) 2/
Problem # 02 (1.19) Figure 2.1 shows a simple single-phase ac power system with three loads. The voltage
source is V = 120 ∠ 00 V and the three loads are:
Z 1 (^) = 5 ∠ 300 Ω Z (^) 2 = 5 ∠ 450 Ω Z 3 = 5 ∠− 900 Ω
Answer the following questions about this power system. (a) Assume that the switch shown in the figure is open, and calculate the current I, the power factor, and the real, reactive, and apparent power being supplied by the source. (b) Assume that the switch shown in the figure is closed, and calculate the current I, the power factor, and the real, reactive, and apparent power being supplied by the source. (c) What happened to the current flowing from the source when the switch closed? Why?
Figure 2. Solution
Assignment # 01 (Solution) (Sp-2010: Text Book: Chapman) 3/
Problem # 03 (2.3) A 1000-VA 230/115-V transformer has been tested to determine its equivalent circuit. The results of the tests are shown below.
All data given were taken from the primary side of the transformer. a. Find the equivalent circuit of this transformer referred to the low-voltage side of the transformer. b. Find the transformer’s voltage regulation at rated conditions and (1) 0.8 PF lagging, (2) 1.0 PF, (3) 0.8 PF leading. c. Determine the transformer’s efficiency at rated conditions and 0.8 PF lagging.
Open-circuit Test Short-circuit Test VOC = 230 V V (^) SC = 19. 1 V
I (^) OC = 0. 45 A I (^) SC = 8. 7 A
POC = 30 W PSC = 42. 3 W
Assignment # 01 (Solution) (Sp-2010: Text Book: Chapman) 5/
Problem # 04 (2.6) A 15-kVA 8000/230-V distribution transformer has an impedance referred to the primary of 80 + j300 Ω. The components of the excitation branch referred to the primary side are R (^) C = 350 k Ωand X (^) M = 70 k Ω. a. If the primary voltage is 7967 V and the load impedance is Z (^) L = 3. 0 + j 1. 5 Ω, what is the secondary voltage of the transformer? What is the voltage regulation of the transformer? b. If the load is disconnected and a capacitor of –j4.0 Ω is connected in its place, what is the secondary voltage of the transformer? What is its voltage regulation under these conditions?
Assignment # 01 (Solution) (Sp-2010: Text Book: Chapman) 6/
Solution
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