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2045

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Electrical Engineering

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Feb 20, 2024

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Power Transformers EECE2115 Solutions for Assignment #7 Page 1 of 2 1. Two transformers are connected in parallel. The connected load is 200 kW, pf =0.95. The transformers have a turns ratio of 5:1. Output voltage is 120 volts. The efficiency of the Transformers is 92%. Calculate the following: a. Output Apparent Power. S 2 = P 2 / pf = 200000 / 0.95 = 210526VA b. Input Voltage. a = 5.0, V 1 = V 2 • a = 120 • 5.0 = 600V c. Input Real Power P 1 = P 2 • 100 / = 200000 • 100 / 92 = 217.391kW d. Input Apparent Power S 1 = P 1 / pf = 217.391 / 0.95 = 228.833kVA e. Output Current (to the load). I 2 = S 2 / V 2 = 210526 / 120 = 1754.386A 877.193A on each f. Input Current (supplying both transformers). I 1 = S 1 / V 1 = 228833 / 600 = 381.388A 190.694A on each g. Current supplied by Transformer 1 to the load. 877.193A on each 2. Two transformers are connected in parallel. The connected load is 3000 kW, pf =0.9. The transformers have a turns ratio of 6:1. The secondary voltage is 4160V. The efficiency of the Transformers is 97%. Calculate the following: a. Primary voltage on each transformer. a = 6.0, V 1 = V 2 • a = 416 0 • 6.0 = 24960V b. Secondary current on each transformer. S 2 = P 2 / pf = 3000 / 0.9 = 3333.3kVA I 2 = S 2 / V 2 = 3333.3(10 3 ) / 4160 = 801.282A 400.641A on each c. Input real power. P 1 = P 2 • 100 / = 30000 00 • 100 / 97 = 3092.784kW d. Input current on each transformer. S 1 = P 1 / pf = 3092.784 / 0.9 = 3436.426kVA I 1 = S 1 / V 1 = 3436.426(10 3 ) / 24960 = 137.677A 68.839 A on each
Power Transformers EECE2115 Solutions for Assignment #7 Page 2 of 2 3. A transformer primary current is measured as 100A. The primary voltage is 27600 and has a turns ratio of 46:1. The efficiency of the transformer is 94% and the pf is 0.83. Calculate the following: a. Secondary voltage. a = 46.0, V 2 = V 1 / a = 27600 / 46.0 = 600V b. Supply (VA) S 1 = V 1 I 1 = 27600 100 = 2760kVA c. Connected load (VA) S 2 = S 1 / 100= 2760 94 / 100 = 2594.4kVA d. Connect Load (W) P 2 = S 2 pf = 2594.4 0.83 = 2153.352kW e. Load Current. I 2 = S 2 / V 2 = 2594.4(10 3 ) / 600 = 4324.0A 4. The load current measured is 85A and the pf = 0.88. The primary voltage is 13800 and has a turns ratio of 3.317:1. The efficiency of the transformers is 96%. Calculate the following: a. Secondary voltage. a = 3.317, V 2 = V 1 / a = 13800 / 3.317 = 4160V b. Connected load (VA) S 2 = V 2 I 2 = 4160 85 = 353.6kVA c. Connected load (W) P 2 = S 2 pf = 353.6 0.88 = 311.168kW d. Supply (VA) S 1 = S 2 • 100 / = 353.6 • 100 / 9 6 = 368.333kVA e. Supply (W) P 1 = P 2 • 100 / = 311.168 • 100 / 9 6 = 324.133kW f. Input Current I 1 = S 1 / V 1 = 368.333(10 3 ) / 13800 = 26.691A
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