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Unformatted text preview: 1 Problem Set #2 Transformers and per unit value 2-1 (Grainger and Stevenson, Jr. Chapter 2, Prob. 2.8) A single-phase transformer rated 1.2kV/120V, 7.2kVA yields the following test results: Open circuit test (primary-open) Voltage V 2 = 120V; current I 2 = 1.2 A; power W 2 = 40 W Short circuit test (secondary-shorted) Voltage V 1 = 20V; current I 1 = 6.0 A; power W 1 = 36 W Determine a) The parameters R 1 = r 1 + a 2 r 2 , X 1 = x 1 + a 2 x 2 , G c , and B m referred to the primary side, Fig. 2.7. b) The values of the above parameters referred to the secondary side. c) The efficiency of the transformer when it delivers 6kVA at 120V and 0.9 power factor. Fig. 2.7 Equivalent circuit for a single-phase transformer with an ideal transformer of turns ratio a = N 1 / N 2 . 2 2-2 (Grainger and Stevenson, Jr. Chapter 2, Prob. 2.10) A single-phase system similar to that shown in Fig. 2.10 has two transformers A-B and B-C connected by a line B feeding a load at the receiving end C. The ratings and parameter values of the components are: Transformer A-B: 500V/1.5kV, 9.6kVA, leakage reactance = 5% Transformer B-C: 1.2kV/120V, 7.2kVA, leakage reactance = 4% Line B: series impedance = (1.5+ j 3.0) Load C: 120V, 6kVA at 0.8 power-factor lagging a) Determine the value of the load impedance in ohms and the actual ohmic impedances of the two transformers referred to both their primary and secondary...
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This note was uploaded on 07/17/2008 for the course ECE 740 taught by Professor Keyhani during the Fall '07 term at Ohio State.
- Fall '07