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hw3-key

# hw3-key - EE 295 Homework 3 Solutions March 3 2010 1...

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EE 295 - Homework 3. Solutions March 3, 2010 1 Readings 1. Chapters 5, 6 and 7 of Bergen & Vittal 2 From the textbook (Bergen/Vittal) 2.1 Problem 5.5 In this problem the feeder is a long medium voltage line (24kV), with Z F = 50+ j 400 feeding a step- down transformer, which in turn feeds a 2.4kV load. The transformer impedance is Z T ( LV ) = 0 . 2+ j 1 (on the load voltage side). The load consumes 200kW at 0.9 lagging power factor. (a) Find the sending end voltage V s : V s = V R + IZ F = nV L + I ( Z F + Z T ( HV ) ) The problem is that we are given Z T ( LV ) not Z T ( HV ) . Therefore it is neccessary to do a conversion to get the transformer impedance reflected on the high voltage side, which we can do from the equations on pp.130-131 in the book: Z T ( HV ) = Z T ( LV ) 1 n 2 = 20 + j 100 Now we can calculate the current in the circuit (reflected to the primary side) and solve: I = P ( nV L )0 . 9 - cos - 1 0 . 9 = 9 . 66 - 25 . 8 V s = nV L + I ( Z F + Z T ( HV ) ) = 26 . 0 . 3 k 8 . 96 (b) Find V R . V R = nV L + IZ T ( HV ) = 23 . 6 kV 1 . 9 (c) Find the total transmission efficiency (including the transformer) P LOSS = | I | 2 R = 9 .

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hw3-key - EE 295 Homework 3 Solutions March 3 2010 1...

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