hw7_solutions

# hw7_solutions - ECE 320 Energy Conversion and Power...

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ECE 320: Energy Conversion and Power Electronics Name: Spring 2009 Homework #7 (Due: Friday, May 1, 2009) Circle or box your answer (don’t forget units). Staple any additional paper used to arrive at your answers to this sheet. 1. A synchronous generator has 6 poles. It is rated 2000 (V), 50 (kVA), with a power factor of 0.9 leading, 60 (Hz). The magnetizing reactance, X m , is 77 ( ), and the ratio of the AC stator equivalent current to the rotor DC is I F / i f = 5. a. Calculate the field current under rated conditions and draw the corresponding phasor diagram. b. Keeping the field the same as for part a. and lowering the power to P = 30 (kW), with the same voltage of 2 (kV), calculate the reactive power, Q , and power factor. Draw the corresponding phasor diagram. 2. A permanent magnet AC machine is connected in a Y configuration. It has 4 poles, a field current I F = 27 (A), and a magnetizing inductance, L m = 20 (mH). a. It is to operate at a torque of 35 (N·m) and at a speed of 3000 (rpm). Calculate the necessary

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