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hw4_solutions

# hw4_solutions - 2 A transformer is rated at 5(kVA...

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ECE 320: Energy Conversion and Power Electronics Name: Spring 2009 Homework #4 (Due: Monday, March 2, 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 three-phase transformer is made from three single-phase ones, each-rated 40 (kVA), 20(kV)/200(V); rated winding losses 65 (W), core losses 30 (W). The three-phase transformer is connected in Δ at the high voltage side and in Y at the low voltage side. What are the voltage, current ratings, core loss (under rated voltage), winding loss (under rated current) for the 3-phase transformer?

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Unformatted text preview: 2. A transformer is rated at 5 (kVA), 120(V)/20(V). How many autotransformers can be constructed using it? Show the connections and calculate the ratings for each configuration. 3. A DC machine is operated as a generator at 2000 (rpm) without a load and the terminal voltage is 250 (V). When a load is connected, the speed drops to 1600 (rpm), the load voltage becomes 200 (V), and the current is 25 (A). Calculate the torque when the machine operates as a motor at 2100 (rpm) and the applied voltage is 275 (V). I 1 I 1 I 1 I 2 V 1 V 2 V 1 V 2 I 2 V 1 V 2 I 2...
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