Homework_2_2011 - (input voltage, output voltage, and...

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ECE 431 – Electric Machinery Spring 2011 Homework Assignment #2 Due in class on Friday February 4 th , 2010. Note: You are expected to review chapters 2 and 3 as needed. 1. A 1000 VA, 230/115 V single-phase transformer has been tested to determine its equivalent circuit. The following tests were performed on the high-voltage side: Open-circuit test Short-circuit test V oc =230 V V sc =19.1 V I oc =0.45 A I sc =8.7 A P oc =30 W P sc =42.3 W a) Find the equivalent circuit of the transformer referred to the low-voltage side. b) Determine the rated resistive load on the high-voltage side. c) Determine the transformer efficiency at rated conditions and a power factor of 0.8 lagging. d) Three of these transformers are wired together for three-phase operation. With a wye connection on both sides, what are the three-phase ratings? 2. A 10 kVA single-phase transformer is rated for 1000 V input and 240 V output. a) If connected as an autotransformer, what are all possible ratings that can be produced
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Unformatted text preview: (input voltage, output voltage, and apparent power)? b) Can it be used for 1000 V to 240 V conversion with apparent power ratings higher than the nameplate 10 kVA? 3. It has been claimed that an open delta connection has advantages over other transformer arrangements. In this application, two transformers are connected to V ab and to V bc , respectively to perform conversion. Consider the following: Two single-phase transformers, each rated at 10 kVA and 1000 V/500 V are connected in the open-delta configuration. Balanced three-phase voltages are imposed. a) Does this work? Can three-phase voltage be drawn from the low-voltage secondary? b) What are the equivalent three-phase ratings? How do these compare to combined ratings of the two devices? c) If a third transformer is added to complete the delta, how will the ratings change?...
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This note was uploaded on 08/25/2011 for the course ECE 431 taught by Professor Bazzi during the Spring '11 term at University of Illinois at Urbana–Champaign.

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