Homework_4_2011 - What if the speed is 1880 RPM? 3. A 460V,...

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ECE 431 homework assignment #4 Due in class – Friday, February 25, 2011 1. A 208 V, six-pole, Y-connected, 25 hp, 60 Hz three-phase induction motor is tested with the following test results: No load test: 208 V, 22 A, 1200 W, 60 Hz. Locked-rotor test: 24.6 V, 64.5 A, 2200 W, 15 Hz. Dc test: 13.5 V, 64 A. a. Find and draw the per-phase equivalent circuit of the motor. b. What is the motor efficiency and input electrical power at rated load assuming a unity power factor? c. Find the slip at the maximum torque and plot the torque-speed characteristic curve. 2. A three-phase induction motor has been tested, and has small stator resistance. At 230 V, 60 Hz, the motor produces 40N-m at 1740 RPM. a. Given a 40 N-m load, input of 115 V and 30 Hz, what operating speed do you expect? b. This machine is operated as a variable-speed generator. The external drive imposes 20 N-m on the shaft. The speed is 2400 RPM. Determine the appropriate operating frequency and voltage.
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Unformatted text preview: What if the speed is 1880 RPM? 3. A 460V, four-pole, 50hp, 60Hz, Y-connected three-phase induction motor develops its full-load torque at 3.8% slip when operating at 60Hz and 460V. The per-phase circuit model impedances of the motor are: R s =0.33 , X s =0.42 , X r =0.42 , and X m =30 . Ignore mechanical, core, and stray losses. a. Find the rotor resistance R r . b. Find the maximum torque in addition to the slip and rotor speed at that torque. c. Find the starting torque (slip=100%). 4. A linear induction machine can be potentially used to launch aircraft on short runways. A similar machine is tested at no load by applying 4.6 kV, 400Hz and found to move at 50.0 m/s (180 km/h, ~112 mph). What is the stator spatial wavelength (the physical spacing between two different +A phase windings) for this machine? What voltage and frequency would you suggest to achieve 20 m/s?...
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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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