Exam2_03_Sp11_Solution

# Exam2_03_Sp11_Solution - P P Problem 2 (10 Points) Three...

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ELECTRICAL ENGINEERING DEPARTMENT California Polytechnic State University EE 255-03 Exam 2 May 25, 2011 I have neither given nor received unauthorized assistance during this test. Name (Print)_______________________________ Signature:__________________________ Problem 1(15 Points) A 400-V, 60-hz three-phase wye-connected induction motor has a stator impedance of (0.6 + j1.2) , a magnetizing impedance of j35 , a rotor impedance of (0.5 + j1.3) , and mechanical losses of 375 W. Assume a=1.0 and neglect core losses. At a speed of 1140 rpm, calculate the efficiency of the motor. Solution: Let rpm n s 1140 = poles 6 316 6 120 1140 = = = = P P p f rpm n s . rpm p f n s 1200 6 60 120 120 = = = * 05 0 1200 1140 1200 . = - = - = s r s n n n S + = + = ° = + + = 63 3 64 8 8 22 373 9 3 36 10 3 1 10 35 . . . .. . ) . ( j jX R Z j j j Z - ° + V 0 231 0.6 j35 j1.3 j1.2 1 I = 10 05 . 0 5 . 0 Z in Z

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° = + + + = 6 27 43 10 63 3 64 8 2 1 6 0 . . . . . . j j Z in A I ° - = ° ° = 6 27 15 22 6 27 43 210 0 231 1 . . . . A j j I ° - = + ° - = = 2 12 6 20 3 36 10 35 6 27 15 22 2 . . . . . Efficiency W P out 11720 375 0 10 6 20 05 0 1 3 2 = - - = ) . ( ) . )( . ( W P in 13600 6 27 15 22 231 3 = ° = ) . cos( ) . )( ( % . * 2 86 100 13600 11720 = = = in out

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Unformatted text preview: P P Problem 2 (10 Points) Three single-phase transformers each rated 2000-KVA, 33,000:3,300-V, and 60-Hz are connected in wye-delat configuration. The three-phase transformer is supplying a three-phase rated load of 6000 KVA at 3300 V line-to-line and unity power factor. Determine the magnitudes of the LVS and HVS line and phase voltages and line and phase currents. Assume ideal transformers. Solution: LVS A L A I V V V Line ph Line ph 1050 606 * 3 606 3 . 3 * 3 2000 * 3 3300 = = = = = = HVS A L A I V V V V Line ph Line ph 6 . 60 6 . 60 33 * 3 2000 * 3 57158 33000 * 3 33000 = = = = = = Low Voltgae Side (LVS) High Voltgae Side (HVS)Y V ph V Line I ph I Line V ph V Line I ph I Line 3300 V 3300 V 606 A 1050 A 33000 V 57158 V 60.6 A 60.6 A...
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## Exam2_03_Sp11_Solution - P P Problem 2 (10 Points) Three...

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