Spring2010_Exam1 - ECE 430 Exam #1, Spring 2010 Name: 5—0...

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Unformatted text preview: ECE 430 Exam #1, Spring 2010 Name: 5—0 / Vb 7L1 W”) 90 Minutes Section (Check One) MWF 10am MWF 2pm 1. 25—325 2. 25\/25 3. if /25 4. 25 , /25 Total /00 /100 m « O Useful information sin(x)=cos(x~90°) [7:27- §=V7'k §3¢=\/§VLIL46 o 1 =J§1 delta — — 0<t9<180 (lag) L ¢( ) ZYzzA/3 ‘uoz4fl.10—7H/m ~180° <6<0(1ead) VL=J§V; (wye) a l _ ._ [CH-dbjSJ-nda ICE-dlz—EJSB-nda mzfl—A MMF—Nz_¢SR _ -_ M ¢ = BA ,1_Lz—N¢ k: 1hp=746Watts LIL2 Problem 1. (25 points) A balanced, symmetrical 208 V (RMS Line to Line), 3—phase, 60 Hz source with ABC sequence is supplying the three-wire (not balanced 3-phase) load shown below. Afflfpt ? g4;306 A 72fl~ ' 203L33— 2 a = ’ D R I /oo ’2'“?!— T w W ’ 00 B “’5 ch' Wigwam—«‘7 : \7 'z’ lame-.4: f; MM. C Resistor R is fixed at 100 Ohms. Impedance 2 is specified as a multiple ER, where E could be positive, negative, or even complex. a) If E = 1, what are the three line current magnitudes, and what is the total three-phase real power consumed by this load? (12 points) b) What value of E , if any, will produce balanced three-phase line currents with this connection? (13 points) w '17 6 f ’ , u 300 Iiof; ZDQLEO» freon 4?)! wt. #AAJ 7L4? 1" l ’ ’ * 6° by 439 flile ’ : Dr] I “5: £;” 115” la WJ/l To 7’0 2.08 [590. 7575 “M” v be figé 55 «JILL: (“f/(“TL ._, 9 ., ~ 1 fig/4 16:2,031L50 “bl/(“*5 I bA‘nhtil 34 55*»(A05 JAE.) Problem 2. (25 pts) Three loads are connected in parallel across a 60Hz, 3-phase source at 208 Volts (RMS Line- Line). Load #1: Delta-connected load with 12 Amps phase current at 0.9 power factor lag Load #2: Wye-connected load with 20 Ohms per phase pure resistance Load #3: Delta—connected load with 3,000 Watts plus 1,500 Vars of power (3 -phase) a) Find the line current magnitude for each of the three loads (8 points) b) Find the source line current magnitude (8 points) 0) Find the value of capacitive VARS (3 -phase) that should be added in parallel to these three loads to make the overall power factor 0.95 lag (9 points). .. Mr ‘ A» Ifiéfipifl I12:ij J l I! z .3 (£120? ‘ “* , 223’ ° [20 x1, + jooo+jnrao 1)) 5m, ZHUZDSL— + ?>< o u s will +3325”! +7ILM300M3/yooc Haunt/757 , (23,31212 [7,819:.E¢zogyf£ 14:35:5’3A H {02 (3 F34 : Q’fi‘r Nb‘d Problem 3. (25 points) A magnetic core with two coils is shown below. Magnetic core reluctance, RC, electrical resistances, R3, R1, R2, and winding turns, N1, N2 are known. a) Label the dots on both coils (4 points) (ft a $17 um! i b) Draw the magnetic equivalent circuit (Neglect leakage flux) (4 points) vs Maggi-rag; @124 Va (“QM/e V ml WWWAKEWWA‘ Problem 4. (25 points) A two-coil system is shown below. You can neglect the leakage flux, but the core has some reluctance that you need to compute. “magma-kw. fig 1 System parameters are: y . 42?“: ” M = 100 N2 = 25 Vs Mean length = 0.4m . Area = 0.005 m2 J- ".........v...m...‘........i yr 2 1000 Coil resistances are negligible 0’: I7OJZ (05 {75500 If a 120 V (RMS), 60 Hz sinusoidal voltage source is applied to coil 1, and a 2 ohm resistor is connected across the terminals of coil 2. Find the following quantities in time domain: a) The magnetic flux, 4), in the iron core (5 points) M5 6 5 W n; {‘1 >4 All: will: Wilt/E (Usfwrsaf) f . . b) The magnetic flux density, B, in the iron core (5 points) A l » é do"; ’ 2.3L 403532;? '9’}? ‘fffimfi ‘ M Smmsfl’ 72m ff a 1 fit 0:,- Mgétg/m 2:) all 0 “2,. {4" ‘9" WI") 3 '25, : ?§z.ootgxzmo (05 2mm” ; m 42 H ml: HZflLWfi 27756? 2 2;; d) The primary coil current, i1 (8 points) R: fix—’- ' {biz 21.215052fiéafi 47x15'7x/000x1065‘ ._ 2r“; = 63%}. [00“]: égggzgmota‘jm 2/7601‘ [.2/ ms 2n‘6a-t' L”, : 2.9% 57AWTIR¢+ 55/052776” 4' 25" 2 ...
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This note was uploaded on 10/05/2010 for the course ECE 329 taught by Professor Kim during the Spring '08 term at University of Illinois, Urbana Champaign.

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Spring2010_Exam1 - ECE 430 Exam #1, Spring 2010 Name: 5—0...

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