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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
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_ _ 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 threewire (not balanced 3phase) load shown below. Afﬂfpt ? g4;306 A 72ﬂ~ ' 203L33— 2 a
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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 threephase real
power consumed by this load? (12 points) b) What value of E , if any, will produce balanced threephase 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 ’ :
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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, 3phase source at 208 Volts (RMS Line
Line). Load #1: Deltaconnected load with 12 Amps phase current at 0.9 power factor lag
Load #2: Wyeconnected 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 ‘
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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 Maggirag; @124 Va (“QM/e V ml WWWAKEWWA‘ Problem 4. (25 points) A twocoil system is shown below. You can neglect the leakage ﬂux, but the core has some reluctance that you need to compute. “magmakw. 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‘6at' 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.
 Spring '08
 Kim
 Electromagnet

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