Unimelb Foundations of Electrical Networks Exam Paper

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THE UNIVERSITY OF MELBOURNE
Semester 2 Assessment November 2012 Department of Electrical and Electronic Engineering ELEN20005 FOUNDATIONS OF ELECTRICAL NETWORKS Time allowed: 180 minutes Reading time: 15 minutes This paper has 28 pages including the 3-page Formulae Sheet The test is printed single-sided.

Authorised materials:
Only Melbourne-School-of-Engineering-approved (with MSE approval sticker) electronic calculators are permitted.

Instructions to invigilators:
All examination material is to be collected at the end of the exam. Students may use a script book if they run out of writing space on the test paper itself.

Instruction to students:
Attempt ALL questions. The questions carry weight
…show more content…
Be sure to state why energy has been either gained or lost.

=

00

Page 8 of 28

ELEN20005 Foundations of Electrical Networks

Question 5 (10 marks)

12 n

Ie

+ V Rl -

~
20n
100 jlF

24mH

Consider the circuit above at sinusoidal steady state. The source voltage is given to be:

vs(t) = 8 cos(lOOOt) V and is represented by the phasor V s in the circuit diagram. (a) [7 marks] Find the phasor current Ie and the phasor voltage V L. Show all of your work.

Page 9 of 28

ELEN20005 Foundations of Electrical Networks

Question 5 ( Continued)

(b) [3 marks] Draw a phasor diagram indicating the phases of V L, V Rl, and V R2. NOTE: You are required to indicate the exact phase angles of each phasor, but you do not need to determine or label the numerical magnitudes.

Page 10 of 28

ELEN20005 Foundations of Electrical Networks

Question 6 (9 marks)

I



IA
1414/30° V
+
-

IB
8kW 12 kVAR

~A

~

B

10 kVA power factor = 0.7 leading

Two loads, A and B, are connected in parallel with a sinusoidal power source, as indicated in the circuit above. The source voltage phasor is labeled, as is some given power information for each load. (a) [2 marks] Draw and label the power triangle for Load B. Show all of your work.

(b) [2 marks] Find the power factor at the source and indicate whether it is leading or lagging. Show all of your work.

Page 11 of 28

ELEN20005 Foundations of Electrical Networks

Question 6 (Continued)

(c) [2

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