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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Autumn Examinations 2011/
Electrical Circuit Analysis
Module Code: ELEC
School: Electrical and Electronic Engineering
Programme Title: Bachelor of Engineering in Electrical Engineering – Year 2
Programme Code: EELEC_7_Y
External Examiner(s): Ms Mary Desmond, Mr Colm Murray Internal Examiner(s): Mr Noel Mulcahy
Instructions: Answer All Questions
Duration: 2 Hours
Sitting: Autumn 2012
Requirements for this examination:
Use of a Scientific Calculator capable of complex notation is permitted.
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
Section A
Q1.
a. Sketch a simple High Frequency Filter and Low Frequency Filter, labelling each clearly and their component parts. (4 marks) b. The following filter was constructed in a Lab Experiment.
10Vrms @ Variable Frequency
2 F
V out
100
Determine the output voltage when a 10V sinusoidal supply of the following frequencies is applied. i. 1 Hz. ii. 10 kHz. (6 marks) c. Determine the phase angle of the voltage w.r.t. the current flowing in the following circuit as constructed in the lab.
36 F 230
115 V @ 50 Hz
A
700 mH
(10 marks)
Q2.
a. Using the following Star connected loads as detailed in the following circuit. Determine the equivalent Delta connected circuit.
(10 marks) b. Sketch a suitable arrangement of Wattmeters to measure the power in the Delta Equivalent Circuit. (10 marks)
Some Useful Formula
Capacitive Reactance
......
1 1 C 2 X j C j f C
[]
Inductive Reactance X (^) L j.. L j.... 2 f L []
Impedance (a)
Z XL XC R []
(b) Z R^2 XL X C ^2 []
(c) Z R j L j C []
Series Circuit:
(a) VT ( V (^) L VC )^2 VR^2 [V]
(b) Z
R
p. f . Cos (power factor)
Parallel Circuit: (a)
IT I 1 I 2 I 3 [A]
(b) EQUIVALENT
T T Z
V
I [A]
(c) ACTUAL
IN PHASE I
I
p. f. (power factor)
Power P V. I. Cos [W] (Single Phase Power)
Time Constant R
L
[s]
Energy stored in an Inductor..^2 2
E LI [J]
^
t Growth of Current in an iL I e [A] Inductor in an RL Network
^
t i (^) L I. e [A]
Star – Delta Transform
A B C
A B Z Z Z
Z Z Z
1 , A B C
B C Z Z Z
Z Z Z
2 , A B C
A C Z Z Z
Z Z Z
3
Delta – Star Transform
2
1 * 2 2 * 3 3 * 1 Z
Z Z Z Z Z Z Z (^) A , 3
1 * 2 2 * 3 3 * 1 Z
Z Z Z Z Z Z Z (^) B , 1
1 * 2 2 * 3 3 * 1 Z
Z Z Z Z Z Z ZC
Decay of Current through an Inductor in an RL Network
