Hong Kong Community College 2018-2019 Semester 2
SEHH2288 Aircraft Electricity and Electronics
Assignment #2
Due Date & Time: 10May20 11:59pm
Instructions
1. Answer ALL questions. Total marks for this assignment is 100 point accounting for 12% of the
continuous assessment.
2. Show all your workings clearly and neatly. Reasonable steps should be shown.
3. Submit your completed assignment on Moodle in a SINGLE PDF file with filename “2288-S2-A2- xxxxxxx(your ID).pdf ”
4. Plagiarism will be penalized severely. Marks will be deducted for assignments that are plagiarized in whole or in part, regardless of the sources.
5. Check the “Declaration of Original Work” on Moodle. Without doing so, you will obtain ZERO mark for your assignment.
6. Students are required to ensure the submitted assignment is correct and intact. Subject lecturer does not have the responsibility to check the correctness of your submitted assignment before marking.
7. Late submission after the deadline will be deducted by 10 marks per day. If the late submission is less not 24 hours, it will be counted as a day.
8. Correct your final answer to 3 Significant Figures.
Expected Learning Outcomes
1. AC power, power factor and three-phase circuits
2. Analysis of transient responses
3. Semiconductors, diodes, zener diodes and their applications
4. Functions of transformers
Student Name
Student ID No.
(Mark N under the last non-zero digit)
Total Marks:
/100
Q1 (20)
Q2 (20)
Q3 (20)
Q4 (20)
Q5 (20)
SEHH2288 Assignment#2 2019-20 SEM2
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IMPORTANT:
Each student is required to complete this assignment individually using her/his student ID number. The method is shown below.
N = the 8th digit of your student ID number. N is a non-zero digit. If the 8th digit is zero, use the 7th digit for N.
Example:
– If your ID number is 12012345A, then N = 5.
– If one of the problems given that a resistance of the circuit is N Ω. This means that the resistance is given as 5 Ω.
Q1. (20%)
If the voltage and current supplied to a load by a source are: 𝑽̃𝒔 = 170∠ 0.157 V; 𝑰̃𝒔 = 13∠− 0.240 A
Determine:
(a) The impedance of the load. What type of load it is? (3%)
(b) The complex power S with correct unit. (3%)
(c) The power factor angle and power factor. (2%)
(d) The power supplied by the source which is dissipated as heat or work in the load,
with correct unit. (3%)
(e) The power stored in reactive component in the load with correct unit. (3%)
(f) An engineer wants to correct the power factor to 0.9. What should be the component
he needs to connect in parallel with the load? What is the value of this component if the frequency of voltage is at 10xN Hz? (6%)
SEHH2288 Assignment#2 2019-20 SEM2
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Q2. (20%)
(a) Athree-phaseAPUisdeliveringpowertoaWye-balancedloadasshownbelow.
Giventhat:R1 =R2 =R3 =N,L1 =L2 =L3 =20mH;ω=2πx60rads-1
(i) Show that IN = 0. (4%)
(ii) Using per-phase analysis, find 𝑰𝑹, 𝑰𝑾 and 𝑰𝑩 in phasor polar. (6%)
(b) Belowshowsacircuitwithanidealdiode:
̃̃̃
NΩ
b
a
12V
10Ω +
4Ω
+ 3V –
5Ω –
(i) Draw the Thevenin equivalent circuit at the terminals a and b. (5%)
(ii) Hence determine whether the diode is forward or reverse biased and find the current through the diode. (5%)
SEHH2288 Assignment#2 2019-20 SEM2 Page 3
Q3. (20%)
For the circuit below, the switch is at position1 for a long time until steady state is reached. At t=0, the switch is turned to position2 such that the charged capacitor is discharged through R1.
R
1
2
R1 C
Vs
(a) Giventhat:Vs=8V,R1 =200,C=100xNμF
(i) Find the capacitor voltage and energy stored at steady state at t = 0-. (3%)
(ii) For t > 0s, write the 1st order differential equation (ODE) of the capacitor voltage,
Vc(t). (4%)
(b) Solve the ODE in part (b) to find the complete transient response of the capacitor voltage for t > 0s. (6%)
(c) Sketch the capacitor voltage against time starting from t = -1s. (3%) (d) Find out the time required to discharge to 4V from t = 0s. (4%)
SEHH2288 Assignment#2 2019-20 SEM2 Page 4
Q4. (20%)
(a) The following circuit is a simple DC power regulator using a Zener diode:
Given:
Vs = 20V, R = 200, VZ = 12V Minimum zener current IZ = 5mA
Calculate:
(i) The maximum load (i.e. minimum RL) that we can connect such that VL = 12V. (4%)
(ii) The power dissipated by the zener diode at maximum load. (2%)
(iii) The minimum load (i.e. maximum RL) if the maximum allowable power of the diode
is 100+10xN mW. (5%)
(b) AnNTC(Negative-TemperatureCoefficient)thermistorisattachedtotheNi-Cd battery of the aircraft and the change of the resistance is detected through the Wheatstone bridge circuit as shown below:
(i) What is the short point of the Ni-Cd battery that makes measurement of battery temperature is essential in the aircraft? (2%)
(ii) Using voltage divider rule, find Vout in terms of R2, R3, R4, RT and Vs if 𝑽𝒐𝒖𝒕 = 𝑽𝒂 − 𝑽𝒃. (4%)
(iii) At 40 C, calculate the output Vout. The values of the Wheatstone bridge circuit components are, Vs = 5 V, R2 = R3 = R4 = 15 kΩ and thermistor resistance can be found in the table above. (3%)
SEHH2288 Assignment#2 2019-20 SEM2 Page 5
Q5. (20%)
(a) BelowistheACcircuitwithatransformer.Theturnratiois1:4.
R1 = 10, R2 = 64,C = 0.008F, L = 16H, Vs = 10xN cos(20t). Zeq R1 C R2
1:4
Source i(t)
Vs ~+ –
L
(i) Find the impedance of the capacitor and inductor. (2%)
(ii) Draw the equivalent circuit as seen from the primary side. (2%)
(iii) Find out the equivalent impedance Zeq as seen from the voltage source. (4%)
(iv) Hence calculate the current i(t) in time domain. (3%)
(b) Below shows a full-wave rectifier circuit using an ideal transformer and diodes:
Ip
Vp ~+-
200 cos(2π x50t)
Is
Vs
N:1
25
+ –
Vo
(i) Find the secondary voltage Vs(t) which is stepped down.(3%)
(ii) Using ideal diode model, sketch the output voltage Vo (t) for at least 2 cycles. State clearly the period of the signal on the graph.(3%)
(iii) Find the current Ip (t) at the primary side, assuming both voltage and current are with the same phase. (3%)
– THE END –
SEHH2288 Assignment#2 2019-20 SEM2
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