The Open University of Sri Lanka
Department of Electrical and Computer Engineering
EEX3410 Introduction to Electrical Engineering - TMA 3 - 2022/2023
Answer all questions. Solutions will be evaluated, through a viva, during the Lab 3 session.
Question 01
a) The renewable sources are freely available for use and the cost for purchasing fuel
for electricity generation is almost zero and the non-renewable energy requires costly
fuel procurement. The shift towards renewable energy gained momentum in the mid2000s and earlier there was not such enthusiasm for renewable sources. Briefly
explain why there was a lack of eagerness to transition towards renewable energy
sources prior to the mid-2000s.
b) Describe the two methods that are used to convert solar irradiation into electricity.
c) What are the transmission voltages in Sri Lanka? The maximum permissible
transmission voltage in the world is typically less than 1200 kV. Is it convenient to
increase the transmission voltages even more than these maximum values? Justify
your answer giving reasons.
d) Ring distribution systems are often preferred over radial distribution systems due to
several advantages. Briefly explain two of them.
e) A 2-wire ring DC distributor (AB) is shown in figure 1. The total length of the ring
distributer is 300 m and it is fed at the point A at 240 V and loads of 120 A and 80A
are tapped off from the positions B (which are at a distance of 150 m from A into the
clockwise direction) and C (which is at a distance of 100 m from A into the anticlockwise direction) respectively, as shown in the picture below. If the resistance of
single conductor per meter is 0.0003 Ω, calculate the currents in each section of the
distributer (IAB, IBC and ICA) and the voltages at point B and C.
IAB
IBC
ICA
Figure 1
Hint
According to Kirchhoff’s voltage law, the voltage drop in a closed loop is zero!
Question 02
A Zener diode voltage-stabiliser is designed with a regulating resistance of 1 kΩ to feed a load
resistance of 1 kΩ. The Zener diode has the following specifications:
• Working (Zenner) voltage VZ = 4.1 V
• Minimum Zener diode current IZ(min) = 1 mA
• Maximum power dissipation PZ(max) = 900 mW
• Zener diode resistance RZ can be neglected
a) Find the range of supply (input) voltage which can safely operate the regulating
circuit.
b) Out of 1/4 W, 1/2 W, 1 W, 2 W and 5 W, what would be the suitable power rating for
the regulating resistor? Justify your answer.
Question 03
a) What is meant by the Operating point (Q-point) of a transistor amplifier? Explain
briefly.
b) Briefly explain how the input affects the output of a transistor in common emitter
configuration when it operates in the following 3 regions:
i. Active region
ii. Cut-off region
iii. Saturation region
c) The common emitter transistor amplifier shown in figure2 is designed to amplify small
signals. Assume VBE = 0.7 V and current gain β = 275
Figure 2
a)
b)
c)
d)
Describe the purpose of the capacitors C1 & C2.
Calculate the base current (IB).
Calculate the collector current IC, Emitter current IE and VCE at Q-point.
Draw the DC load line and mark the operating point (Q-point) on the load line.