 Subject -
ELECTRICAL POWER UTILIZATION #2 (S1E4)
 Year- 2021
 Batch-2017 normal and repeaters.
General instructions
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This question paper contains total of seven (07) questions in eight (8) pages.
Answer any five (05) questions out of seven (07).
Each question carries total of ten (10) sub questions as part –A & part –B.
Each sub questions carries two (02) marks.
Time allocated for entire question paper is three (03) hours.
Start answering each question on a fresh page.
This is an opened book examination.
Q-1A.
(a)
(b)
(c)
(d)
Classify all motors as per their function and voltage source.
Draw a cross section of a dc motor and mark all major components on it.
Briefly explain the main function of each component that you have mentioned.
State the speed governing equation for a separately excited dc motor. Identify the main
parameters with their units.
(e) Hence briefly explain three (3) conventional methods of speed controlling of a dc motor.
Q-1B.
(a) State five (5) basic power electronics switching components with standard symbols that you
have come across.
(b) State four (4) basic power electronics convertors generally used in electrical power utilization at
industry and give a practical application for each category.
(c) What are the two (2) basic types of chopper drives that can be used for dc motor speed
controlling process?
(d) Draw the relevant circuit diagram for each category you have mentioned in Q-1 ( c ) and briefly
explain the operation of each.
(e) By using relevant wave form diagram, obtain an expression for the output voltage of a buck
convertor as a function of duty cycle (D).
Q-2A.
(a) Draw a wave form diagram and phasor diagram for a single phase 230V RMS, 50Hz AC supply
with a resistive load of 5A.
(b) Draw a circuit diagram for single phase half wave control rectification with a single thyristor.
(c) Obtain an expression for output voltage wave form for above Q-2A-C in terms of triggering
angle -α.
(d) Draw a circuit diagram for three phase full wave control rectification with a (six) thyristor
bridge.
(e) “Ward Leonard Method of speed control can be achieved by varying the applied voltage to the
armature of dc motor”. Explain it with a proper circuit diagram.
Q-2B.
(a) With the help of proper circuit diagram, briefly explain the speed control method of a ceiling fan
(single phase) with a modern power electronic speed controller.
(b) Draw a cross section of a three phase 400V RMS, 50Hz squirrel cage and wound rotor induction
motor separately and mark all major components on them.
(c) Draw a torque speed characteristics of an induction motor and mark the operating speed with a
fan type mechanical load.
(d) “Variable voltage - variable frequency power electronics method can be applied for speed
controlling of three phase induction motor.” Briefly explain the function of it by using a proper
power electronic circuit.
(e) Draw a circuit diagram for a three phase soft starter that can be used for three phase induction
motor.
Q-3A.
(a)
(b)
(c)
(d)
What is meant by “electric traction”? Give two (2) applications for it.
Draw a circuit diagram of dc series motor and mark all major components on it.
Give three (3) speed control methods for a dc series motor.
Draw a torque speed characteristics of dc series motor and mark the operating speed with a
constant mechanical load.
(e) With an aid of suitable block diagram, briefly explain the operation of diesel electric train with
power electronic control. State the relevant typical engine type of Sri Lanka.
Q-3B.
(a)
(b)
(c)
(d)
Sketch a typical battery operated vehicle and mark all major components on it.
State five (5) different motor types that can be used for battery operated vehicles.
What is meant by “electrification of railway system?”
With a suitable schematic diagram, illustrate the electrification of railway system and how the
supply is given to traction motors from over head live conductors.
(e) What is meant by “bullet trains”? Briefly explain the operating principle of linear motion
system on it.
Q-4A.
(a) With a help of suitable sequential block diagram, show that how an illuminated object is
detected and identified by your eye.
(b) Write down five (5) main physical properties of visible light with related to advance physics.
(c) Show that the dual concept of visible light considering its physical properties by using a named
Venn diagram with intersectional properties.
(d) Classify natural and artificial electric light sources further and give practical example for each.
(e) With a suitable named schematic -circuit diagram, briefly explain the operation of single
fluorescent lamp with inductive ballast.
Q-4B.
(a) With suitable named schematic -circuit diagram, briefly explain the operation of compact
fluorescent lamp (CFL).
(b) By using a suitable chart, compare Fluorescent Lamp (FL), Compact Fluorescent Lamp (CFL) and
Light emitting diodes (LED) considering with their properties of illumination, advantages and
application etc.
(c) Define following terms in related with illumination (lighting technology) and state the unit of
under mentioned measurement if any;
a. Luminous flux (φ)
b. Luminous intensity (I)
c. Illuminance (E)
d. Efficacy.
e. Utilization factor
(d) A small assembly shop 16 m long, 12 m wide and 3 m up to trusses is to be illuminated to a level
of 220 lux. The utilization and maintenance factors are 0.75 and 0.9 respectively. Calculate the
number of lamps required to illuminate the whole area if the lumen output of the lamp selected
is 3,200 lumens. (Basic steps are only sufficient)
(e) State following laws of illumination with suitable sketches :
a. Inverse square law.
b. Lambert’s cosine law.
Q-5A.
(a) What is meant by HVAC system of an industry?
(b) Name five (5) no of applications of heat energy sources in industry.
(c) What is meant by latent heat of ice or water and show them in a graph of entropy versus
temperature?
(d) With an aid of proper schematic -circuit diagram, briefly explain Induction heating process.
State one application of it.
(e) With a rough sketch of labeled micro wave oven, briefly explain the dielectric heat generation
process of it.
Q-5B.
(a) Briefly explain the working principle of typical arc furnace.
(b) What is the purpose of having industrial ventilation system in all industries?
(c) Provide a schematic diagram for air condition and refrigeration cycle and there by mark the
main components of domestic fridge.
(d) What are the different kinds of air condition systems available in commercial and industrial
premises?
(e) Define the term “electric welding” and give five (5) types of electric arc welding.
Q-6A.
(a) Starting from chemical process, state supportive engineering layers sequentially for production
engineering process in an industry.
(b) Define an Electro chemical Process. Give two (2) applications for it. ?
(c) With the help of proper schematic diagram, briefly explain the Electrolytic Refining Process of
Copper.
(d) With the help proper flow chart, show that how Aluminum (Al) metal is produced from Bauxite
following chemical engineering basic principles.
(e) Explain following processes in accordance with basic engineering chemistry.
a. Electro polishing.
b. Electrolytic corrosion.
Q-6B.
(a) What is Energy Management relevant to an industry?
(b) State seven principles for effective energy management in industry.
(c) A 12-kW induction motor has a power factor of 0.75 lagging. If we need to run this motor at a
power factor of 0.90, what will be the size of the capacitor required in kVAR?
(d) What are the benefits of Demand Side Management (DSM)?
(e) Explain future trends of followings in Energy Management process:
a. Computer Application in Industrial Field.
b. Computer-Aided Manufacturing.
Q-7A.
(a)
(b)
(c)
(d)
(e)
What is a Pneumatic System? Give two (2) applications for it. ?
State five (5) advantages of pneumatic systems.
Draw a layout of basic pneumatic system and mark all major components on it.
Draw five (5) main symbols used in an Electro Pneumatic Circuit.
What are the primary logic units that may be used in Pneumatic logic systems?
Q-7B.
(a) What is meant by “PLC”? Give two (2) applications of it in industries?
(b) With an aid of proper schematic diagram, identify all major components of a general basic
PLC.
(c) Briefly explain that how do you connect a Pneumatic System into a general PLC system
which is connected to SCADA system.
(d) What is meant by “Ladder Diagram”?
(e) How do you implement safe operations on Pneumatic System as the officer in charge of
safety in a semi automated factory.
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