Reg. No. :
11278
Question Paper Code :
9
B.E./B.Tech. DEGREE EXAMINATION, APRIL/MAY 2011
Third Semester
21
Electronics and Communication Engineering
EC 2201 — ELECTRICAL ENGINEERING
(Regulation 2008)
Time : Three hours
Maximum : 100 marks
Answer ALL questions
9
PART A — (10 × 2 = 20 marks)
List the conditions for self excitation of DC generator.
2.
Write the conditions for the maximum efficiency of DC motor.
3.
Write the transformer emf equation.
4.
Define all day efficiency of transformer.
5.
Can an Induction Motor run at synchronous speed? Justify your answer.
6.
1φ Induction Motor is not self staring. Why?
7.
Distinguish between cylindrical and projecting pole rotors used in
Alternators.
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9
21
1.
8.
Do stepper motors have internal or external fan?
9.
Distinguish EHVAC and EHVDC transmission system.
10.
Distinguish feeder and distributor.
PART B — (5 × 16 = 80 marks)
(a)
(i)
(ii)
Derive the emf equation of the DC generator when the winding
is lap and wave connected.
A 4 pole generator, having wave-wound armature winding has
51 slots, each slot containing 20 conductors. What will be the
voltage generated in the machine when driven at 1500 rpm
assuming the flux per pole to be at 7 mWb.
(8)
Or
(a)
(ii)
When running on no-load, a 400 V shunt motor takes 5 A.
Armature resistance is 0.5 Ω and field resistance 200 Ω. Find the
output of the motor and efficiency when running on full-load
and taking a current of 50 A. Also find the % change in speed
from no-load to full-load. (8)
(i)
Give the classification of transformer based on primarysecondary arrangement, rating and application.
(8)
(ii)
Obtain the equivalent circuit of a 200/400 V, 50 Hertz, 1-φ
transformer from the following test data :
21
Draw the experimental set up to predetermine the efficiency of
the given DC machine and give the necessary relations to find
the efficiency of the machine while it is running as a motor as
well as a generator. Also list the advantages and disadvantages
of
the
test.
(4 + 4)
9
12.
(i)
21
(b)
(8)
9
11.
OC Test : 200 V, 0.7 A, 70 W on LV. side
SC Test
: 15 V, 10 A, 85 W on H.V. side.
(8)
Or
(i)
Explain the operation of the 1φ transformer under load
condition with necessary phasor diagram.
(8)
(ii)
The primary and secondary windings of a 40 KVA, 6600/250V,
1φ transformer has resistances of 10Ω and 0.02Ω respectively.
The leakage reactance of the transformer referred to the
primary is 35Ω. Calculate the full-load regulation at upf and 0.8
lagging pf. Neglect the no-load current.
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9
(b)
13.
(a)
(i)
Explain the principle of production of Rotating magnetic field in
3φ Induction motor with necessary diagram.
(8)
(ii)
Draw the slip-torque of 3φ Induction motor and explain the
significance of it.
(8)
2
11278
(8)
Or
14.
(a)
Name the different types of starters used for 3φ Induction
motor. With necessary diagram explain the principle of
autotransformer starter and find the relation between starting
and full load torques.
(8)
(ii)
Find the % tapping required on an autotransformer required for
a squirrel-cage motor to start the motor to start the motor
against 25% of full-load torque. The short-circuit current on
normal voltage is 4 times the full-load current and full-load slip
is 3%.
(8)
(i)
Derive the emf equation of alternator incorporating various
factors namely form factor, pitch factor and distribution factor.(8)
(ii)
An alternator has 18 slots / pole and the first coil lies in slots 1
and 16. Calculate the pitch factor for fundamental and third
harmonics.
(8)
9
(i)
21
(b)
(b)
(i)
15.
(a)
What are stepper motors? List the various types of stepper
motors. Also define step angle.
Explain any one type of stepper motor in detail with connection
diagram and different operating modes.
(10)
21
(ii)
9
Or
Draw the single line diagram showing the structure of electric power
system and explain each component in detail.
(16)
Or
(i)
With specification, give the layout of a 33/11 KV, sub-station. (8)
(ii)
Draw any one type of insulator and explain about it in brief.
(8)
——————
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9
(b)
3
11278
(6)