Jawaharlal Nehru Technological University Kakinada 2008 B.Tech Electronics and Communications Engineering electrical technology - Question Paper

one kind.
(b) A 250W, 230V, 50Hz capacitor begin motor has the subsequent constants for
the main and auxiliary windings: Zm=(4.5+j3.7)ohms. Za=(9.5+j3.5)ohms.
Determine the value of the starting capacitor that will place the main and
auxiliary winding currents in quardrature at starting.
[8+8]
8. The coil of a moving coil voltmeter is 40mm long and 30mm wide and has 100 turns
on it. The control spring exerts a torque of 240×10-6
N-m. When the de?ection is
100 divisions on full scale and the ?ux density of the magnetic ?eld in the air gap
is 1.0 Wb/m2
, estimate the resistance that must be put in series with the coil to
provide 1 volt per division. The resistance of the voltmeter coil may be neglected.
[16]
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2 of 2Code No: 07A3EC13 Set No. 4
II B.Tech I Semester Regular Examinations, November 2008
ELECTRICAL TECHNOLOGY
( Common to Electronics & Communication Engineering, Electronics &
Instrumentation Engineering, Bio-Medical Engineering, Electronics &
Control Engineering, Electronics & Telematics, Electronics & Computer
Engineering and Instrumentation & Control Engineering)
Time: three hours Max Marks: 80
ans any 5 ques.
All ques. carry equal marks
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1. (a) With reference to OCC of a dc generator, discuss the following:
i. Why is the emf not zero when ?eld current is zero?
ii. Will the residual ?ux induce a voltage in the machine, if speed of the
machine is zero
iii. Why does the slope of the curve change, after a certain value of ?eld
current?
(b) A four pole generator has 48 slots and eight conductors per slot. The useful ?ux per
pole is 30mWb and speed is 800 rpm. obtain the generated emf, if the machine
is wave connected. [9+7]
2. (a) discuss the principle of operation of dc motor with suitable diagram.
(b) elaborate the di?erent methods of speed control of dc shunt motor and discuss
any 1 of them in detail. [8+8]
3. (a) What is an ideal transformer? Draw the no load phasor diagram of trans-
former.
(b) The primary winding of a 50Hz, 1- f transformer has 500 turns and is supplied
from 3300V supply. The secondary winding has 50 turns. obtain the peak value
of the ?ux in the core and the secondary voltage. [8+8]
4. (a) A 25 kVA, 2500/250V, 1- f transformer gave the subsequent test ?gures:
O.C Test (LV Side): 250V 1.4A 105W
S.C Test (HV Side): 105V 8A 320W
calculate the equivalent circuit parameters referred to LV side and HV side.
Also find percentage regulation at full load with 0.8 p.f lagging.
(b) De?ne e?ciency of a transformer. find the condition for maximum e?-
ciency. [10+6]
5. (a) discuss brie?y about principle of operation of 3-phase induction motor
(b) A four pole, three - phase induction motor operates from a supply whose frequency
is 50 Hz. compute
1 of 2Code No: 07A3EC13 Set No. 4
i. The speed at which the magnetic ?eld of the stator is rotating.
ii. The speed of the rotor when the slip is 0.04.
iii. The frequency of the rotor current when the slip is 0.03.
iv. The frequency of the rotor current at stand still. [8+8]
6. (a) Draw the vector diagrams of a loaded alternator.
(b) A 60 KVA, 220V, 50Hz, 1-f alternator has e?ective armature resistance of
0.016 ohms and an armature leakage reactance of 0.07ohms. calculate the
voltage induced in the armature when the alternator is delivering rated current
at a load power factor of unity. [8+8]
7. (a) discuss how a capacitor-start split phase induction motor develops a rotating
magnetic ?eld.
(b) An experimental 120V, 1/4hp ,60Hz split phase motor has the subsequent
locked rotor parameters referred to the main and the auxiliary windings.
Rmax=3.94ohms Xmw=4.20ohms
Raw=8.42ohms Xaw=6.28ohms
Determine:
i. Locked rotor current drawn by every winding
ii. Line current at locked rotor. [8+8]
8. (a) define the general requirements for a material to be used for shunts for
ammeters and multipliers for voltmeters for PMMC instruments.
(b) elaborate the commonly used materials and define their properties as regards
to their suitability to be used for shunts or multipliers. [8+8]
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2 of 2

Earning:   Approval pending.