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Electrical Circuits and Machines Question Paper - Jun 17 - Electronics And Telecomm (Semester 3) - Pune University (PU)
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Electrical Circuits and Machines - Jun 17
Electronics And Telecomm (Semester 3)
Total marks: 80
Total time: 3 Hours
INSTRUCTIONS
(1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Draw neat diagrams wherever necessary.
1.a.
Apply mesh analysis & determine current $I_{1}$ & $I_{2}$ :
(7 marks)
00
1.b.
Explain construction & working principle of current transformer.
(5 marks)
00
OR
2.a.
State and explain maximum power transfer theorem.
(4 marks)
00
2.b.
The following readings were obtained from O.C & S.C tests on 8 KVA. 400/120 V, 50 Hz transformer :
(8 marks)
00
O.C. test on LV side 120 V 4 A 75 W
S.C. test on HV side 9.5 V 20 A 110W
Calculate the voltage regulation & efficiency at full load, 0.8 p.f. lagging.
3.a.
Explain the characteristics of D.C shunt motor. Comment on p.f.
(5 marks)
00
3.b.
Output of 3$\phi$, 415 V induction motor running at 2% dlip id 36.775 kW. Determine :
(8 marks)
00
- Rotor speed & slip speed
- Rotor O/P & rotor copper loss
- Efficiency of motor at given loading conditions.
Assume motor is wound for 4-pole &supply frequency to be 50 Hz. Given friction & windage losses are 1500W while stator losses are 3 kW.
OR
4.a.
Explain torque-slip characteristics of 3$\phi$ induction motor. Explain the effect of rotor resistance on its characteristics with the help of diagram.
(7 marks)
00
4.b.
A4 pole, 250 V DC series motor has wave connected armature winding with 1254 conductors. The flux pole is 22 mWb when the motor is taking 50 A. The armature & series field coil resistances are 0.3 $\Omega$ & 0.2 $\Omega$. Calculate the speed & torque of the motor & also power depeloped in watts.
(6 marks)
00
5.a.
What are brushless motors? Explain with neat diagram. Explain the operation of unipolar brushless DC motor.
(6 marks)
00
5.b.
Explain construction, principle & applications of reluctance motor.
(7 marks)
00
OR
6.a.
Compare brushless DC motor with conventional DC motor.
(6 marks)
00
6.b.
What are universal motors? Explain speed-torque characteristics of compensated type & non-compensated type universal motor.
(7 marks)
00
7.a.
What are stepper motors? Explain any one type in detail. State its applications.
(6 marks)
00
7.b.
Compare variable reluctance motor with permanent magnet stepper motor.
(6 marks)
00
OR
8.a.
Explain construction & working of AC servomotor. State its applications.
(6 marks)
00
8.b.
What are induction motors? Explain operating principle of shaded 1$\phi$ induction motor.
(6 marks)
00
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