Download PTU (Punjab Technical University) B.Tech (Bachelor of Technology) / BE (Bachelor of Engineering) 2021 January EE 5th Sem 70554 Synchronous Machines Previous Question Paper
Total No. of Pages : 02
Total No. of Questions : 18
B.Tech. (EE) PT (2012 Onwards) (Sem.?5)
SYNCHRONOUS MACHINES
Subject Code : BTEE-501
M.Code : 70554
Time : 3 Hrs. Max. Marks : 60
INST RUCT ION TO CANDIDAT ES :
1 .
SECT ION-A is COMPULSORY cons is ting of TEN questions carrying TWO marks
each.
2 .
SECT ION-B c ontains F IVE questions c arrying FIVE marks eac h and s tud ents
have to atte mpt any FOUR q ues tions.
3 .
SECT ION-C contains THREE questions carrying T EN marks e ach and s tudents
have to atte mpt any T WO questio ns.
SECTION-A
Answer briefly :
1.
Differentiate salient pole and cylindrical rotor synchronous generators.
2.
Why fractional pitch winding is preferred over full-pitch winding?
3.
Explain the role of damper windings in synchronous generator.
4.
Explain armature reaction of a synchronous machine.
5.
Why is the short circuit characteristics of an alternator is linear?
6.
Why are synchronous motors not self-starting?
7.
What is the effect of increase in excitation of a synchronous motor?
8.
How hunting can be reduced in alternators?
9.
Why are alternators operated in parallel?
10. Explain infinite bus-bars.
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SECTION-B
11. Derive the expression for (i) pitch factor and (ii) distribution factor.
12. Draw and explain the phasor diagram of a loaded alternator for loads at lagging power
factor.
13. Explain the Poteir triangle method of finding regulation of an alternator.
14. Draw and explain the equivalent circuit of a synchronous motor.
15. Derive the condition for maximum power output of a synchronous generator connected to
infinite bus-bar and operating at constant excitation.
SECTION-C
16. Calculate the rms value of the induced emf per phase of a 10-pole, 3-phase, 50 Hz
alternator with 2 slots per pole per phase and 4 conductors per slot in two layers. The coil
span is 150?. The flux per pole has a fundamental component of 0.12 Wb and 15% third
harmonic component.
17. A 3-phase, star-connected, 1000 kVA, 11 kV alternator has rated current of 52.5 A. The ac
resistance of the winding per phase is 0.45 . The test results are given below:
OC Test: Field current = 12.5 A, Voltage between lines = 422 V
SC Test: Field current = 12.5 A, Line current = 52.5 A
Determine the full load voltage regulation of the alternator (i) 0.8 pf lagging and (ii) 0.8 pf
leading.
18. A 3-phase, 415 V, 6-pole, 50 Hz star-connected synchronous motor has emf of 520 V
(L-L). The stator winding reactance of 2 per phase, and the motor develops a torque of
220 Nm. The motor is operating at 415 V, 50 Hz bus.
a) Calculate the current drawn from the supply and its power factor.
b) Draw the phasor diagram showing all the relevant quantities.
NOTE : Disclosure of Identity by writing Mobile No. or Making of passing request on any
page of Answer Sheet will lead to UMC against the Student.
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This post was last modified on 26 June 2021