Download PTU (Punjab Technical University) B.Tech (Bachelor of Technology) / BE (Bachelor of Engineering) 2021 January EE 3rd Sem 76383 Electrical Machines I Previous Question Paper
Roll No.
Total No. of Pages : 02
Total No. of Questions : 18
B.Tech.(EE) (2018 Batch) (Sem.?3)
ELECTRICAL MACHINES-I
Subject Code : BTEE-302-18
M.Code : 76383
Time : 3 Hrs. Max. Marks : 60
INST RUCT IONS T O 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
Write briefly :
1.
Which material is suitable for making permanent magnet? Give reason.
2.
Why laminated core in electrical machines are used?
3.
While comparing magnetic and electric circuit, the flux of magnetic circuit is compared
with which parameter of the electric circuit.
4.
What are the materials used for brushes in dc machines? Also give reason.
5.
What is purpose of field winding in DC machines?
6.
Define back emf in DC motor.
7.
How the effect of armature reaction in DC machine is minimised?
8.
Why DC series motor should not be started without load, explain.
9.
Why transformer is rated in KVA.
10. Draw the phasor diagram of single phase transformer on no load.
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SECTION-B
11. The armature resistance of a 200 V shunt motor is 0.4 and no-load current is 2 A.
When loaded and taking an armature current of 50 A, the speed is 1200 rpm. Find
approximately the no-load speed.
12. Discuss the open circuit characteristics of separately excited DC generator with suitable
diagram.
13. A coil of 100 turns is wound uniformly over a wooden ring. The ring is having a mean
circumference of 500 mm and a uniform cross-section area of 400 mm2. A current of 4 A
passed through the coil. Calculate :
a) Magnetic field strength
b) Flux density
c) Total flux.
14. Explain the principle of operation of dc machine. Derive the expression for the back emf
in a dc motor. Briefly explain the role it plays in starting and running of the motor.
15. Explain the on load operation of single phase practical transformer.
SECTION-C
16. Two DC shunt generators are connected in parallel to supply a load of 5000 A. Each
machine has an armature resistance of 0.03 and field resistance of 60 but the emf of
one machine is 600V and that of the other machine is 640 V. What power does each
machine supply?
17. The emf per turn for a single phase, 2310/220 V, 50 Hz, transformer is approximately
13 Volts.
Calculate :
a) The number of primary and secondary turns.
b) The net cross-sectional area of the core, for a maximum flux density of 1.4T.
18. With suitable circuit diagram, explain open circuit test and short circuit test on single
phase transformer.
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