Download PTU (Punjab Technical University) B.Tech (Bachelor of Technology) / BE (Bachelor of Engineering) 2021 January EEE 3rd Sem 76465 Electrical Machines I Previous Question Paper
Roll No.
Total No. of Pages : 02
Total No. of Questions : 18
B.Tech.( Electrical & Electronics Engg./Electronics & Electrical Engg.)
(2018 Batch) (Sem.?3)
ELECTRICAL MACHINES-I
Subject Code : BTEEE-303-18
M.Code : 76465
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.
Explain Fleming's right hand rule.
2.
On what factors does the eddy current loss depend?
3.
Explain the purpose of compensating winding in a dc machine.
4.
Why is the pole shoe section of a dc machine made larger than its body?
5.
Differentiate between dc shunt and series motor.
6.
Explain open-circuit characteristics of a dc generator.
7.
Define speed regulation.
8.
Why stepped core section is preferred to a square section for transformers?
9.
How is magnetic leakage reduced to a minimum in transformers?
10. List the information obtained from open and short circuit tests of a transformer.
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SECTION-B
11. An iron ring of 20 cm mean diameter having a cross-section of 100 cm2 is wound with
400 turns of wire. Calculate the exciting current required to establish a flux of 1 Wb/m2,
if the relative permeability of iron is 1000. What is the value of energy stored?
12. Derive the expression of emf in a dc machine.
13. Draw speed-torque characteristics of different types of dc motors and mention one
application of each type.
14. In an autotransformer, the power transferred from primary to secondary circuit is partly
by conduction and partly by induction. Explain.
15. What is meant by vector group of transformers? What are the distinguishing features of
different groups?
SECTION-C
16. a) Explain linear commutation.
b) A 4-pole generator has wave wound armature with 722 conductors, and it delivers
100 A on full load. If the brush lead is 8?, calculate the armature demagnetizing and
cross-magnetizing ampere-turns per pole.
17. a) Explain the factors affecting the speed of the dc motor.
b) A dc shunt motor having armature resistance of 0.4 takes armature current of 20 A
on full load and runs at 600 rpm. If resistance of 0.5 is placed in the armature
circuit, find the speed at half the full load torque. What is the ratio of stalling torque
to full-load torque?
18. a) Deduce the expression for load shared two transformers connected in parallel having
unequal turns ratio.
b) The maximum efficiency 100 kVA, 50 Hz, single-phase transformer is 95% and
occurs at 90% of full load at 0.85 pf. If the leakage impedance of transformer is 5%,
find the voltage regulation at rated load 0.8 pf lagging.
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