# PTU B.Tech Electrical Engineering 6th Semester May 2019 71152 COMPUTER AIDED ELECTRICAL MACHINE DESIGN Question Papers

PTU Punjab Technical University B-Tech May 2019 Question Papers 6th Semester Electrical and Electronics Engineering (EEE)-EE-Electrical Engineering

Roll No.
Total No. of Pages : 02
Total No. of Questions : 09
B.Tech.(EE/Electrical & Electronics) (2011 Onwards E-I) (Sem.?6)
COMPUTER AIDED ELECTRICAL MACHINE DESIGN
Subject Code : BTEE-605A
M.Code : 71152
Time : 3 Hrs. Max. Marks : 60
INSTRUCTIONS TO CANDIDATES :
1.
SECTION-A is COMPULSORY consisting of TEN questions carrying T WO marks
each.
2.
SECTION-B contains FIVE questions carrying FIVE marks each and students
have to attempt any FOUR questions.
3.
SECTION-C contains T HREE questions carrying T EN marks each and students
have to attempt any T WO questions.

SECTION-A
1)

a) Name the various types of enclosures used in electrical machines.

c) Derive the emf equation of a single-phase transformer.

d) What are the requirements of an ideal insulating material?

e) What do you mean by dispersion coefficient in an induction motor?

f) What are the factors to be considered for the choice of specific magnetic loading in a
rotating machine?

g) Why air gap of an induction motor is made as small as possible?

h) How will you calculate the transformer weight from its design details?

i) Give a classification of insulating materials.

j) Define distribution factor. Discuss its significance.

SECTION-B
2)
A 3-phase squirrel cage induction motor is designed to have copper bars. If, instead of
copper, aluminium were used for rotor bars, discuss what would happen to its speed,
maximum and starting torques and efficiency under normal operating conditions.
1 | M-71152

(S2)-1593

3)
Calculate the main dimensions for a 250KVA, 3000/400Volts, 50Hz, 3-Phase, Delta /
Star, Core type, oil immersed self-cooled, outdoor type distribution transformer. Assume
4)
Derive the expression of voltage regulation of a single-phase transformer. Also, deduce
the conditions for zero and maximum voltage regulation conditions.

5)
Show that the specific electric loading of a rotating machine is constant provided the
current density, ratio of conductor to slot area, ratio of slot width to slot pitch & the slot
depth are constant.

6)
A 12.0 HP, 4-pole, 3 phase, 50Hz, 440V delta connected induction motor has the
following data.

Effective turns per phase = 214, Diameter of stator = 20cm, Length of stator = 12.5cm,

Radial air-gap on one side = 0.055cm, Gap coefficient = 1.33

Find the air-gap ampere-turns required.

SECTION-C
7)
a) Calculate the magnetizing current of a 3-phase, 415V, 4-pole, 50Hz induction motor

having the following data :

Stator slots = 36, conductors per slot = 36, stator bore = 0.2m, stator core length
= 0.18m, effective gap length = 1.05mm, distribution factor = 0.95, full pitch
winding and iron permeability is infinite.

b) Discuss the different types of cross-sections used in the design of power and

distribution transformers. Find out the net core area for cruciform core in terms of

diameter d.
8)
a) Calculate the main dimensions for a 300 kVA, 5500 / 440Volts, 50Hz, 3-Phase,
Delta/Star, Core type, oil immersed self-cooled, outdoor type distribution
transformer. Assume suitable values for various design constants and specific

b) A transformer at the design stage is found to have a voltage regulation of 7.5%. What

alterations should be made in the transformer design so as to get a voltage regulation

of 5%?
9)
Deduce for a 3-phase induction motor an expression showing the relationship between
HP output, its main dimension, speed, the specific electric and magnetic loadings,
efficiency and power factor. Hence, using this expression, obtain suitable values for the
main dimensions of the stator of a 3-phase, 60HP, 2000V, 50Hz, induction motor with a
wound rotor and to run at about 600rpm.

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