# PTU B.Tech Electrical Engineering 6th Semester May 2019 72842 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. (Electronics Engg) (E-1 2012 Onwards) (Sem.?6)
ELECTRICAL MACHINE DESIGN
Subject Code : BTEEE-603A
M.Code : 72842
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. What are the "main dimensions" in machine design?

b. What are the factors that affect volume of a three phase induction motor?

c. Define short time and intermittent rating of induction motor.

d. Why machines with large dimensions are more efficient?

e. Write the differences between core and shell type transformer.

f. What is the function of fins on the tank of transformer?

g. Write the function of frame of a three phase induction motor.

h. Which design factors influence the power factors of induction motor?

i. What is peripheral speed of rotating machine?

j. What are the design parameters responsible for increase in starting torque?

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SECTION-B
2.
What are the cooling methods applied for reduction of temperature rise of a transformer?
3.
Derive the output equation for design of a three phase transformer.
4.
Derive the condition for design of minimum cost in a transformer.
5.
Discuss the steps of calculations for designing number of stator slots and area of stator slots
of a three phase induction motor.
6.
A 3-phase, 4 pole induction motor has 24 slots. Calculate the order of slot harmonics
produced. It is desired to completely eliminate the higher order slot harmonic, find the
angle through which the bars must be skewed. Find the effect of skewing on the lower
order harmonic.

SECTION-C
7.
Determine the core dimensions, number of stator slots, number of stator conductors for a
10 kW, 415V, 3-Ph, 4 pole, 50 Hz. Motor. Assume winding factor 0.955, full load
efficiency 0.85, power factor 0.8. For the machine Bav = 0.35 Wb/ m2 ac = 20000 A/m.
Output coefficient C0 = 87.2, L/ = 0.83.
8.
Calculate the approximate overall dimensions for a 100 KVA, 6000/440V, 50 Hz. 3-Ph
core type transformer. Volts/ turn, Et = 10V, Flux density Bm = 1.1 Wb/ m2 , current
density = 2.5 A/ m2 , Winding factor Kw = 0.3, Overall height = overall width, stacking
factor 0.9. Use a 3-stepped core.
9.
Derive the equation of temperature rise with time in electric machines. What is heating
time constant? Briefly discuss about induced, forced, radial and axial ventilation. Write the
advantages of hydrogen cooling in turbo alternators.

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