PTU B.Tech Electrical Engineering 6th Semester May 2019 72838 ELECTRICAL MACHINE 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 Engineering/Electrical & Electronics)
(OE 2012 Onwards) (Sem.?6)
Subject Code : BTEEE-OPA
M.Code : 72838
Time : 3 Hrs. Max. Marks : 60
SECTION-A is COMPULSORY consisting of TEN questions carrying T WO marks
SECTION-B contains FIVE questions carrying FIVE marks each and students
have to attempt any FOUR questions.
SECTION-C contains T HREE questions carrying T EN marks each and students
have to attempt any T WO questions.

Write briefly :

a) Define magnetic field intensity, flux and flux density.

b) What are the core losses and how can this loss be minimized?

c) Define Faraday's Law of Electro Magnetic Induction.

d) What are the conditions for parallel operation of a transformer?

e) Draw the no load phasor diagram of a transformer.

f) Why the Starters necessary for starting DC motors?

g) What is the significance of back emf in a DC motor?

h) What are the various methods available for making single phase motor self-starting?

i) State the advantage of using capacitor start motor over a resistance split phase motor.

j) What are the advantages of cage type induction motor?

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Explain the working principle of synchronous machine with neat diagram.
Draw and explain fully the general block diagram representation of an electromechanical
energy conversion device.
Explain polarity test of single phase transformer with suitable circuit diagram.
Explain the working principle of capacitor start single - phase induction motor. Why
should be the auxiliary winding in a capacitor start motor be disconnected after the motor
has picked up speed?
The peak value of flux density in the core of a 300/ 3000 V, 50 Hz 1 -phase transformer
is 1.4 Wb / m2. If the e.m.f. per turn is 10 volts, calculate:

a) Primary and secondary turns and

b) Area of cross section of the core.

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.
A cage induction motor has a short-circuit current of 4 times the full-load value and has a
full- load slip of 0.05. Determine a suitable auto-transformer ratio if the supply current is
not exceed twice the full-load current. Also determine the starting torque in terms of the
full-load torque.
An 8-pole, 400 V shunt motor has 960 wave connected armature conductors. The full
load armature current is 40 A and flux per pole is 0.02 Wb. The armature resistance is 0.1
ohm and the contact drop is 1 V per brush. Calculate the full load speed of the motor.

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 04 November 2019