B B4811 Pages: 2

Reg No.: Name:

APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
FOURTH SEMESTER B.TECH DEGREE EXAMINATION, APRIL 2018
Course Code: EE202
Course Name: SYNCHRONOUS AND INDUCTION MACHINES (EE)

Max. Marks: 100 Duration: 3 Hours
PART A

Answer all questions, each carries 5 marks. Marks

1 Two alternators run on the same shaft (i.e, runs at same speed). One generates (5)

voltage at 50 Hz and the other at 40 Hz. Find the maximum possible speed. Also
find another possible speed.

2 Draw the phasor diagram of cylindrical rotor alternator supplying leading current (5)
and develop an expression for induced emf E.
3 The excitation of an alternator is running on an infinite bus is steadily increased (5)

from a small value over a wide range keeping the power output constant. By
drawing phasor diagram show the magnitude armature current decreases to a
minimum value and then increases.

4 In rice/flour mills driven by squirrel cage induction motors, the hopper is loaded (5)
with the grains only after starting the motor. Similarly, the delivery valve of
centrifugal pumps driven by squirrel cage induction motor is opened only after
starting the motor. What is the reason behind this? Justify your answer with a
relevant performance curve of squirrel cage induction motor.

5 No load and blocked rotor tests on induction motor are effectively open circuit (5)
and short circuit tests. Justify.

6 Name the induction motor used to drive lifts. What property of this makes it (5)
suitable to drive lifts? How this property is achieved.

7 Using equivalent circuit justify that induction machine becomes a generator (5)
when the machine is driven above synchronous speed.

8 Show the construction of one pole of a shaded pole induction motor and explain (5)
how it produces a sweeping flux when an alternating current flow through the
winding.

PART B
Answer any two full questions, each carries 10 marks.

9 The armature of 60Hz 11kV 450 rpm star connected alternator has 8 conductors (10)
per slot. The winding is short chorded by 3 slots to eliminate 51 harmonics
completely. Find the flux per pole to generate rated voltage on open circuit.

10 a) Prove that even harmonics will not be present in a full pitched winding. (5)
b) Give the procedure for experimental determination of synchronous impedence. (5)
11 In an alternator a field current of I amp was required to drive rated current on (10)

short circuit and a field current of 2.5 times I was required to develop rated
voltage on open circuit. Using emf method find the voltage regulation of the
alternator when delivering rated current at 0.8 pf lag. Assume armature resistance

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