B D192017 Pages:2

Reg No.: Name:

APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
FOURTH SEMESTER B.TECH DEGREE EX AMINATION(S), DECEMBER 2019
Course Code: EE202
Course Name: SYNCHRONOUS AND INDUCTION MACHINES

Max. Marks: 100 Duration: 3 Hours
Graphs sheets shall be supplied.

PARTA
Answer all questions, each carries 5 marks. Marks
1 Explain the term pitch factor in an alternator and derive an expression for it. Also (5)

discuss the effect of short pitching on harmonics.

2 Define armature reaction. Explain the effect of armature reaction on the terminal (5)
voltage of an alternator at zero leading power factor load.

3 Explain why >५ and X, are different for salient pole alternators whereas they are the (5)
same for the smooth rotor machines.

4 Explain the working of a synchronous condenser. (5)
How would you rate the performance of an autotransformer starter with ೩ DOL starter (5)
used in an induction motor?

6 Equivalent circuit parameters of a 3 phase induction motor can be determined from no (5)
load and blocked rotor tests. Justify.

7 Explain the principle of shaded pole induction motor with suitable diagram. (5)

8 Using equivalent circuit prove that the induction machine becomes a generator (5)

when the machine is driven above synchronous speed.

PART B
Answer any two full questions, each carries 10 marks.
9 ३) Differentiate between salient pole type and cylindrical type alternator with sketches. (5)
b) Derive the EMF equation of an alternator. (5)
10 The open-circuit test data for a 3-phase, 3.5 MVA, 4.16 kV, 50 Hz star connected (10)

synchronous generator are given below.
Open-circuit characteristic:
1,(൧) 50 100 150 200 250 300 350 400 450
Voc (line) (kV) 1.62 3.15 4.16 4.75 5.13 5.37 5.55 5.65 5.75
A field current of 200A is found necessary to circulate full load current on short circuit
of the alternator. The machine supplies full-load at a p.f. of 0.8 lagging. Determine its
voltage regulation by (i) EMF method (ii) MMF method. Neglect resistance.
11 a) Show that the output emf wave of an alternator do not contain even harmonics. (5)
b) Find the distribution factor and pitch factor of a 3 phase 4 pole 24 slots alternator (5)

having its armature coils short pitched by one slot.

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