Download Sathyabama University B.E - EEE Nov 2012 Electrical Machines – II

Register Number
SATHYABAMA UNIVERSITY
(Established under section 3 of UGC Act,1956)
Course & Branch :B.E - EEE
Title of the Paper :Electrical Machines – II
Sub. Code :614402 (2007-08-09)
Date :05/11/2012
Max. Marks:80
Time : 3 Hours
Session :AN
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1.
PART - A
(10 x 2 = 20)
Answer ALL the Questions
Write down the EMF equation of DC generator.
2.
Draw the speed-torque characteristics of a dc series motor.
3.
A transformer has 200 turns on the secondary, the flux has a
maximum value of 0.1Wb and varies sinusoidal with a frequency
of 60 Hz. Determine the value of induced emf in the secondary
4.
Why the rating of a transformer is in KVA?
5.
Why skewing is used for rotor assembly?
6.
What is the condition for maximum torque under starting and
running condition of a 3-phase induction motor?
7.
State the applications of synchronous motor?
8.
What is meant by regulation of an alternator?
9.
Draw the circuit diagram of ac servomotor
10. Explain the principle of operation of Permanent magnet dc motor.
PART – B
Answer All the Questions
(5 x 12 = 60)
11. Explain the two reaction theory applicable to salient pole
synchronous alternators Discuss the slip test for finding Xd and
Xq.
(or)
12. Find the synchronous impedance and reactance of an alternator in
which a given field current produces an armature current of 200
A on short circuit and a generated e.m.f of 50 V on open circuit.
The armature resistance is 0.1 ohm. To what induced voltage
must the alternator be excited if it is to deliver a load of 100 A at
a pf of 0.8 lagging, with a terminal voltage of 200 V.
13. (a) Draw and explain the V curve and Inverted V curves of a
synchronous motor.
(b) Explain the working Principle of 3 phase synchronous motor.
(or)
14. (a) A 500, 1 Phase synchronous motor gives a net output
mechanical power of 7.46 KW and operates at 0.9 pf lagging. Its
effective resistance is 0.8 ohm. If the iron and friction losses are
500 W and excitation losses are 800 W, estimate the armature
current .calculate the commercial efficiency.
(b) A 75 KW,3 phase star connected ,50 Hz ,440v cylindrical
rotor synchronous motor operates at rated condition with 0.8 pf
leading. The motor efficiency excluding field and stator losses, is
95% and Xs =2.5 ohm.
Calculate (i) mechanical power developed (ii) armature current
(iii) Back e.m.f (iv) power angle (v) Maximum or pull out torque
of the motor.
15. Explain the construction, types and rotating magnetic principle of
3 phase Induction motor.
(or)
16. Draw the circle diagram for a 5.6 KW, 400V, 3 phase, 4 pole, and
50HZ slip ring induction motor from the following data:
No load test: 400 V, 6A, cos φ0=0.087.
Short circuit test: 100V, 12A, 720W.
The ratio of primary to secondary terms is 2.62.Stator resistance
per phase is 0.67 OHM and that of the rotor is 0.185 OHM.
Calculate( i) The full load current (ii) Full load slip (iii) Full load
power factor (iv) Maximum power and (v)Maximum Torque.
17. Explain with neat sketches the double field revolving theory for
single phase induction motor.
(or)
18. With neat sketches explain construction and principle of
operation of 1 phase series motor and Universal motor.
19. Explain the construction & principle of operation of permanent
magnetic synchronous motor.
(or)
20. Draw the speed torque characteristics and phasor diagrams of
permanent magnetic synchronous motor and explain.