B 52046 Pages: 3

armature resistance. Draw its phasor diagram also.
11 a) How do harmonics affect the emf generated in an alternator? What are the (4) techniques
used to minimise these harmonic voltages in the induced emf?
b) A 3-0, 10 kVA, 400 ۷, 50 Hz, star connected alternator supplies the rated load (6) at
0.8 pf lag. If the armature resistance is 0.542 and synchronous reactance 15 10Q, find
the load angle and voltage regulation.

PART C
Answer any twofull questions, each carries 10 marks.

12 a) Explain the procedure for conduct of slip test using a neat circuit diagram. ( 4) b) The
efficiency of a 3-0, 400 V, star connected synchronous motor is 95 % and it (6 ) takes 24A at
full load, upf. What will be the induced emf and mechanical power developed at full load, 0.9
pf lead. The synchronous reactance is (0.2+ j2 )Q.
13 a) Describe with the help of a neat circuit diagram, the two bright and one dark (4) lamp method
of synchronising an alternator to the AC mains.
b) A 6-001, 50 Hz,3-® induction motor running on full load develops a useful (6)
torque of 150 Nm at a rotor frequency of 1.5 Hz. Calculate the shaft power output.
If the mechanical torque lost in friction is 10 Nm, determine a) rotor copper loss
b) input to the motor c) the efficiency. The total stator loss is 700 W.
14 a) Describe a set of torque slip characteristics of a 3-0 induction motor. Explain the (4) effect
of change in rotor resistance on the characteristics.

b) Two 3-0, 6.6 kV star connected alternators supply a load of 3000kW at 0.8 pf
(6)

lag. The synchronous impedance/phase of machine A is 0.5 + j 10 Q and that of
machine B is 0.4 +j12 ൮. The excitation of machine A is adjusted so that it delivers
150 A at a lagging power factor and the governors are so set that the load is equally
shared between the machines. Determine the current, power factor and induced
emf of each machine.
PART D
Answer any two full questions, each carries 10 marks.
15 a) What is “Crawling” in induction motors? What are its causes and how can it be (5 )
eliminated?
b) Draw the equivalent circuit of a 1-60 induction motor and explain how it is used (5) to

predetermine the performance of the machine.

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