ELECTRO MECHANICAL ENERGY CONVERSION-II

ELECTRO MECHANICAL ENERGY CONVERSION-II
SEM-IV, 2012
B.TECH
UTTARAKHAND TECHNICAL UNIVERSITY
(UTU)

Time: 3 Hours

Total Marks: 100

Attempt any four questions

1. Explain the constructional features of Synchronous Machines.
2. What do you mean by pitch factor in ac windings? Derive its expression.
3. What do you mean by armature reaction? For lagging type of load what will be its nature?
4. What do you mean by synchronizing of Alternators? Why synchronization is necessary?
5. Derive from the fundamental, generalized equation of the EMF generated in the non-salient pole synchronous generator.

Attempt any four questions

1. Discuss the procedure to draw 'open-circuit and short-circuit' characteristics experimentally of a synchronous generator.
2. Is synchronous motor a self starting motor? If not then give its starting methods.
3. Describe V curves and what is their practical importance?
4. What is Hunting phenomenon in Synchronous Machines?
5. What is a Synchronous Condenser? For what purpose it is used in electrical systems

Attempt any two questions

1. Why it is necessary to use starters to start Induction Motors. Explain the different methods of starting Squirrel Cage Induction Motors.
2. A 2200V, 400 kW, 3- Ø star connected synchronous motor has a synchronous impedance of (0.3 + j3Ω)/ ph. Determine the excitation emf and the power angle if the motor works at rated load at 0.8pf leading with an efficiency 0f 94%.
3. Show that when a 3-Ø sinusoidally varying ac supply is fed to the stator of a 3- induction motor, a rotating magnetic field is produced that rotates in the air-gap at the synchronous speed and whose amplitude is 3/2 times the amplitude of phase mmf.

Attempt any two questions

1. Describe in brief the construction and working of double cage induction motor.
2. Discuss pole-changing method of speed control for a 3-Ø induction motor.
3. An 8-pole, 50 Hz, 3-Ø, induction motor develops a maximum torque 0f 150 N-m at 650 rpm. The rotor resistance is 0.6 Ω/phase. Find torque at 4% slip. Neglect stator impedance.

Attempt any two questions

1. Explain the working principle of a 1-Ø induction motor.
   Explain the methods of starting 1-Ø induction motor?
2. Describe, with the help of neat sketch, ac series motor.
   Discuss the principle of operation of ac series motor.
   Explain, why ac shunt motor is not feasible?
3. Write short note on the following:
   (i) Double revolving field theory
   (ii) stepper motor

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