Download AKTU B-Tech 5th Sem 2015-2016 Electromechanical Energy Conversion Ii Eee 501 Question Paper

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Paper ID : 121521

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B.Tech.

(SEM. V) THEORY EXAMINATION, 2015-16

ELECTROMECHANICAL ENERGY CONVERSION-II

Time: 3 hours] [Total Marks: 100

SECTION-A

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1. Attempt all parts. All parts carry equal marks. Write answer of each part in short : (2×10=20)
   1. Why the power factor of the lightly loaded induction machine is quite low?
   2. What do you understand by the term cogging?
   3. Calculate the speed in rpm of a 6 pole induction motor which has a slip of 6% at full load with a supply frequency of 50 Hz. What will be the speed of a 4 pole alternator supplying the motor?
   4. Give application areas of the cylindrical and salient pole type synchronous machine.
   5. What are the reasons for the difference between the results of direct load test and indirect load test on synchronous machines?

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   6. State some important application of the stepper motors.
   7. How will you reverse the direction of rotation of the single phase Induction motor?
   8. From the first principles derive the equivalent circuit of a three phase induction motor. How the mechanical load is separated from rotor copper loss in the equivalent circuit.

SECTION-B

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Note: Attempt any five questions from this section. (10×5=50)

2. Explain the operating principle and constructional aspects of Deep Bar and Double cage Induction motor. Explain how these motors can give higher starting torque in comparison to the conventional design.
3. Show that in a 3 phase induction motor :
   t_max / t_fl = 1 / 2 * (R₂² + s_flX₂) / (ß s_fl)
   where ß = R₂ / X₂

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4. Explain the phenomenon of armature reaction when alternator is delivering a load current at purely leading and purely lagging power factor. Also derive the EMF equation of an alternator.
5. Two identical 2000 kVA, 11 kV, 3-phase star connected alternators runs in parallel with their terminal voltage maintained at 11 kV. The synchronous reactance is 20%. Find for (a) No-Load, (b) Full load at p.f. 0.8 Lagging, synchronizing power per unit mechanical angle of face displacement and calculate the synchronizing torque if mechanical displacement is 0.5 degree.
6. (a) What are the effects of space harmonics in 3 phase induction motors?
   (b) The stand still impedances of outer and inner cages of a double cage induction motors are (2+j1.2)O and (0.5+j3.5) O respectively. Determine the slip at which the 2 cages develop equal torques.
7. Why single phase induction motor is not self started? Discuss the different methods of starting a 1-phase Induction motor.

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8. A 230 V, 50Hz, 4-pole single-phase induction motor has the following equivalent circuit impedances:
   R_1m = 2.2ohm, X_1m = 3.1ohm, R₂' = 4.5ohm,
   X₂'=2.6ohm, X_M = 80 ohm
   Friction, windage and core loss=40W.
   For a slip of 0.03 pu, calculate:
   1. Input current

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   2. Power factor
9. Discuss the construction details of the following :
   1. Stepper Motors
   2. Universal Motors
   3. Shaded Pole type Induction Motor

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