JNTU Previous Papers-B Tech-Utilization of Electrical Energy-Aug/Sep-2008

JNTU Previous Papers-B Tech-Utilization of Electrical Energy-Aug/Sep-2008

 Supplementary Examinations

UTILIZATION OF ELECTRICAL ENERGY

(Electrical & Electronic Engineering)

SET-I

 

1. (a) Compare and contrast the slip ring and squirrel cage induction motors from

the application point of view.

(b) A series motor working on 500 V d.c supply runs at a speed of 1000 r.p.m. When The load current is 120 amps. The resistance of the motor 0.15 Ohm, of which 0.04 Ohm is the resistance of the field. Calculate the speed of the motor when the torque is half of the full load torque and the field winding is connected in parallel with a diverter of resistance 0.08 Ohm, assuming an unsaturated magnetic circuit.

 

2. (a) Derive an expression for the temperature rise of an equipment in terms of the heating time constant.

(b) At full load of 10 h.p., the temperature rise of a motor is 25 degrees C after one hour, and 40 degrees C after 2 hours. Find the final temperature rise on full load. Assume that the iron losses are 80% of full load copper losses.

 

3. (a) Explain the principle of Induction heating, What are the applications of induction heating?

(b) With a neat sketch explain the working principle of coreless type induction furnace.

 

4. (a) What are the advantages of electric braking over mechanical braking.

(b) Explain regenerating braking of traction motors?

 

5. (a) State and Explain cos3; law.

(b) A lamp of 500 candle power is placed at the centre of a room, 20m×10m×5m. Calculate the illumination in each corner of the floor and a point in the middle of a 10m wall at a height of 2m from floor.

 

6. (a) Discuss about flood lighting in detail.

(b) A drawing hall 30m× 13m with a ceiling height of 5m is to be provided with a general illumination of 120 lux. Taking a coefficient of utilization of 0.5 and depreciation factor of 1.4, determine the number of fluorescent tubes required, their spacing mounting height and total wattage. Taking luminous efficiency of fluorescent tube as 40 lumens/watt for 80watt tube.

 

7. (a) Discuss the merits and demerits of the D.C and 1 – ? A.C systems for the

main and suburban line electrification of the railways.

(b) Which system you consider to be the best for the suburban railways in the vicinity of large cities? Give reasons for your answer.

 

8. (a) Define specific energy output and specific energy consumption.

(b) An electric locomotive of 100 tonnes can just accelerate a train of 500 tonnes (trailing weight) with an acceleration of 1km/hr/sec on an up gradient 1 in 1000. Tractive resistance of the track is 45 newtons/tonne and the rotational inertia is 10%. If this locomotive is helped by another locomotive of 120 tonnes, find

i. the trailing weight that can be hauled up the same gradient, under the same condition

ii. the maximum gradient, the trailing hauled load remaining unchanged. Assume adhesive weight expressed as percentage of total dead weight to be same for both the locomotives.

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