JNTU B.Tech Supplementary Examinations, Aug/Sep 2008
UTILISATION OF ELECTRICAL ENERGY
(Electrical & Electronic Engineering)
1. (a) Why and where is an individual drive recommended.
(b) The speed of a 15 h.p. (Metric) 400 V d.c. Shunt motor is to be reduced by 25% by the use of a controller. The field current is 2.5 amps and the armature resistance is 0.5 Ohm. Calculate the resistance of the controller, if the torque remains constant and the efficiency is 82%.
2. (a) Explain what you mean by Load Equalization and how it is accomplished.
(b) A motor fitted with a flywheel supplies a load torque of 150 Kg-m for 15 sec. During the no load period the flywheel regains its original speed. The motor torque is required to be limited to 85 Kg-m. Determine the moments of inertia of the flywheel. The no load speed of the motor is 500 r.p.m and it has a slip of 10% on full load.
3. (a) What are the factors to be considered for inductor design in induction heating?
(b) Give some applications of induction heating.
4. (a) What are various types of electric braking used?
(b) Explain how rheostatic braking is done in D.C. shunt motors and series motors.
5. (a) Discuss inverse square law & cosine law of Illumination.
(b) A lamp fitted with 120 degrees angled cone reflector illuminates circular area of 200 metres in diameter. The illumination of the disc increases uniformly from 0.5 metre-candle at the edge to 2 metre-candle at the centre. Determine
i. the total light received
ii. Average illumination of the disc
iii. Average c.p. of the source
6. Along the center of a line of a corridor, number of lamps are fitted with reflectors. The distance between the two adjacent lamps is 7.5cm and the height of each lamp from the floor is 5m. The candlepower of each lamp is 100 in all directions below the horizontal. Determine the maximum and minimum illumination along the centerline of the floor and draw a graph showing the variation of the illumination along this line between the two lamps.
7. Write a brief notes on the single phase a.c. series motor and comment upon it’s suitability for traction services. How is it performance compared with the d.c. series motor.
8. (a) Explain dead weight, accelerating weight and train resistance referred to traction.
(b) An electric train has an average speed between start to stop, Va = 40km/hr, acceleration 2.4km/hr/sec and retardation 4km/hr/sec, specific tractive resistance 55 newtons/tonne and average motor efficiency 75%. Estimate the average consumption of energy over a run of 800m, assuming trapezoidal speed time curve. Add 8% for the rotational inertia.