JNTU III B.Tech Supplimentary Examinations, Aug/Sep 2008
UTILISATION OF ELECTRICAL ENERGY
(Electrical & Electronic Engineering)
1. (a) Though a.c. is superior to d.c. for electric drives, sometimes d.c. is preferred.
Give the reasons and mention some of the applications.
(b) A d.c. series motor drives a load, the torque of which varies as the square of the speed. The motor takes current of 30 amps, when the speed is 600 r.p.m. Determine the speed and current when the field winding is shunted by a diverter, the resistance of which is 1.5 times that of the field winding. The losses may be neglected.
2. (a) Draw and explain the output vs. time characteristics of any three types of loads.
(b) A motor has the following duty cycle:
Load rising from 200 to 400 h.p. — 4 minutes Uniform load 300 h.p. — 2 minutes Regenerative braking h.p. Returned to supply from 50 to zero —1 minute. Remains idle for 1 minute. Estimate the h.p. of the motor.
3. (a) Explain with a neat sketch the principle of coreless type induction furnace.
(b) 100Kg of tin is to be smelt in one hour in a smelting furnace. Determine the suitable rating of furnace if smelting temperature of tin is 2350C; specific heat is 0.055, latent heat of liquidification 13.3 Kcal/Kg. Take initial temperature of metal as 350C.
4. (a) Why electric traction is preferred to other types of traction?
(b) Explain the following electric braking methods.
ii. Rheostatic braking
iii. Regenerative braking.
(a) Lumen flux
(c) Luminance and
6. Write short notes on:
(a) Carbon arc lamp
(b) Flame arc lamp.
7. (a) Discuss relative merrits of
i. 1500 Volts D.C
ii. 25 KV
single phase 50 Hz rectifier locomotive system for the main line electrification of a railway in an industrial belt where a grid net work exists.
(b) Describe briefly with the help of neat sketch the single and double cater many over head line construction for railways.
8. (a) For a quadrilateral speed-time curve of an electric train, derive expression for the distance between stops and speed at the end of the coasting period.
(b) A train is required to run between stations 1.6kms apart at an average speed of 40km/hr. The run is to be made from a quadrilateral speed-time curve. The acceleration is 2km/hr/sec. The coasting and braking retardations are 0.16km/hr/sec and 3.2km/hr/sec respectively. Determine the duration of acceleration, coasting and braking and the distance covered in each period.