I B.Tech - Regular Examinations, June 2009
First Year
BASIC ELECTRICAL ENGINEERING- SET NO: 4
(Regulation 2007)
Time : 3 hours |
Maximam Marks:80 |
Answer any FIVE Questions
1. Find the current through and the voltage across all the elements by using kirchoffs
laws as shown in figure 1.
2.(a) Using star delta transformation find the current and power supplied by the
battery as shown in figure 2a.
(b) Describe in detail the steps to apply superposition theorem.
3.(a) Prove
(b) A primary coil having an inductance of 100 µH is connected in series with
a secondary coil of 240 µH and the total inductance of the combination is
measured as 146 µH. Determine the coefficient of coupling.
4.(a) A coil of power factor 0.9 is in series with a 120 µF capacitor. When connected
to a 50 Hz supply, the potential difference across the coil is equal to the potential difference across the capacitor. Find the resistance and inductanceof the coil.
(b) A metal filament lamp rated 750 W, 110V is to be connected in series with a
capacitor across a 220V, 50Hz supply. Calculate
i. The capacitance required
ii. The power factor.
5.(a) A double wound, single phase transformer is required to step down from 1900
V to 240 V, 50 Hz. It is to have 1.5V per turn. Calculate the required number
of turns on the Primary and Secondary windings respectively. The peak value
of flux density is required to be not more than 1.2 wb/sq.cm. Calculate the
required cross-sectional area of the steel core. If the output is 10KVA, calculate
secondary current. (b) A 2200/200V, single phase transformer takes 1A at the high voltage side on
no-load at a power factor of 0.385 lagging. Calculate the iron losses if a load of
50 A at a power of 0.8 lagging is taken from the secondary of the transformer.
Calculate the actual primary current and its power factor.
6.(a) Compare the operating characteristics of different types of DC motors.
(b) Draw the speed load characteristics curve of the DC shunt and series motor.
Use these curves to explain the applications for which these motors are used.
7.A 4-pole, 50 Hz, three phase, induction motor develops a maximum torque of 95
N-m at 1200 r.p.m. The resistance of the star-connected rotor is 0.5
/phase.
Caculate the value of resistance that must be inserted in series with each rotor
phase to produce a starting torque equal to 3/4 the maximum torque.
8.(a) Why is the scale of a MI instrument non uniform? Explain.
(b) With neat sketch, explain the process of eddy current damping.
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