R09 - December, 2011 - Regular Examinations - Set - 3.

II B.Tech I Semester Examinations,December 2011
BASIC ELECTRICAL ENGINEERING
Common to Information Technology, Computer Science And Engineering
Time: 3 hours Max Marks: 75
Answer any FIVE Questions
All Questions carry equal marks
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1. (a) Derive the induced e.m.f equation of transformer.
(b) A single-phase, 25 Hz transformer has 50 primary turns and 600 secondary
turns. The cross sectional area of the core is 400 sq.cm. If the primary of the
transformer is connected to 230 V supply. Find
i. the secondary induced emf
ii. the 
flux density (peak) in the core. [7 8]
2. (a) What are the applications of DC generators?
(b) The resistance of the eld circuit of a shunt excited d.c generator is 200
 when
the output of the generator is 120 kW, the terminal voltage is 525V and the
generated e.m.f is 550V. Calculate
i. the armature resistance and
ii. if the terminal voltage is 540 V at 80 kW of the output what will be the
generated emf? [5 10]
3. An a.c. circuit consists of a resistance of 5 ohms, an inductance of 0.1 H, and a
capacitance of 100 F, all in series. Determine for this circuit:
(a) total reactance;
(b) impedance;
(c) admittance;
(d) susceptance, and
(e) conductance.
The supply frequency is 60 Hz. [15]
4. (a) Explain why a 3-phase induction motor can not develop torque when running
at synchronous speed.
(b) A 3-phase, 4-pole 50Hz induction motor has a slip of 1% at no-load and 3%
at full load. Find
i. Synchronous speed
ii. Full-load speed
iii. No-load speed. [7 8]
5. A 230 V dc shunt motor having an armature resistance of 0.3
 takes 3A excluding
a eld current of 1A when running on no-load. Determine its e ciency taking
currents as 30A. [15]

6. Explain the essential requirements of indicating instruments with necessary dia-
grams. [15]
7. Find the current through 50
 resistor, using Nortan's theorem in the unbalanced
wheatstone bridge shown below in gure 5. [15]
Figure 5:
8. An aluminum wire 10 meters long and 2 mm in diameter is connected in parallel
with a copper wire 6 meters long. A total current of 2 A is passed through the
combination and it is found that current through the aluminum wire is 1.25 A .
Calculate the diameter of copper wire. Speci c resistance of copper is 1.6 10??6
ohm-cm and that of aluminum is 2.6 10??6 ohm-cm. [15]
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