R09 - December, 2011 - Regular Examinations - Set - 1.

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 an expression for torque developed in the armature of DC motor.
(b) A 250V, DC shunt motor takes a line current of 20A resistance of shunt eld
winding is 200ohms and resistance of the armature is 0.3ohms. Find the
armature current and the back emf. [7 8]
2. (a) The voltage applied to a circuit is: v = 100 sin(wt 300), and the current


owing in the circuit is i = 15(wt 600). Determine the impedance, resistance,
reactance, power and the power factor of the circuit.
(b) A circuit consists of resistance R, and capacitive reactance of 30 
 connected
in series. Determine the value of R for which p.f. of the circuit is 0.8 and also
draw the phasor diagram. [8 7]
3. (a) State and explain Maximum Power Tranfer theorem.
(b) Calculate the value of load resistor RL to be connected across terminals A and
B which would draw the maximum power from the circuit and also nd the
maximum power( gure 4). [7 8]
Figure 4:
4. (a) Describe in detail constructional features of a single - phase, 50 Hz, core-type
transformer has a square cores of 20 cm side. Permissible maximum 
flux-
density is 1 wb/m. Calculate the number of turns per limb on the High and
low-voltage sides for a 3000/220 V ratio.
(b) Derive the induced e.m.f equation of transformer. [8 7]
5. Derive the relation between the torque and inductance of a moving iron instrument.
[15]
6. How the induction motors are classi ed? Explain the types of induction motors in
detail. [15]

7. (a) A transmission line cable consists of 19 strands of identical copper conductors
each 1.5 mm in diameter. The length of the cabe is 2 km but because of
the twist of the stands, the actual length of each conductor is increased by 5
percent. What is resistance of the cable? Take the resistivity of the copper
1.78 10??8 ohm-m.
(b) Explain KVL and KCL and ohm's Law. [10 5]
8. A separately excited generator running at 1500 rpm supplies 225A at 120V to a
current of constant resistance. What will current be when the speed is dropped to
1000 rpm with the eld current unaltered? The armature resistance is 0.06
 and
the total drop at the brushes is 1.5V. Ignore armature reaction. [15]
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