I B.Tech - Regular Examinations, June 2009
First Year
BASIC ELECTRICAL ENGINEERING- SET NO: 1
(Regulation 2007)
Time : 3 hours |
Maximam Marks:80 |
Answer any FIVE Questions
1. (a) Six resistors are connected as shown in figure 1a. If a battery having an emf
of 30V and an internal resistance of 2
is connected to terminals A and B.
Find
i. current from battery
ii. potential difference across 10
and 12
.
Find the effective resistance of the following combination of resistances and
the voltage drop across each resistance when the applied voltage is 70V across
P and Q as shown in figure 1b.
2.Find the voltage across AB by using superposition theorem as shown in figure 2.
3.(a) A coil of 500 turns is wound on a wooden former and a current of 7A produces
a magnetic flux of 30mWb. Calculate the inductance of the coil and induced
emf when the current is reversed in 0.01sec.
(b) The no of turns in a coil is 300. When a current of 4A flows in this coil the flux
in the coil is 0.06mWb. When this current is reduced to 0 in 4ms the voltage
induced in a coil lying in the vicinity of the coil is 70V. If the coefficient of
coupling between the coil is 0.9, find self inductance of the two coils, mutual
inductance and no of turns in the second coil.
4.Explain the behaviour of AC through
(a) Pure
(b) Pure
(c) Pure C circuits
For each case, derive the instantaneous value of V and I, Impedance, Average power,
Power factor, Instantaneous power and the relevant phasors.
5.Calculate the efficiency at full load, half load and 1/4 th load at
(a) unity power factor
(b) 0.71 power factor lagging for a 80KVA ,1100/250V , 50Hz , 1 phase transformer
whose losses are as follows.: iron loss = 800W, total copper losses with 160A
in the low voltage winding is 200W.
6.(a) What is the function of a commutator in a DC machine? Discuss with relevant
figures.
(b) Differentiate between slip rings and commutator.
(c) A 4 pole wave wound DC generator has 50 slots and 24 conductors per slot.
The flux per pole is 10 mWb. Determine the induced emf in the armature if
it is rotating at a speed of 700rpm.
7.(a) Give the difference between an induction motor and a transformer.
(b) A 12 pole, 3 phase alternator driven at 500 rpm supplies power to a 8 pole 3
phase induction motor. If slip of motor at full load is 3%, calculate the speed
of the motor.
(c) A 3 phase induction motor has starting torque of 100% and a maximum torque
of 200% of the full load torque. Find slip at maximum torque.
8.Discuss the necessity of damping torque in indicating instrument. Explain with
neat sketch the different methods of producing them.
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