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Name : ……………………………………………………………
Roll No. : ……………………………………………..…………..
Invigilator’s Signature : ………………………………………..
CS/B.Tech (OLD)/SEM-2/EE-201/2013
2013
BASIC ELECTRICAL ENGINEERING
Time Allotted : 3 Hours Full Marks : 70

The figures in the margin indicate full marks.

Candidates are required to give their answers in their own words
as far as practicable.

GROUP – A
( Multiple Choice Type Questions )

1. Choose the correct alternatives for any ten of the

following : 10 × 1 = 10
i) In three-phase induction motor
a) 3-phase supply is to be given to the stator winding
and d.c. supply the rotor winding
b) only 3-phase supply is to be given to the stator
winding
c) 3-phase supply is to be given to both stator and
rotor winding
d) 3-phase supply is to be given to rotor winding.
ii) A 400 V, 50 Hz three-phase induction motor rotates at
1440 rpm on full-load. The motor is wounded for
a) 2 poles b) 4 poles
c) 6 poles d) 8 poles.

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iii) The slip of 400 V, 3-phase, 4-pole induction motor when

rotating at 1440 rpm is

a) 2% b) 3%

c) 4% d) 5%.

iv) A sinusoidal voltage is represented as

& %)
" = 141# 4 sin ( 314·18 t $ +. Its rms value of voltages,
' 2*
frequency and phase angle are respectively

a) 141·42 V, 314·16 Hz, 90°

!
b) 100 V, 100 Hz, – 90°

c) 87·92 V, 56 Hz, 90°

d) 200 V, 50 Hz, – 90°.

v) The direction of current in an a.c. circuit is

a) always in one direction

b) varying from time to time

c) unpredictable

d) from positive to negative.

vi) In a three-phase star connected system, the relation

between the phase and the line voltage is
a) V p = VL b) Vp = 3 VL

c) V p = VL / 3 d) V p = V L / 3.

vii)
! When a pure inductance ! is connected to an a.c. source,
the voltage .................... the current through it by
! !
.................... .

a) lags, 90° b) leads, 90°

c) lags, 45° d) leads, 45°.

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viii) The power consumed by a pure capacitance connected

to a.c. source is
a) zero b) very low
c) high d) infinite.
ix) In a series RL circuit the phase difference between the
applied a.c. voltage and current increases when
a) R is increased
b) X L is increased
c) X L is decreased
d) supply frequency is increased.
!
x) When a phasor is multiplied by j and – j, it is rotated
! through .................... in the anticlockwise direction
respectively by
a) 90°, 270° b) 90°, 90°
c) 90°, 180° d) 270°, 90°.
xi) An a.c. voltage of ( 100 + j 60 ) V is applied to a circuit
to give a current of ( – 4 + j 10 ) A. The power dissipated
by the current is
a) – 100 W b) 100 W
c) 200 W d) 400 W.
xii) In a parallel a.c. circuit, if the supply frequency is
greater than the resonant frequency, then the circuit is
a) inductive b) resistive
c) capacitive d) none of these.
xiii) Q factor of a series circuit consisting R = 10 ohms,
L = 0·1 H and C = 10 µF is
a) 115 b) 100
c) 10 d) 1.
xiv) If a parallel circuit is shunted by a resistance then the
a) Q factor is increased
b) impedance is decreased
c) both (a) & (b)
d) none of these.

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GROUP – B
( Short Answer Type Questions )
Answer any three of the following. 3 × 5 = 15

2. A 220 volts separately excited DC machine has an armature

resistance of 0·4 Ω. If the load current is 20 ampere, find the

induced emf when the machine operates

i) as a motor

ii) as a generator.

3. A 415 V / 220 V transformer takes a no-load current of 1 A

and operates at a power factor of 0·19 lagging when the

secondary supplies a current of 100 A at 0·8 p.f. lagging.

Find the primary current.

4. A 6-pole, lap connected D.C. generator with 125 coils

generates a voltage of 400 volts on open circuit when

running at 1200 rpm. Find the useful flux per pole. For the
same value of the flux per pole, find the voltage at open

circuit when the machine runs at 1000 rpm.

5. Describe the Open Circuit Characteristics ( OCC ) of a D.C.

generator.

6. Explain the method of measurement of balanced three

phases power by two wattmeter method under different
power factor conditions.

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7. A 3-phase, 6-pole, 50 Hz induction motor has a slip of 1% at

no load and 3% at full load. Calculate

i) synchronous speed

ii) no load speed

iii) full load speed

iv) frequency of rotor current at standstill

v) frequency rotor current at full load.

GROUP – C
( Long Answer Type Questions )
Answer any three of the following. 3 × 15 = 45

8. a) Explain the method of measurement of balanced

3-phage power by 2-wattmeter method. Draw the neat

circuit diagram. 7

b) Three equal impedances ( 6 + j 8 ) Ω are connected in

across a 400 V, 3-phase and 50 Hz supply. Calculate

i) the line current and the phase current

ii) the power factor

iii) active and reactive powers drawn by the load per

phase. 8

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9. a) An a.c. series circuit consisting of a pure resistance of

25 Ω, inductance of 0·15 H and capacitance of 80 µF is
supplied from a 230 V, 50 Hz a.c. Find

i) the impedance of the circuit

ii) the current

iii) the power drawn by the circuit

iv) the power factor.

b) Draw the phasor diagram. 10 + 5

10. a) Write short notes on the following :

i) Active & ractive power

ii) Power factor

iii) Apparent power.

b) The equation of an alternating current is

i = 62·35 sin 323 t A. Determine its

i) maximum value

ii) frequency

iii) rms value

iv) average value

v) form factor.

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11. a) Explain why power loss in a pure inductance / pure

capacitance is equal to zero in an a.c. circuit. 5

b) A coil of resistance 2 ohms and inductance 0·01 H is

connected in series with a capacitor across 200 V

mains. What must be the capacitance for maximum

current at 25 Hz ? Find also the current and voltage in

the capacitor. 10

12. a) State and prove Thevenin’s theorem. 5

b) Find the currents through R BC , R CD , R BD in the

following circuit. 5

c) Explain with reasons as to why transformer core is

made up of silicon steel lamination. 5

13. a) Draw the phasor diagram of single phase transformer

for lagging power factor load. 5

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b) The open circuit and short circuit test-data of a 5 kVA,

200/400 volts, 50 Hz, single phase transformers are :

i) O.C. test : primary voltage = 200 volts, I = 0·75 A,

W = 75 W

ii) S.C. test : primary voltage = 18 volts, S.C. current

on the secondary side = 12·5 A, W = 60 W.

Find the parameters of the equivalent circuits. 5

c) State and explain Faraday’s law of electromagnetism. 5

14. a) Give the speed control methods of 3-phase induction

motor. 6

b) A 4-pole, 3-phase, 275 kW, 440 V, 50 Hz, induction

motor has a speed of 1460 rpm on full-load. Calculate
the slip and speed of the rotating magnetic field. 9

15. Write short notes on the following : 5×3

a) Eddy current losses

b) Hysteresis loss

c) Dielectric constant ( K )

d) Principle of operation of 3-phase induction motor.

e) Quality factor.

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