18.
31.
Disruptive critical voltage is
a.
a.
Equal to
b.
b.
Greater than
c.
c.
Less than
visual critical voltage for corona on an
overhead line.
Ans. c
19.
32.
Corona loss
a.
a.
Increases
b.
b.
Decreases
c.
c.
Does not change
the switching voltage on a transmission
line.
Ans. b
20.
33.
Handling of the telephone receiver may become dangerous due to
a.
a.
Electromagnetic induction
b.
b.
Electrostatic induction
c.
c.
Both electromagnetic and electrostatic induction
from a power line.
Ans. b
21.
34.
Mutual inductance between a three -phase power line and a telephone line due to third harmonic
current in the power line is
a.
a.
The algebraic sum of mutual inductances from individual phase wires
b.
b.
The arithmetic sum of mutual inductances from individual phase wires
c.
c.
Zero
Ans. b
22.
35.
Dielectric strength of mechanically sound porcelain is
a.
a.
10 kV/cm
b.
b.
22 kV/cm
c.
c.
65 kV/cm
d.
d.
100 kV/cm
Ans. c
23.
36.
Dielectric strength of glass is
a.
a.
22 kV/cm
b.
b.
60-66 kV/cm
c.
c.
140 kV/cm
d.
d.
240 kV/cm
Ans. c
24.
37.
Which one of the following statements is true?
a.
a.
For 11 kV insulators, the ratio of wet spark-over voltage to
working voltage is 8.3
b.
b.
For 66 kV insulators, the ratio of dry spark-over voltage to
working voltage is 8.3
c.
c.
For 11 kV insulators, the ratio of dry spark-over voltage to
working voltage is 8.3
Ans. c
25.
38.
Which one of the following statements is true?
a.
a.
Flash-over tests are performed on all insulators
b.
b.
Routine tests are performed on 1/2 percent of
insulators supplied
c.
c.
Design tests are done on 1/2 percent of
insulators supplied
Ans. none of the above
26.
39.
Which one of the following statements is true?
a.
a.
The spark-over voltage is less than the puncture voltage
b.
b.
The spark-over voltage is greater than the puncture voltage
c.
c.
The spark-over voltage is equal to the puncture voltage
Ans. a
27.
40.
Which one of the following statements is true?
The sheds of an insulator should be shaped
a.
a.
To conform to the electrostatic tube of force and the body should be shaped to
conform to the equipotential surfaces
b.
b.
To conform to the equipotential surfaces and the body should be shaped to
conform to the electrostatic tubes of force
c.
c.
To conform to the equipotential surfaces and so also the body
Ans. b
28.
41.
In a suspension insulator, the
mechanical stresses on the conductor are
a.
a.
Increased
b.
b.
Reduced
c.
c.
The same
Ans. b
29.
42.
The string efficiency of the insulator can be increased by
a.
a.
Increasing the number of strings in the insulator
b.
b.
Increasing the ratio , capacitance to earth/capacitance per insulator
c.
c.
By the correct grading of various capacitances
d.
d.
Decreasing the number of strings
Ans. c
30.
43.
String efficiency of insulators for wet flash-over is
a.
a.
Less
b.
b.
More
c.
c.
The same
as
that for dry flash-over
Ans. b
31.
44.
The potential across insulator discs can be equalized by having
a.
a.
The same capacitance for each unit
b.
b.
The highest capacitance for the lowest unit and decreasing progressively the
capacitance of other units
c.
c.
The lowest capacitance for the lowest unit and increasing progressively the
capacitance of other units
Ans. b
32.
45.
Grading ring serves the purpose of
a.
a.
Equalizing the voltage distribution across discs
b.
b.
An arcing shield
c.
c.
Both equalizing the voltage distribution and acting as an arcing shield
Ans. c
TRANSFORMERS -
1.
For a delta-star 3-phase
transformer the primary winding has N1 turns/phase and a secondary has N2 turns
/phase. The single-phase equivalent circuit will have a turns ratio
a.
N1/N2
b.
N1/ 3/N2
c.
N1/N2/ 3
Ans: (b)
- 2. The use of higher flux density in transformer design
a)
a)
reduces the transformer weight per kVA
b)
b)
increases the weight/kVA
c)
c)
increases the weight/kW
Ans. a
- 3. The conservator is used in a transformer because
a)
a)
it supplies oil to the transformer whenever needed
b)
b)
protects the transformer from damage
when oil expands due to rise in temperature
c)
c)
it provides fresh air and cools down the oil.
Ans. b
- 4. Which of the following has the highest efficiency?
a)
a)
dc shunt motor
b)
b)
transformer
c)
c)
induction motor
d)
d)
synchronous motor
Ans. b
D.C MOTOR Objective questions
- The speed of a d. c series motor at no load is
a)
a)
Zero
b)
b)
Infinity
c)
c)
1500 r. p. m
Ans. b
- A sinusoidal voltage of frequency 1 Hz is applied to the field of a d. c generator. The armature voltage will be
a)
a)
1 Hz square wave
b)
b) 1 Hz sin e wave
c)
c) d. c voltage
Ans. b
- The function of the commutator in a d. c machine is
a)
a)
to change ac to dc
b)
b) to change alternating voltage to direct
voltage
c)
c) for easy control of voltage
Ans. b
- The direction of rotation of a dc series motor can be reversed
a)
a)
by interchanging the supply terminals
b)
b)
by interchanging the field terminals
c)
c)
either a) or b).
Ans. b
- A dc shunt generator driven at normal speed in the normal direction fails to build up armature voltage because
a)
a)
the armature resistance is high
b)
b)
the field current is not sufficiently high
c)
c)
there is no residual magnetism.
Ans. c
- If a dc motor is connected across an ac supply , the dc motor will
a)
a)
burn as the eddy currents in the field produce heat
b)
b)
run at its normal speed
c)
c)
run at a lower speed
Ans. a
- What would happen if the field of dc shunt motors is opened?
a)
a)
the speed of the motor will be reduced
b)
b)
it will run at its normal speed
c)
c)
the speed will be enormously high , and the motor will destroy itself.
Ans. c
- Which one of the following motors is used in a locomotive?
a)
a)
Induction motor
b)
b)
dc series motor
c)
c)
Synchronous motor
Ans. b
9. The efficiency of a dc shunt generator has a maximum
value when
a)
a)
magnetic losses are equal to mechanical losses
b)
b) armature copper loss is equal to the constant
loss
c)
c) field copper loss is equal to the constant
loss.
Ans. b
10.
10. The
dummy coil in the dc machine is used to
d)
eliminate armature
reaction
e)
e)
bring about mechanical balance of
armature
f)
f)
eliminate reactance voltage
Ans. b
11. The sparking at the
brushes in a dc generator is attributed to
a) quick reversal of
current in the coil under commutation
b) armature reaction
c) reactance voltage
Ans. . c
12. Interpoles
in the armature of a dc
generator are used to
a)
a)
neutralize the reactance voltage
b)
b) neutralize the reactance voltage and the cross-magnetizing effect of the
armature reaction
c)
c)
neutralize the cross-magnetizing effect of the armature reaction
Ans. b
13. 13. The mechanical power develop by the dc motor is maximum when
a)
a)
back emf = applied voltage
b)
b)
back emf = 0
c)
c)
back emf = 0.5 times the applied
voltage.
Ans. c
14. 14. In series –parallel control method when
two dc series motors are connected
in series , the speed of the set is
(a)
(a)
half of the speed of he motors when
connected in parallel
(b)
(b) ¼ th of the speed of the motors when connected in parallel
(c)
(c)
same as in parallel.
Ans. b
15. 15. The armature torque of the
dc shunt motor is proportional to
a.
armature current onl
b.
field flux
c.
armature current and flux both
Ans. c
16. 16. The reversal of speed of motors used as electric braking is known as
a.
Regenerative
b.
Plugging
c.
Dynamic braking.
Ans. . b
17. 17. The method used for braking in rolling mills is
a.
i. plugging
b.
ii. regenerative braking
c.
iii. dynamic braking
Ans. a