List Of Objective Questions On Cables
1.The thickness of the layer of insulation on the conductor, in cables, depends upon
reactive power
power factor
voltage
current carrying capacity
ANSWER : : voltage
2.Which of the following protects a cable against mechanical injury ?
Bedding
Sheath
Armouring
None of the above
ANSWER : : Armouring
3.Which of the following insulation is used in cables ?
Varnished cambric
Rubber
Paper
Any of the above
ANSWER : : Any of the above
4.PVC stands for
polyvinyl chloride
post varnish conductor
pressed and varnished cloth
positive voltage conductor
ANSWER : : polyvinyl chloride
5.In a cable, the maximum stress under operating conditions is at
insulation layer
sheath
armour
conductor surface
ANSWER : : conductor surface
6.Cables, generally used beyond 66 kV are
oil filled
S.L. type
belted
armoured
ANSWER : : oil filled
7.The surge resistance of cable is
5 ohms
20 ohms
50 ohms
100 ohms
ANSWER : : 50 ohms
8.The current carrying capacity of cables in D.C. is more thanthat in A.C. mainly due to
absence of harmonics
non-existence of any stability limit
smaller dielectric loss
absence of ripples
ANSWER : : smaller dielectric loss
9.Pressure cables are generally not used beyond
11 kV
33 kV
66 kV
132 kV
ANSWER : : 66 kV
10.The minimum dielectric stress in a cable is at
armour
bedding
conductor surface
lead sheath
ANSWER : : lead sheath
11.Conduit pipes are normally used to protect _____ cables.
unsheathed cables
armoured
PVC sheathed cables
all of the above
ANSWER : : unsheathed cables
12.Dielectric strength of rubber is around
5 kV/mm
15 kV/mm
30 kV/mm
200 kV/mm
ANSWER : : 30 kV/mm
13.In a cable immediately above metallic sheath _____ is provided.
earthing connection
bedding
armouring
none of the above
ANSWER : : bedding
14.In case of three core flexible cable the colour of the neutral is
blue
black
brown
none of the above
ANSWER : : blue
15.High tension cables are generally used upto
11kV
33kV
66 kV
132 kV
ANSWER : : 11kV
16.In single core cables armouring is not done to
avoid excessive sheath losses
make it flexible
either of the above
none of the above
ANSWER : : avoid excessive sheath losses
17.The bedding on a cable consists of
hessian cloth
jute
any of the above
none of the above
ANSWER : : any of the above
18.The insulating material for cables should
be acid proof
be non-inflammable
be non-hygroscopic
have all above properties
ANSWER : : have all above properties
19.Empire tape is
varnished cambric
vulcanised rubber
impregnated paper
none of the above
ANSWER : : varnished cambric
20.The material for armouring on cable is usually
steel tape
galvanised steel wire
any of the above
none of the above
ANSWER : : any of the above
21.In capacitance grading of cables we use a ______ dielectric.
composite
porous
homogeneous
hygroscopic
ANSWER : : composite
22.Low tension cables are generally used upto
200 V
500 V
700 V
1000 V
ANSWER : : 1000 V
23.The breakdown voltage of a cable depends on
presence of moisture
working temperature
time of application of the voltage
all of the above
ANSWER : : all of the above
24.Is a cable is to be designed for use on 1000 kV, which insulation would you prefer ?
Polyvinyle chloride
Vulcanised rubber
Impregnated paper
Compressed SFe gas
ANSWER : : Compressed SFe gas
25.In cables the charging current
lags the voltage by 90�
leads the voltage by 90�
lags the voltage by 180�
leads the voltage by 180�
ANSWER : : leads the voltage by 90�
26.The thickness of metallic shielding on cables is usually
0.04 mm
0.2 to 0.4 mm
3 to 5 mm
40 to 60 mm
ANSWER : : 0.04 mm
27.Underground cables are laid at sufficient depth
to minimise temperature stresses
to avoid being unearthed easily due to removal of soil
to minimise the effect of shocks and vibrations due to gassing vehicles, etc.
for all of the above reasons
ANSWER : : to minimise the effect of shocks and vibrations due to gassing vehicles, etc.
28.If a cable of homogeneous insulation has a maximum stress of 10 kV/mm, then the dielectric strength of insulation should be
5 kV/mm
10 kV/mm
15 kV/mm
30 kV/mm
ANSWER : : 10 kV/mm
29.The insulation of the cable decreases with
the increase in length of the insulation
the decrease in the length of the insulation
either (a) or (b)
none of the above
ANSWER : : the increase in length of the insulation
30.The disadvantage with paper as insulating material is
it is hygroscopic
it has high capacitance
it is an organic material
none of the above
ANSWER : : it is hygroscopic
31.In the cables, sheaths are used to
prevent the moisture from entering the cable
provide enough strength
provide proper insulation
none of the above
ANSWER : : prevent the moisture from entering the cable
32.The breakdown of insulation of the cable can be avoided economically by the use of
inter-sheaths
insulating materials with different dielectric constants
both (a) and (b)
none of the above
ANSWER : : both (a) and (b)
33.If the length of a cable is doubled, its capacitance
becomes one-fourth
becomes one-half
becomes double
remains unchanged
ANSWER : : becomes double
34.Cables for 220 kV lines are invariably
mica insulated
paper insulated
compressed oil or compressed gas insulated
rubber insulated
ANSWER : : compressed oil or compressed gas insulated
35.A cable carrying alternating current has
hysteresis losses only
hysteresis and leakage losses only
hysteresis, leakage and copper losses only
hysteresis, leakage, copper and friction losses
ANSWER : : hysteresis and leakage losses only
36.A certain cable has an insulation of relative permittivity 4. If the insulation is replaced by one of relative permittivity 2, the capacitance of the cable will become
one half
double
four times
none of the above
ANSWER : : one half
37.The advantage of oil filled cables is
more perfect impregnation
smaller overall size
no ionisation, oxidation and formation of voids
all of the above
ANSWER : : all of the above
38.If a power cable and a communication cable are to run parallel the minimum distance between the two, to avoid interference, should be
2 cm
10 cm
50 cm
400 cm
ANSWER : : 50 cm
39.The advantage of cables over overhead transmission lines is
easy maintenance
low cost
can be used in congested areas
can be used in high voltage circuits
ANSWER : : can be used in congested areas
40.The insulating material should have
low permittivity
high resistivity
high dielectric strength
all of the above
ANSWER : : all of the above
41.Solid type cables are considered unreliable beyond 66 kV because
insulation may melt due to higher temperature
skin effect dominates on the conduc�tor
of corona loss between conductor and sheath material
there is a danger of breakdown of insulation due to the presence of voids
ANSWER : : there is a danger of breakdown of insulation due to the presence of voids
42.In a cable the voltage stress is maximum at
sheath
insulator
surface of the conductor
core of the conductor
ANSWER : : core of the conductor
43.The electrostatic stress in underground cables is
same at the conductor and the sheath
minimum at the conductor and maximum at the sheath
maximum at the conductor and minimum at the sheath
zero at the conductor as well as on the sheath
ANSWER : : maximum at the conductor and minimum at the sheath
44.The intersheaths in the cables are used to
minimize the stress
avoid the requirement of good insulation
provide proper stress distribution
none of the above
ANSWER : : provide proper stress distribution
45.Copper as conductor for cables is used as
annealed
hardened and tempered
hard drawn
alloy with chromium
ANSWER : : annealed
46.Capacitance grading of cable implies
use of dielectrics of different permeabilities
grading according to capacitance of cables per km length
cables using single dielectric in different concentrations
capacitance required to be introduced at different lengths to counter the effect of inductance
ANSWER : : use of dielectrics of different permeabilities
47.Natural rubber is obtained from milky sap of tropical trees.
Yes
No
Yes
Rubber is most commonly used insulation in cables.
ANSWER : 1 Yes
48.In capacitance grading a homogeneous dielectric is used.
Yes
No
No
In congested areas where excavation is expensive and inconvenient ‘draw in system’ of laying of underground cables
ANSWER : often adopted.
49.Polyethylene has very poor dielectric and ageing properties.
Yes
No
No
metallic sheath may be made of lead or lead alloy or of aluminium.
ANSWER : 1 Yes