Question 1:
The bedding on a cable consists of
A.
Hessian cloth
B.
Jute
C.
Any of the above
D.
None of the above
Answer: _________
Question 2:
The insulating material for a cable should have
A.
Low cost
B.
High dielectric strength
C.
High mechanical strength
D.
All of the above
Answer: _________
Question 3:
Underground cables are laid at sufficient depth
A.
To minimize temperature stresses
B.
To avoid being unearthed easily due to removal of soil
C.
To minimize the effect of shocks and vibrations due to gassing vehicles, etc.
D.
For all of the above reasons
Answer: _________
Question 4:
In capacitance grading a homogeneous dielectric is used.
A.
Yes
B.
No
Answer: _________
Question 5:
Dielectric strength of rubber is around
A.
5 kV/mm
B.
15 kV/mm
C.
30 kV/mm
D.
200 kV/mm
Answer: _________
Question 6:
The material for armouring on cable is usually
A.
Steel tape
B.
Galvanized steel wire
C.
Any of the above
D.
None of the above
Answer: _________
Question 7:
In the cables, sheaths are used to
A.
Prevent the moisture from entering the cable
B.
Provide enough strength
C.
Provide proper insulation
D.
None of the above
Answer: _________
Question 8:
In a cable immediately above metallic sheath ________ is provided.
A.
Earthing connection
B.
Bedding
C.
Armouring
D.
None of the above
Answer: _________
Question 9:
In capacitance grading of cables we use a _________ dielectric.
A.
Composite
B.
Porous
C.
Homogeneous
D.
Hygroscopic
Answer: _________
Question 10:
The insulating material for cables should
A.
Be acid proof
B.
Be non-inflammable
C.
Be non-hygroscopic
D.
Have all above properties
Answer: _________
Question 11:
In a cable the voltage stress is maximum at
A.
Sheath
B.
Insulator
C.
Surface of the conductor
D.
Core of the conductor
Answer: _________
Question 12:
The disadvantage with paper as insulating material is
A.
It is hygroscopic
B.
It has high capacitance
C.
It is an organic material
D.
None of the above
Answer: _________
Question 13:
Which of the following protects a cable against mechanical injury?
A.
Bedding
B.
Sheath
C.
Armouring
D.
None of the above
Answer: _________
Question 14:
In cables the charging current
A.
Lags the voltage by 90°
B.
Leads the voltage by 90°
C.
Lags the voltage by 180°
D.
Leads the voltage by 180°
Answer: _________
Question 15:
The relative permittivity of rubber is
A.
Between 2 and 3
B.
Between 5 and 6
C.
Between 8 and 10
D.
Between 12 and 14
Answer: _________
Question 16:
In the cables, the location of fault is usually found out by comparing
A.
The resistance of the conductor
B.
The inductance of conductors
C.
The capacitances of insulated conductors
D.
All above parameters
Answer: _________
Question 17:
In single core cables armouring is not done to
A.
Avoid excessive sheath losses
B.
Make it flexible
C.
Either of the above
D.
None of the above
Answer: _________
Question 18:
A cable carrying alternating current has
A.
Hysteresis losses only
B.
Hysteresis and leakage losses only
C.
Hysteresis, leakage and copper losses only
D.
Hysteresis, leakage, copper and friction losses
Answer: _________
Question 19:
In congested areas where excavation is expensive and inconvenient 'draw in system' of laying of underground cables is often adopted.
A.
Yes
B.
No
Answer: _________
Question 20:
The minimum dielectric stress in a cable is at
A.
Armour
B.
Bedding
C.
Conductor surface
D.
Lead sheath
Answer: _________
Question 21:
The breakdown voltage of a cable depends on
A.
Presence of moisture
B.
Working temperature
C.
Time of application of the voltage
D.
All of the above
Answer: _________
Question 22:
High tension cables are generally used up to
A.
11 kV
B.
33 kV
C.
66 kV
D.
132 kV
Answer: _________
Question 23:
Low tension cables are generally used up to
A.
200 V
B.
500 V
C.
700 V
D.
1000 V
Answer: _________
Question 24:
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
A.
One half
B.
Double
C.
Four times
D.
None of the above
Answer: _________
Question 25:
The breakdown of insulation of the cable can be avoided economically by the use of
A.
Inter-sheaths
B.
Insulating materials with different dielectric constants
C.
Both (A) and (B)
D.
None of the above
Answer: _________
Question 26:
In a cable, the maximum stress under operating conditions is at
A.
Insulation layer
B.
Sheath
C.
Armour
D.
Conductor surface
Answer: _________
Question 27:
Capacitance grading of cable implies
A.
Use of dielectrics of different permeabilities
B.
Grading according to capacitance of cables per km length
C.
Cables using single dielectric in different concentrations
D.
Capacitance required to be introduced at different lengths to counter the effect of inductance
Answer: _________
Question 28:
Pressure cables are generally not used beyond
A.
11 kV
B.
33 kV
C.
66 kV
D.
132 kV
Answer: _________
Question 29:
Solid type cables are considered unreliable beyond 66 kV because
A.
Insulation may melt due to higher temperature
B.
Skin effect dominates on the conductor
C.
Of corona loss between conductor and sheath material
D.
There is a danger of breakdown of insulation due to the presence of voids
Answer: _________
Question 30:
The insulation of the cable decreases with
A.
The increase in length of the insulation
B.
The decrease in the length of the insulation
C.
Either (A) or (B)
D.
None of the above
Answer: _________
Question 31:
The thickness of the layer of insulation on the conductor, in cables, depends upon
A.
Reactive power
B.
Power factor
C.
Voltage
D.
Current carrying capacity
Answer: _________
Question 32:
Polyethylene has very poor dielectric and ageing properties.
A.
Yes
B.
No
Answer: _________
Question 33:
The inters heaths in the cables are used to
A.
Minimize the stress
B.
Avoid the requirement of good insulation
C.
Provide proper stress distribution
D.
None of the above
Answer: _________
Question 34:
Conduit pipes are normally used to protect ________ cables.
A.
Unsheathed cables
B.
Armoured
C.
PVC sheathed cables
D.
All of the above
Answer: _________
Question 35:
_________ cables are used for 132 kV lines.
A.
High tension
B.
Super tension
C.
Extra high tension
D.
Extra super voltage
Answer: _________
Question 36:
Empire tape is
A.
Varnished cambric
B.
Vulcanized rubber
C.
Impregnated paper
D.
None of the above
Answer: _________
Question 37:
If a power cable and a communication cable are to run parallel the minimum distance between the two, to avoid interference, should be
A.
2 cm
B.
10 cm
C.
50 cm
D.
400 cm
Answer: _________
Question 38:
If a cable of homogeneous insulation has a maximum stress of 10 kV/mm, then the dielectric strength of insulation should be
A.
5 kV/mm
B.
10 kV/mm
C.
15 kV/mm
D.
30 kV/mm
Answer: _________
Question 39:
If the length of a cable is doubled, its capacitance
A.
Becomes one-fourth
B.
Becomes one-half
C.
Becomes double
D.
Remains unchanged
Answer: _________
Question 40:
Cables for 220 kV lines are invariably
A.
Mica insulated
B.
Paper insulated
C.
Compressed oil or compressed gas insulated
D.
Rubber insulated
Answer: _________
Question 41:
The metallic sheath may be made of lead or lead alloy or of aluminum.
A.
Yes
B.
No
Answer: _________
Question 42:
The insulating material should have
A.
Low permittivity
B.
High resistivity
C.
High dielectric strength
D.
All of the above
Answer: _________
Question 43:
The current carrying capacity of cables in D.C. is more than that in A.C. mainly due to
A.
Absence of harmonics
B.
Nonexistence of any stability limit
C.
Smaller dielectric loss
D.
Absence of ripples
Answer: _________
Question 44:
Which of the following insulation is used in cables?
A.
Varnished cambric
B.
Rubber
C.
Paper
D.
Any of the above
Answer: _________
Question 45:
It is difficult to maintain oil filled cables.
A.
Yes
B.
No
Answer: _________
Question 46:
Is a cable is to be designed for use on 1000 kV, which insulation would you prefer ?
A.
Polyvinyle chloride
B.
Vulcanised rubber
C.
Impregnated paper
D.
Compressed SFe gas
Answer: _________
Question 47:
The electrostatic stress in underground cables is
A.
Same at the conductor and the sheath
B.
Minimum at the conductor and maximum at the sheath
C.
Maximum at the conductor and minimum at the sheath
D.
Zero at the conductor as well as on the sheath
Answer: _________
Question 48:
Rubber is most commonly used insulation in cables.
A.
Yes
B.
No
Answer: _________
Question 49:
The advantage of oil filled cables is
A.
More perfect impregnation
B.
Smaller overall size
C.
No ionization, oxidation and formation of voids
D.
All of the above
Answer: _________
Question 50:
The thickness of metallic shielding on cables is usually
A.
0.04 mm
B.
0.2 to 0.4 mm
C.
3 to 5 mm
D.
40 to 60 mm
Answer: _________
Question 51:
Copper as conductor for cables is used as
A.
Annealed
B.
Hardened and tempered
C.
Hard drawn
D.
Alloy with chromium
Answer: _________
Question 52:
In case of three core flexible cable the color of the neutral is
A.
Blue
B.
Black
C.
Brown
D.
None of the above
Answer: _________
Question 53:
Natural rubber is obtained from milky sap of tropical trees.
A.
Yes
B.
No
Answer: _________
Question 54:
PVC stands for
A.
Polyvinyl chloride
B.
Post varnish conductor
C.
Pressed and varnished cloth
D.
Positive voltage conductor
Answer: _________
Question 55:
The advantage of cables over overhead transmission lines is
A.
Easy maintenance
B.
Low cost
C.
Can be used in congested areas
D.
Can be used in high voltage circuits
Answer: _________
Question 56:
Cables, generally used beyond 66 kV are
A.
Oil filled
B.
S.L. type
C.
Belted
D.
Armoured
Answer: _________
Question 57:
The surge resistance of cable is
A.
5 ohms
B.
20 ohms
C.
50 ohms
D.
100 ohms
Answer: _________
Answer Key
1:
C
2:
D
3:
C
4:
B
5:
C
6:
C
7:
A
8:
B
9:
A
10:
D
11:
C
Solution: In a cable, the voltage stress refers to the electrical stress experienced by the materials within the cable when it is subjected to an electric field. The voltage stress is maximum at the surface of the conductor. This is due to the phenomenon known as the skin effect . The skin effect causes the distribution of current within a conductor to be concentrated near the surface when the frequency of the electrical signal is high. As a result, the majority of the current flows through a thin layer near the surface of the conductor, leading to a higher voltage stress at the surface compared to the core. Therefore, Option C correctly identifies that the voltage stress is maximum at the surface of the conductor in a cable.
12:
A
13:
C
14:
B
15:
A
16:
C
17:
A
18:
B
19:
A
20:
D
21:
D
22:
A
23:
D
24:
A
25:
C
26:
D
27:
A
28:
C
29:
D
30:
A
31:
C
32:
B
33:
C
34:
A
35:
D
36:
A
37:
C
38:
B
39:
C
Solution: The correct answer is (C) Becomes double Here's why: Capacitance (C) of a cable is determined by the following factors: * The dielectric constant of the insulation material. * The area of the conductors. * The distance between the conductors (thickness of insulation). * The length of the cable. Think of a cable like a parallel plate capacitor. The formula for capacitance is roughly: C = (ε * A) / d Where: ε is the permittivity (related to the dielectric constant). A is the area of overlap of the conductors. d is the distance between the conductors. When the length of the cable is doubled, it's like increasing the area of overlap (A) between the conductors. Imagine connecting two identical capacitors in parallel. The total capacitance doubles. Therefore, if you double the length of the cable, you effectively double the capacitance .
40:
C
41:
B
42:
D
43:
C
44:
D
45:
A
46:
D
47:
C
48:
A
49:
D
50:
C
51:
A
52:
A
53:
A
54:
A
55:
C
56:
A
57:
C