WorksheetsT&D Unit 4
Total questions: 30
Worksheet time: 36mins
Which of the following is not an advantage of power transfer through underground cables?
Less chance of faults
Low capital cost
Low maintenance cost
Less chances of damage due to storms and lightning
WHich of the following is not a component of a cable?
Cores
Insulation
Counterpoise
Metallic sheath
Cables are armoured to
protect cable from mechanical injury during laying
protect cable from mechanical injury during handling
Both options 1 and 2
None of the above
Which of the following is not a required property of insulating cables?
High insulating resistance
Highly Hygroscopic
High mechanical strength
High dielectric strength
Which of the following is not an insulating material for cables?
SF6
Poly vinyl chloride
varnished cambric
Vulcanised india rubber
Which of the following is not a cable used for 3 phase systems?
Belted cable
Screened cable
Flexible cable
Pressure cable
Which of the following is not a method for laying underground cables?
Scatter laying
Direct laying
Draw-in laying
Solid laying
Insulation resistance of a cable does not depend on
Resistivity of the insulating material
Distance between cables
Length of the cable
Radius of core
The capacitance of a cable per metere length does not depend on
Conductor diameter
Sheath diameter
Permittivity of air
Permittivity of insulating material
Grading of cables refers to
Classifying of cables depending on the matyerial
Evaluating the quality of cables
Achieving uniform magnetic field in a cable
Achieving uniform electrostatic stress in a cable
WHich of the following is a method of grading of cables?
Intersheath grading
Capacitance grading
Both option 1 and 2
None of the above
In capacitance grading, a composite dielectric is used which consists of various layers of different dielectrics in such a manner that relative permittivity of any layer is
constant
varies inversely with distance from centre
varies directly with distance from centre
None of the above
Intersheath grading of cables uses
homogeneous dielectric
composite dielectric
no dielectric
hybrid combination
Capacitance of a cable system is more than an overhead system since
they are underground
conductors are nearer to each other and to the earthed sheath
they are operated at lesser voltage
None of the above
Which of the following is not a loss present in cables
Rotational loss
Copper loss
Hysterisis loss in the dielectric
Eddy current loss in the sheath
Which of the following is not a type of cable fault?
Open circuit
Over voltage
Short circuit
Earth fault
What are the methods for locating faults in underground cables?
Varley loop test
Murray loop test
Miller loop test
Options 1 and 2
Options 2 and 3
Variation of dielectric power factor with temperature?
Remain constant
Keeps decreasing
Increases till a point and then decreases
Decreases till a point and then increases
The leakage resistance of a 50km long cable is 1Megohm .
For a 100km long cable, it will be
1Megohm
2 Megohms
0.66 Megohms
None of the above
Sheaths are used in cables to
provide proper insulation
provide mechanical strength
prevent ingress of moisture
None of the above
Three insulating materials with same maximum working stress and permittivities 2.5,.3.0 and 4.0 are used in a single core cable. The location of the material with respect to the core of the cable is
2.5,.3.0 and 4.0
3.0, 2.5 and 4.0
4.0, 3.0, 2.5
4.0, 2.5, 3.0
Three insulating materialsnwith breakdown strengths 0f 250kv/cm, 200kv/cm, 150kv/cm and permittivities of 2.5, 3.0 and 3.5 are used in a single core cable. If the factor of safety for the materials is 5, the location of the materials with respect to the core of the cable will be
2.5, 3.0 and 3.5
3.0, 2.5, 3.5
3.5, 3.0, 2.5
3.5, 2.5, 3.0
The insulation resistance of a cable of length 10km is 1Megohm. Its resistance for 50km length will be
1 Megohm
5 Megohms
0.2 Megohm
None of the above
The capacitance of a 3 core cable between any two conductors with sheath earthed is 2uF. The capacitance per phase will be
1 uF
4 uF
0.667 uF
1.414 uF
If delta is the loss angle of the cable, its power factor is
Sin (delta)
Cos (delta)
Powerfactor is independent of delta
None of the above
In a 3 core cable, the capacitance between two conductors is 3 μF. What will be the capacitance per phase?
1.5 μF
3 μF
6 μF
12 μF
The capacitances of a 3 phase belted cable are 12.6 μ F between the three cores bunched together and the lead sheath and 7.4 μ F between one core and the other two connected to sheath. What will be the charging current drawn by the cable when connected to a 66 kV supply?
100 A
99.3648 A
105.236 A
107.74 A
Why is the single core cables not provided with armouring?
Avoids excessive loss in the armour.
Make the cable more flexible
Make the cable non hygroscopic
None of the above
Which among the following cables are generally suited for the voltages upto 11 kV?
Belted cables
Screened cables
Pressure cables
None of these
The charging current drawn by the cable
Lags behind the voltage by 90°.
Leads the voltage by 90°.
Are in phase with each other
Leads the voltage by 60°
