Description : The insulating material for a cable should have (a) low cost (b) high dielectric strength (c) high mechanical strength (d) all of the above
Last Answer : (d) all of the above
Description : 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
Last Answer : (c) both (a) and (b)
Description : Dielectric (A) Is an electrical insulating material (B) Of low resistivity is preferred (C) Should have high thermal conductivity (D) Need not defy the corrosive action of chemicals
Last Answer : (A) Is an electrical insulating material
Description : The disadvantage with paper as insulating material is (a) it is hygroscopic (6) it has high capacitance (c) it is an organic material (d) none of the above
Last Answer : (a) it is hygroscopic
Description : 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 (a) 15 kV/mm (d) 30 kV/mm
Last Answer : (b) 10 kV/mm
Description : Dielectric strength of rubber is around (a) 5 kV/mm (b) 15 kV/mm (c) 30 kV/mm (d) 200 kV/mm
Last Answer : (c) 30 kV/mm
Description : The insulating material for cables should (a) be acid proof (b) be non-inflammable (c) be non-hygroscopic (d) have all above properties
Last Answer : (d) have all above properties
Description : 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 (6) double (c) four times (d) none of the above
Last Answer : (a) one half
Description : 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
Last Answer : (a) between 2 and 3
Description : Gold and silver are (A) dielectric materials (B) low resistivity conducting materials. (C) magnetic materials. (D) insulating materials.
Last Answer : (B) low resistivity conducting materials.
Description : Polyethylene has very poor dielectric and ageing properties. (a) Yes (b) No
Last Answer : (b) No
Description : In capacitance grading a homogeneous dielectric is used. (a) Yes (b) No
Description : 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 ... introduced at different lengths to counter the effect of inductance (e) none of the above
Last Answer : (a) use of dielectrics of different permeabilities
Description : In capacitance grading of cables we use a ______ dielectric. (a) composite (b) porous (c) homogeneous (d) hygroscopic
Last Answer : (a) composite
Description : The minimum dielectric stress in a cable is at (a) armour (b) bedding (c) conductor surface (d) lead sheath
Last Answer : (d) lead sheath
Description : The current carrying capacity of cables in D.C. is more that in A.C. mainly due to (a) absence of harmonics (b) non-existence of any stability limit (c) smaller dielectric loss (d) absence of ripples (e) none of the above
Last Answer : (c) smaller dielectric loss
Description : What is dielectric strength of an insulating material? What is its unit?
Last Answer : Dielectric Strength: The dielectric strength of an insulating material is the maximum voltage which the insulating medium can withstand without breakdown. Unit is volts per millimeter (V/mm), or kV/mm or kV/cm
Description : For an insulating material, dielectric strength and dielectric loss should be respectively (A) high and high (B) low and high (C) high and low (D) low and low.
Last Answer : For an insulating material, dielectric strength and dielectric loss should be respectively high and low
Description : In the cables, sheaths are used to (a) prevent the moisture from entering the cable (b) provide enough strength (e) provide proper insulation (d) none of the above
Last Answer : (a) prevent the moisture from entering the cable
Description : 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
Last Answer : (c) can be used in congested areas
Description : 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
Last Answer : (d) there is a danger of breakdown of insulation due to the presence of voids
Description : The material for armouring on cable is usually (a) steel tape (b) galvanised steel wire (c) any of the above (d) none of the above
Last Answer : (c) any of the above
Description : Low tension cables are generally used up to (a) 200 V (b) 500 V (c) 700 V (d) 1000 V
Last Answer : (d) 1000 V
Description : High tension cables are generally used up to (a) 11kV (b) 33kV (c) 66 kV (d) 132 kV
Last Answer : (a) 11kV
Description : cables are used for 132 kV lines. (a) High tension (b) Super tension (c) Extra high tension (d) Extra super voltage
Last Answer : (d) Extra super voltage
Description : Mica is a (A) Dielectric material. (B) Insulating material. (C) Magnetic material. (D) Both insulating and dielectric material.
Last Answer : (D) Both insulating and dielectric material.
Description : Define dielectric failure of electrical insulating material.
Last Answer : Definition of dielectric failure of electrical insulating material. In the insulating material if the applied voltage is increased gradually then for certain value insulation will break down, ... material vanishes its insulating properties and starts conducting, also known as dielectric failure.
Description : State failure phenomena observed in insulating material. State four reasons for failure of gaseous and solid dielectric materials.
Last Answer : Failure phenomena in insulating material means the dielectric property fails : The dielectric failure mean the dielectric strength of insulating material reduces due to high voltages or high ... 6. Due to poor maintenance of insulating material there may be possibility dielectric failure
Description : Zero permeability/permittivity implies which state? a) No ions are allowed in the medium b) No current is generated in the medium c) No magnetic or electric energy is permitted in the medium d) No resistivity
Last Answer : c) No magnetic or electric energy is permitted in the medium
Description : In free space, which of the following will be zero? a) Permittivity b) Permeability c) Conductivity d) Resistivity
Last Answer : c) Conductivity
Description : What is the type cable used in radiation areas?
Last Answer : Mineral insulated (MI) cables.
Description : Why bimetallic washers provided in aluminium copper transition joints?
Last Answer : To avoid galvanic corrosion failure.
Description : Why 1.1 kV grade cables used for 415V?
Last Answer : To take care of the both earthed / unearthed systems.
Description : What are the types of cables used in 6.6 kV and 415 V system voltages?
Last Answer : In 6.6 kV system AC (unearthed) grade having stranded aluminium conductors cables are used. Their insulation's are as follows. 1. XLPE - Crossed linked polyethylene insulation. 2. FRLS PVC - Fire ... V grade copper or aluminium stranded cables are used. Their insulations are HR PVC and FS type.
Description : How the required conductor size can be reduced by use of HRC fuses?
Last Answer : HRC fuse limits the peak amplitude of fault current. HRC fuse melts at prospective current but not allows circuit to pass their high rupturing capacity that is it’s kA.
Description : Why armouring done?
Last Answer : For mechanical strength, protect against damage by impact of an object.
Description : How armours /sheaths grounded?
Last Answer : 1 core cables -- sheaths/shields/armours grounded at one end only, other end insulated to prevent the circulating current through sheaths. 3 core cables -- grounded at both ends but not including core balance CT’s, since even small induced current causes 50N operation.
Description : What is the specified cable life?
Last Answer : 50 years.
Description : What are the advantages of XLPE?
Last Answer : a. Easy routing at heights b. Easy maintenance c. Large current (90 ºC) d. No sheath (no fatigue) e. No paper tape wrapping technique f. High dielectric strength g. Very little deformation ... i. Low tan delta and hence suits long routes j. Very light k. Good mechanical properties.
Description : What are the disadvantages of paper insulation?
Last Answer : a. Absorbs moisture. b. Cable termination/sealing problems.
Description : What are the purposes of cable trays?
Last Answer : a. Avoid sagging of cables b. Give mechanical support
Description : The metallic sheath may be made of lead or lead alloy or of aluminium. (a) Yes (b) No
Description : Rubber is most commonly used insulation in cables. (a) Yes (b) No
Last Answer : (a) Yes
Description : Natural rubber is obtained from milky sap of tropical trees. (a) Yes (b) No
Description : In congested areas where excavation is expensive and inconvenient 'draw in system' of laying of underground cables is often adopted. (a) Yes (b) No
Description : It is difficult to maintain oil filled cables. (a) Yes (b) No
Description : 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
Description : The advantage of oil filled cables is (a) more perfect impregnation (b) smaller overall size (c) no ionisation, oxidation and formation of voids (d) all of the above
Description : Copper as conductor for cables is used as (a) annealed (b) hardened and tempered (c) hard drawn (d) alloy with chromium
Last Answer : (a) annealed
Description : 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
Last Answer : (c) 50 cm