Description : If the length of a cable is doubled, its capacitance (a) becomes one-fourth (b) becomes one-half (c) becomes double (d) remains unchanged
Last Answer : (c) becomes double
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 : A cylindrical cable of core radius 1.25cm and impregnated paper insulation of thickness 2.13cm and relative permittivity 3.5. Compute the capacitance of the cable/km (in nF
Last Answer : To calculate the capacitance of the cable per kilometer, you can use the following formula: C = ε * ε0 * A / d where: C is the capacitance of the cable per kilometer (in farads) ε is ... * 10^9 = 644 nF/km So the capacitance of the cable per kilometer would be approximately 644 nanofarads.
Description : A cable of core radius 1.25cm and impregnated paper insulation of thickness 2.13cm and relative permittivity 3.5. Compute the capacitance of the cable/km(in nF) a) 195.7 b) 179.5 c) 157.9 d) 197.5
Last Answer : a) 195.7
Description : A cable has an insulation of relative permittivity 2. If the insulation is replaced by one of relative permittivity 4, then capacitance of the cable (a) is doubled (b) is halved (c) remains unchanged (d) is reduced
Last Answer : B
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 : 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 (e) none of the above
Last Answer : (d) Compressed SFe gas
Description : 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
Last Answer : (a) the increase in length of the insulation
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 : 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 : 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 : In a cable, the maximum stress under operating conditions is at (a) insulation layer (b) sheath (c) armour (d) conductor surface
Last Answer : (d) conductor surface
Description : The insulating material should have (a) low permittivity (b) high resistivity (c) high dielectric strength (d) all of the above
Last Answer : (d) all of the above
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 : In capacitance grading a homogeneous dielectric is used. (a) Yes (b) No
Last Answer : (b) No
Description : In capacitance grading of cables we use a ______ dielectric. (a) composite (b) porous (c) homogeneous (d) hygroscopic
Last Answer : (a) composite
Description : What are the disadvantages of paper insulation?
Last Answer : a. Absorbs moisture. b. Cable termination/sealing problems.
Description : Rubber is most commonly used insulation in cables. (a) Yes (b) No
Last Answer : (a) Yes
Description : The intersheaths 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
Last Answer : (c) provide proper stress distribution
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 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
Last Answer : (c) Voltage
Description : Which of the following insulation is used in cables? (a) Varnished cambric (b) Rubber (c) Paper (d) Any of the above
Last Answer : (d) Any of the above
Description : When measuring insulation resistance of cables using d.c. source, the galvanometer used should be initially short circuited because (A) Cables have a low value of capacitance which draws a high ... high value of charging current (D) Cables have a low value of capacitance and initial resistance
Last Answer : When measuring insulation resistance of cables using d.c. source, the galvanometer used should be initially short circuited because Cables have a high value of capacitance which draws a high value of charging current
Description : In a cable the voltage stress is maximum at (a) sheath (6) insulator (e) surface of the conductor (d) core of the conductor
Last Answer : (d) core of the conductor
Description : What is the type cable used in radiation areas?
Last Answer : Mineral insulated (MI) cables.
Description : What is the specified cable life?
Last Answer : 50 years.
Description : What are the purposes of cable trays?
Last Answer : a. Avoid sagging of cables b. Give mechanical support
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 : 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
Description : 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
Last Answer : (b) hysteresis and leakage losses only
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 : The surge resistance of cable is (a) 5 ohms (b) 20 ohms (c) 50 ohms (d) 100 ohms
Last Answer : (c) 50 ohms
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 : In case of three core flexible cable the colour of the neutral is (a) blue (b) black (c) brown (d) none of the above
Last Answer : (a) blue
Description : In a cable immediately above metallic sheath _____ is provided. (a) Earthing connection (b) Bedding (c) Armouring (d) None of the above
Last Answer : (b) Bedding
Description : The bedding on a cable consists of (a) Hessian cloth (b) Jute (c) Any of the above (d) None of the above
Last Answer : (c) Any of the above
Description : Which of the following protects a cable against mechanical injury? (a) Bedding (b) Sheath (c) Armouring (d) None of the above
Last Answer : (c) Armouring
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
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 : The velocity of travelling wave through a cable of relative permittivity 36 is
Last Answer : The velocity of travelling wave through a cable of relative permittivity 36 is 0.5 x 108 m/sec
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 : 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 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 : The metallic sheath may be made of lead or lead alloy or of aluminium. (a) Yes (b) No
Description : Polyethylene has very poor dielectric and ageing properties. (a) Yes (b) No
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