Description : The armature of a dc machine is laminated to reduce: (A) Eddy current loss (B) Hysteresis loss (C) copper losses (D) friction and windage losses
Last Answer : Ans: A Thinner the laminations, greater is the resistance offered to the induced e.m.f., smaller the current and hence lesser the I2R loss in the core.
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 : 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 : 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
Last Answer : (a) avoid excessive sheath losses
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
Last Answer : (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 : 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 : 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 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 : 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 : 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 : 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 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 : 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 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 : Why bimetallic washers provided in aluminium copper transition joints?
Last Answer : To avoid galvanic corrosion failure.
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 : Which of the following losses is/are present in every direct current generator armature? A. Winding copper loss B. Core eddy current loss C. Magnetic hysteresis loss D. All of the above.
Last Answer : Answer: D
Description : 70] Silicon steel used in laminations mainly reduces A. Hysteresis loss B. Eddy current losses C. Copper loss D. All of the above
Last Answer : A. Hysteresis loss
Description : 42 The efficiency of a transformer will be maximum when A. copper losses = hysteresis losses B. Hysteresis losses = eddy current losses C. Eddy current losses = copper losses D. Copper losses = iron losses
Last Answer : D. Copper losses = iron losses
Description : As an armature revolves within a magnetic field, friction is developed between the rotated magnetized particles as they pass through each magnetization cycle. This results in ____________. A. copper loss B. eddy-current loss C. hysteresis loss D. armature reaction
Last Answer : Answer: C
Description : 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°
Last Answer : (b) leads the voltage by 90°
Description : 7 The main advantage of auto transformer over a two winding transformer is A. Hysteresis losses are reduced B. Saving in winding material C. Copper losses are negligible D. Eddy losses are totally eliminated
Last Answer : A) hysteresis losses is reduced
Description : The upper pulse rate and information carrying capacity of a cable is limited by a. Pulse shortening b. Attenuation c. Light leakage d. Modal dispersion
Last Answer : d. Modal dispersion
Description : The upper pulse rate and information-carrying capacity of a cable is limited by ∙ A. pulse shortening ∙ B. attenuation ∙ C. light leakage ∙ D. modal dispersion
Last Answer : D. modal dispersion
Description : The upper pulse rate and information carrying capacity of a cable is limited by ∙ a. Pulse shortening ∙ b. Attenuation ∙ c. Light leakage ∙ d. Modal dispersion
Last Answer : ∙ d. Modal dispersion
Description : The use of four diodes, in a full-wave bridge rectifier circuit, will __________. A. provide unidirectional current to the load B. allow a very high leakage current from the load C. convert direct current to alternating current D. offer high opposition to current in two directions
Last Answer : Answer: A
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 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 : The metallic sheath may be made of lead or lead alloy or of aluminium. (a) Yes (b) No
Last Answer : (b) No
Description : Polyethylene has very poor dielectric and ageing properties. (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