400 Important Transmission and Distribution MCQ Question and Answer | PDF Free Download
1.The purpose of guard ring in transmission lines is to
- AReduce the earth capacitance of the lowest unit
- BIncrease the earth capacitance of the lowest unit
- CReduce the transmission line losses
- DNone of the above
2.Which of the following statements is true regarding corona ?
- ACorona takes place at a voltage lower than breakdown voltage.
- BCorona takes place at a voltage higher than breakdown voltage.
- CCorona is a current phenomenon.
- DCorona increases the transmission line efficiency.
3.The effect of corona can be detected by
- APresence of ozone detected by odour
- BHissing sound
- CFaint luminous glow of bluish colour
- DAll of the above
4.Corona loss in a transmission line increases with
- ADecrease in conductor size and increase in supply frequency.
- BIncrease in both conductor size and supply frequency.
- CDecrease in both conductor size and supply frequency.
- DIncrease in conductor size and decrease in supply frequency.
5.The good effect of corona on overhead lines is to
- AIncrease the line carrying capacity due to conducting ionised air envelope around the conductor.
- BIncrease the power factor due to corona loss.
- CReduce the radio interference from the conductor.
- DReduce the steepness of surge fronts.
6.Compared with a solid conductor of the same radius, corona appears on a stranded conductor at a lower voltage, because stranding
- AAssists ionisation
- BMakes the current flow spirally about the axis of the conductor
- CProduces oblique sections to a plane perpendicular to a axis of the conductor
- DProduces surfaces of smaller radius
7.Corona loss can be reduced by the use of hollow conductors because
- AThe current density is reduced
- BThe eddy current in the conductor is eliminated
- CFor a given cross section, the radius of the conductor is increased.
- DOf better ventilation in the conductor
8.Corona occurs between two transmission conductors when they
- AHave high potential difference
- BAre closely spaced
- CCarry dc power
- DBoth (a) and (b)
9.The corona occurs in humid weather at a voltage
- AMuch less than that needed in fair weather
- BMuch higher than that needed in fair weather
- CEqual to that needed in fair weather
- DNone of the above
10.The effect of corona in a transmission line is
- AIncreased energy loss
- BIncreased reactance
- CIncreased inductance
- DAll of the above
11.The charging current in a transmission line increases due to corona effect because corona increases
- ALine current
- BEffective line voltage
- CPower loss in lines
- DThe effective conductor diameter
12.The chances of occurrence of corona are maximum during
- AHumid weather
- BDry weather
- CWinter
- DHot summer
13.Corona is likely to occur maximum in case of
- ADistribution lines
- BTransmission lines
- CDomestic wiring
- DService mains
14.The only advantage of corona is that it
- AProduces a pleasing luminous glow
- BMakes line current sinusoidal
- CWorks as a safety valve for surges
- DOzone gas is produced
15.Presence of ozone owing to corona
- AImproves the pf
- BReduces the pf
- CCorrodes the material
- DImproves regulation
16.The approximate breakdown strength of atmospheric air at N.T.P. is
- A0.3 kV/cm
- B1.0 kV/cm
- C3 kV/cm
- D30 kV/cm
17.Disruptive corona begins in smooth cylindrical conductors in air at NTP if the electric field intensity at the conductor surface goes up to
- A21.1 kV(rms)/cm
- B21.1 kV(peak)/cm
- C21.1 kV(average)/cm
- D21.1 kV(rms)/m
18.The dielectric strength of air is
- AProportional to barometric pressure
- BProportional to absolute temperature
- CInversely Proportional to barometric pressure
- DNone of the above
19.Visual critical voltage is
- ALower than disruptive critical voltage
- BHigher than disruptive critical voltage
- CEqual to critical voltage
- DNone of the above
20.Critical voltage limit of a transmission line is increased by
- AIncreasing the radius of the conductors
- BIncreasing the spacing between conductors
- CReducing the spacing between conductors
- DReducing the radius of the conductors