Power System Multiple Choice Questions

1. For an overhead line, the surge impedance is taken as

(a) 20 – 40 ohm.
(b) 70 – 80 ohms
(c) 100 – 200 ohms
(d) 500 -1000 ohms


Answer: (c) 100 – 200 ohms
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2. The presence of ozone due to corona is harmful because it

(a) reduces power factor
(b) corrodes the material
(c) transfer energy to the ground
(d) none of the above.


Answer: (b) corrodes the material
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3. A feeder, in a transmission system, feeds power to

(a) distributors
(b) generating stations
(c) service mains
(d) all of the above.


Answer: (a) distributors
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4. The power transmitted will be maximum when

(a) corona losses are minimum
(b) reactance is high
(c) sending end voltage is more
(d) receiving end voltage is more.


Answer: (c) sending end voltage is more
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5. A 3-phase 4 wire system is commonly used on

(a) primary transmission
(b) secondary transmission
(c) primary distribution
(d) secondary distribution.


Answer: (d) secondary distribution.
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6. Which of the following is not a constituent for making porcelain insulators?

(a) Quartz
(b) Kaolin
(c) Felspar
(d) Silica


Answer: (d) Silica
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7. There is a great possibility of occurrence of corona during

(a) dry weather
(b) winter
(c) summer heat
(d) humid weather.


Answer: (d) humid weather.
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8. Which of the following relays is used on long transmission lines? Impedance relay

(a) Mho’s relay
(b) Reactance relay
(c) None of the above.


Answer: (a) Mho’s relay
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9. The steel used in steel cored conductors is usually

(a) alloy steel
(b) stainless steel
(c) mild steel
(d) high speed steel


Answer: (c) mild steel
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10. Which of the following distribution system is more reliable ?

(a) Radial system
(b) Tree system
(c) Ring main system
(d) All are equally reliable


Answer: (c) Ring main system
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11. Transmission voltage of 11 kV is normally used for distances up to

(a) 20 – 25 km
(b) 40 -50 km
(c) 60 -70 km
(d) 80 – 400 km


Answer: (a) 20 – 25 km
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12. Which of the following regulations is considered best?

(a) 50%
(b) 20%
(c) 10%
(d) 2%


Answer: (d) 2%
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13. Skin effect is proportional to

(a) (conductor diameter)4
(b) (conductor diameter)3
(c) (conductor diameter)2
(d) (conductor diameter)1/2
(e) none of the above.


Answer: (c) (conductor diameter)2
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14. In A.C.S.R conductors, the insulation between aluminum and steel conductors is

(a) insulin
(b) bitumen
(c) varnish
(d) no insulation is required


Answer: (d) no insulation is required
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15. Which of the following bus-bar schemes has the lowest cost?

(a) Ring bus-bar scheme
(b) Single bus-bar scheme
(c) Breaker and a half scheme
(d) Main and transfer scheme


Answer: (b) Single bus-bar scheme
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16. Owing to skin effect

(a) current flows through the half cross-section of the conductor
(b) portion of the conductor near the surface carries more current and core of the conductor carries less current
(c) portion of the conductor near the surface carries less current and core of the conductor carries more current
(d) any of the above


Answer: (b) portion of the conductor near the surface carries more current and core of the conductor carries less current
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17. By which of the following methods string efficiency can be improved ?

(a) Using a guard ring
(b) Grading the insulator
(c) Using long cross arm
(d) Any of the above


Answer: (d) Any of the above
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18. In aluminum conductors, steel core is provided to

(a) compensate for skin effect
(b) neutralize proximity effect
(c) reduce line inductance
(d) increase the tensile strength


Answer: (d) increase the tensile strength
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19. By which of the following a bus-bar is rated ?

(a) Current only
(b) Current and voltage
(c) Current, voltage and frequency
(d) Current, voltage, frequency and short time current


Answer: (d) Current, voltage, frequency and short time current
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20. A circuit is disconnected by isolators when

(a) line is energized
(b) there is no current in the line
(c) line is on full load
(d) circuit breaker is not open


Answer: (b) there is no current in the line
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21. For which of the following equipment current rating is not necessary ?

(a) Circuit breakers
(b) Isolators
(c) Load break switch
(d) Circuit breakers and load break switches


Answer: (b) Isolators
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22. In a substation the following equipment is not installed

(a) exciters
(b) series capacitors
(c) shunt reactors.


Answer: (a) exciters
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23. Overhead lines generally use

(a) copper conductor
(b) all aluminium conductors
(c) A.C.S.R. conductors
(d) none of these.


Answer: (c) A.C.S.R. conductors
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24. The minimum clearance between the ground and a 220 kV line is about

(a) 4.3 m
(b) 5.5 m
(c) 7.0 m
(d) 10.5 m


Answer: (c) 7.0 m
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25. Corona usually occurs when the electrostatic stress in air around the conductor exceeds

(a) 6.6 kV (RMS value)/cm
(b) 11 kV (RMS value)/cm
(c) 22 kV (maximum value)/cm
(d) 30 kV (maximum value)/cm


Answer: (d) 30 kV (maximum value)/cm
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26. The use of strain type insulators is made where the conductors are

dead ended

(a) at Intermediate anchor towers
(b) any of the above
(c) none of the above.


Answer: (b) any of the above
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27. The current drawn by the line due to corona losses is

(a) non-sinusoidal
(b) sinusoidal
(c) triangular
(d) square


Answer: (a) non-sinusoidal
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28. Pin type insulators are generally not used for voltages beyond

(a) I kV
(b) I I kV
(c) 22 kV
(d) 33 kV


Answer: (d) 33 kV
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29. Aluminum has a specific gravity of

(a) 1.5
(b) 2.7
(c) 4.2
(d) 7.8


Answer: (b) 2.7
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30. For transmission of power over a distance of 200 km, the transmission voltage should be

(a) 132 kV
(b) 68 kV
(c) 33 kV
(d) II kV


Answer: (a) 132 kV
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Power System Multiple Choice Questions

 

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