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MCQ
61. Objectives of power system is/are-
Cost of electrical energy per kWh is to be minimum
Rated voltage and frequency has to be supplied to the consumers
both 1 and 2
nether 1 nor 2
62. Which of the following rotor is used in thermal power plants?
cylindrical rotor
salient pole rotor
squirrel cage rotor
either of these
ব্যাখ্যা: Cylindrical rotor is also called as round rotor or smooth rotor. This rotor is mechanically very strong It's used in thermal power plants.
63. Four identical alternators each are rated for 20 MVA, 11KV having a subtransient reactance of 16% are working in parallel. The short circuit level at the busbar is-
500 MVA
400 MVA
125 MVA
100 MVA
64. India's largest thermal power station is located at--
Madhya Pradesh
Neyveli
Kota
Chandrapur
65. Plog setting of a relay can be altered by varying-
air gap of magnetic path
adjustable back up stop
no. of ampere-turns
none of these
66. Interference between a power line and a communication line is due to-
electromagnetic induction
electrostatic induction
electromagnetic and electrostatic induction.
none of the above
ব্যাখ্যা: Interference is the process in which two or more light, sound or electromagnetic waves of the some frequency combine to reinforce or cancel each other. It is generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling or conduction
67. Suspension insulators are used when transmission voltage is-
high
low
fluctuating
steady
ব্যাখ্যা: When transmission voltage is greater than 33kV, thes suspension insulator is used. It is consist of a number of glass or porcelain dises connected in series by metal links in the form of a string.
68. Permissible variation in power frequency in Bangladesh is-
±0.1%
±1%
±5%
±10%
69. Routing means connecting-
Circuit or equipment to earth
Impent to earth
Circuit to earth
None of the above
ব্যাখ্যা: Routing is the process of selecting a path for traffic in network, circuits or different equipments.
70. Proximity effect is more in case of-
power cables
same in both cases
overhead lines
none of the above
ব‍্যাখ্যা: Proximity effect is more in case of power cables. because the distance between the conductor is small.
71. If the frequency is increased, then skin effect will—
increases
decreases
remains unaffected
any of the above
ব‍্যাখ্যা: The skin effect increases with the increase frequency
72. Length of the cable is doubled, its capacitance C will be-
one-fourth
doubled
one-half
unchanged
ব্যাখ্যা: The length of the cable and the capacitance of the cable are directly proportional to each other. If the length gets doubled, then the capacitance also can be doubled.
73. The skin effect shows that-
the distribution of AC current is uniform through the cross section of the conductor
current density is more at the centre of the condutor
current density is lower at the surface of the condutor
current density is more at the surface of the condutor
ব‍্যাখ্যা: The skin effect depends on the surface area of the conductor. The skin effect in the solid conductor is more than the stranded conductor because the solid conductor has more surface area.
74. Common declared distribution voltage in Bangladesh for low voltage circuit is-
230 Volts
250 Volts
440 Volts
380 Volts
75. When power is to be transmitted over a distance of 250km, the transmission voltage should be-
66kV
132kV
33kV
11kV
Transmission lines are three types-Short transmission line (A length less than 80 km (50 miles) and voltage level less than 69kV) Medium Transmission line (A length more than 80km (50 miles) but less than 250km (150 miles) and voltage level is from 69kV to 132kV) Long transmission line (A length more than 250 km (150 miles) and voltage level is above 132kV)
76. The volume of copper required for an ac transmission line is inversely proportional to-
current
voltage
power factor
both b & c
77. If the fault current is 2000A, the relay setting is 50% and CT ratio is 400: 5, then plug setting multiplier will be-
10
25
15
50
78. Which is used for power factor improvement?
Spring motor
Sychronous motor
Commutator motor
Squirrel case motor
ব্যাখ্যা: To improve power factor we ute- -Capacitor bank -Synchronous motor -Synchronous condenser -Phase advancer,
79. Find the number of strands of ACSR conductor for 4 layer transmission line.
1
67
37
2
80. Which distribution system is more reliable?
Ring main system
Tree system
Radial System
All are equally reliable
ব্যাখ্যা: The ring main distribution system is more reliable as each distribution transformer is fed with two feeders. That means in the event of a fault in any section of the feeder. the continuity of the supply is ensured from the alternative path.