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1.0.0
MCQ
61. ACSR means-
Aluminium core steel reinforced
Aluminium conductor steel reinforced
Aluminium copper steel reinforced
reinforced all conductor steel
ব‍্যাখ্যা: ACSR = Aluminium conductor steel reinforced.
62. 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
63. 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
64. Common declared distribution voltage in Bangladesh for low voltage circuit is-
230 Volts
250 Volts
440 Volts
380 Volts
65. 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
66. The volume of copper required for an ac transmission line is inversely proportional to-
current
voltage
power factor
both b & c
67. 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)
68. 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.
69. 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.
70. 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
71. 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.
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. 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
74. India's largest thermal power station is located at--
Madhya Pradesh
Neyveli
Kota
Chandrapur
75. The skin effect of conductor will increase when-
diameter decrease
resistivity decrease
frequency decrease
all of the above
76. 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,
77. Find the number of strands of ACSR conductor for 4 layer transmission line.
1
67
37
2
78. The presence of earth in case of overhead lines-
increase inductance
increase capacitance
decrease inducatance
decrease capacitance
ব‍্যাখ্যা: As the earth is considered to be an infinite source of electrons, the presence of overhead lines causes charge currier to be separated by a dielectric (air), causing an increase in capacitance.
79. 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
80. 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.