Power Systems Transmissions Part 3
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Attempt Free Power Systems Transmissions Part 3 Here. Read The Important Electrical MCQ From Below.
1) The stay type of insulators is insulated at a height of not less than _________ m.
a. 5
b. 6
c. 3
d. 4
ANSWER: 3
2) Post type insulators are generally used in lines operating
a. Above 100 kV
b. Below 33 kV
c. At any voltage level
d. None of these
ANSWER: At any voltage level
Power Systems Transmissions Part 3
3) Which type of insulators is used in guy wires?
a. Stay insulators
b. Shackle insulators
c. Pin type
d. Strain type
ANSWER: Stay insulators
4) Assertion (A): Glazing on ceramic insulators is done to make it smooth and non – absorbent.
Reason (R): Moisture from atmosphere collects on the surface causing electrical breakdown.
a. Both A and R are true and R is the correct explanation of A
b. Both A and R are true and R is not the explanation of A
c. A is true but R is false
d. A is false but R is true
ANSWER: Both A and R are true and R is the correct explanation of A
5) The types of suspension insulators are
a. Hewlett type
b. Inter linking type
c. Cemented cap type
d. All of these
ANSWER: All of these
Power Systems Transmissions Part 3
6) Each disc in a suspension type of insulators is designed for what voltage?
a. 33 kV
b. 22 kV
c. 11 kV
d. 66 kV
ANSWER: 11 kV
7) Where is the suspension type of insulators mainly used?
a. RCC poles
b. Wooden poles
c. Steel poles
d. Steel towers
ANSWER: Steel towers
8) The voltage across the various discs of a string of suspension insulators having identical discs is different due to
a. Surface leakage currents
b. Series capacitance
c. Shunt capacitance to ground
d. Series and shunt capacitance
ANSWER: Shunt capacitance to ground
9) On what factor does the string efficiency of a string of suspension insulators is dependent?
a. Size of the insulator
b. Number of discs in the string
c. Size of tower
d. None of these
ANSWER: Number of discs in the string
Power Systems Transmissions Part 3
10) The maximum voltage of the disc type insulators is at
a. Same at all points
b. Near the tower or starting of the insulator
c. Near to the conductors
d. None of these
ANSWER: Near to the conductors
11) The string efficiency of a high voltage line is around ______.
a. 100 %
b. 80 %
c. 40 %
d. 10 %
ANSWER: 100 %
12) What is the voltage across the second unit from the top in case of a suspension type insulator?
a. V2 = V1 (3 + 4K)
b. V2 = V1 (1 + K)
c. V2 = V1 (1 + K2)
d. None of these
ANSWER: V2 = V1 (1 + K)
Power Systems Transmissions Part 3
13) Voltage across the string is ___________ times the line voltage.
a. √3
b. √2
c. 1 / √3
d. 1 / √2
ANSWER: √3
14) In a test by Murray loop for ground fault on 500 m of cable having a resistance of 1.6 Ω / km, the faulty cable is looped with the sound cable of some length and area of cross section. If the ratio of the other two arms of the testing network at balance is 3:1, what is the distance of fault from the testing end of cables?
a. 100 m
b. 200 m
c. 250 m
d. 300 m
ANSWER: 250 m
15) A 3 phase over head transmission line is supported by three discs of suspension insulators. The potentials across the first and second insulator are 8 and 11 kV respectively. What is the line voltage and string efficiency?
a. 0.654 and 63.5%
b. 0.375 and 68.3 %
c. 0.527 and 56.34 %
d. 0.287 and 65.258 %
ANSWER: 0.375 and 68.3 %
Power Systems Transmissions Part 3
16) What is the purpose of guard ring?
a. Reduce the earth capacitance of the lowest unit.
b. Increase the earth capacitance of the lowest unit.
c. Reduce the transmission line losses.
d. None of these.
ANSWER: Reduce the earth capacitance of the lowest unit.
17) Assertion (A): The string efficiency can be improved by using long cross arms.
Reason (R): Use of long cross arms reduces the ratio of capacity to earth to capacity per insulator thereby increasing the string efficiency.
a. Both A and R are true and R is the correct explanation of A
b. Both A and R are true and R is not the explanation of A
c. A is true but R is false
d. A is false but R is true
ANSWER: Both A and R are true and R is the correct explanation of A
18) Assertion (A): Capacitance grading improves the string efficiency not more than 220 kV.
Reason (R): In capacitance grading the units used are of different capacitance and so are not interchangeable.
a. Both A and R are true and R is the correct explanation of A
b. Both A and R are true and R is not the explanation of A
c. A is true but R is false
d. A is false but R is true
ANSWER: A is false but R is true
Power Systems Transmissions Part 3
19) Which shielding is called the static shielding of the string?
a. Using the guard rings
b. Grading the insulators
c. Increasing the length of cross arms
d. None of these
ANSWER: Using the guard rings
20) The insulators fail due to
a. Flash over
b. Short circuits
c. Deposition of dust
d. All of these
ANSWER: All of these
21) The number of discs required for 220 kV ac over head transmission line in clear atmosphere is
a. 10 – 12
b. 21 – 22
c. 12 – 14
d. 5 – 6
ANSWER: 12 – 14
22) At what angle is the water sprayed on the insulator in 50 cycle wet test?
a. 35 °C
b. 40 °C
c. 45 °C
d. 50 °C
ANSWER: 45 °C
Power Systems Transmissions Part 3
23) What is the value of the wave front and the wave tail of the standard lightning impulse wave used in the impulse voltage withstand test?
a. 50 μ sec and 1.2 μ sec
b. 1.2 μ sec and 50 μ sec
c. 50 μ sec and 2.1 μ sec
d. 2.1 μ sec and 50 μ sec
ANSWER: 1.2 μ sec and 50 μ sec
24) What is corona?
a. Partial breakdown of air
b. Complete breakdown of air
c. Sparking between the lines
d. None of these
ANSWER: Complete breakdown of air
25) In case of dc voltage, which colour beads are formed near the negative conductor?
a. Reddish
b. Bluish
c. Greenish
d. Violet
ANSWER: Reddish
Power Systems Transmissions Part 3
26) In case of dc voltage, smoother _____________ uniform glows near the positive conductor.
a. Yellow
b. Bluish white
c. Reddish white
d. Greenish yellow
ANSWER: Bluish white
27) Which of the following statements are true related to corona?
1. It causes radio interference.
2. It attenuates lightning surges.
3. It causes power loss.
4. It amplifies switching surges.
The codes are:
a. 1,2,4
b. 1,4
c. 1,2,3
d. 2,3
ANSWER: 1,2,3
Power Systems Transmissions Part 3
28) Which gas is formed near to the conductors by producing a hissing noise?
a. Oxygen
b. Ozone
c. Hydrogen
d. Nitrogen
ANSWER: Ozone
29) Corona is observed on
a. AC transmissions only
b. DC transmissions only
c. AC and DC transmissions
d. None of these
ANSWER: AC and DC transmissions
30) Air density factor which depends on the pressure and temperature is given by which of these formulas?
a. δ = (5.92 * b) / (273 + t)
b. δ = (7.92 * b) / (273 + t)
c. δ = (3.92 * b) / (273 + t)
d. δ = (4.92 * b) / (273 + t)
ANSWER: δ = (3.92 * b) / (273 + t)
Power Systems Transmissions Part 3
31) What happens if the voltage applied is equal to the critical disruptive voltage?
a. Corona does not start
b. Corona starts but is not visible
c. Corona starts and is visible
d. Only ionization starts
ANSWER: Corona starts but is not visible
32) What is the value of energy distance in case of two parallel conductors?
a. (r + 0.301 * √ r)
b. (r + 0.308 * √ r)
c. (r + 0.501 * √ r)
d. (r + 0.508 * √ r)
ANSWER: (r + 0.301 * √ r)
33) As the moisture content in the air increases, what is the effect of this on the disruptive critical voltage?
a. Increases
b. Decreases
c. Remains constant
d. May increases or decrease
ANSWER: Decreases
34) What is the value of energy distance in case of co-axial conductors?
a. (r + 0.301 * √ r)
b. (r + 0.308 * √ r)
c. (r + 0.501 * √ r)
d. (r + 0.508 * √ r)
ANSWER: (r + 0.308 * √ r)
Power Systems Transmissions Part 3
35) What is the critical disruptive voltage of a three phase line which has a conductor of 2 cm in diameter which are spaced equilaterally 1m apart, if the dielectric strength of air is about 30 kV/cm, and air density about 0.952 and irregularity factor 0.9?
a. 152.36 kV
b. 146.235 kV
c. 144.95 kV
d. 111.235 kV
ANSWER: 144.95 kV
36) By what factor does the critical disruptive voltage (Vd) get reduced?
a. 0.6
b. 0.7
c. 0.8
d. 0.9
ANSWER: 0.8
37) Higher the frequency, _____________.
a. Lower the corona loss
b. Higher is the corona loss
c. Does not effect
d. Depends on the physical conditions
ANSWER: Higher is the corona loss
Power Systems Transmissions Part 3
38) Which harmonics are generated during the corona, which leads to the increase in corona losses?
a. Third harmonics
b. Fifth harmonics
c. Seventh harmonics
d. None of these
ANSWER: Third harmonics
39) What is the use of bundled conductors?
a. Reduces surface electric stress of conductor
b. Increases the line reactance
c. Decreases the line capacitance
d. None of these
ANSWER: Reduces surface electric stress of conductor
40) On which factor is the corona loss dependent?
a. Material of the conductor
b. Diameter of the conductor
c. Height of the conductor
d. None of these
ANSWER: Diameter of the conductor
Power Systems Transmissions Part 3
