# Power Systems (Transmissions & Distribution) Expected MCQ PDF 4 For VIZAG MT Exam 2017

1)   The stay type of insulators is insulated at a height of not less than _________ m.
a. 5
b. 6
c. 3
d. 4

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

3)   Which type of insulators is used in guy wires?
a. Stay insulators
b. Shackle insulators
c. Pin type
d. Strain type

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
c. Cemented cap type
d. All of these

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

7)   Where is the suspension type of insulators mainly used?
a. RCC poles
b. Wooden poles
c. Steel poles
d. 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

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
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

11)   The string efficiency of a high voltage line is around ______.
a. 100 %
b. 80 %
c. 40 %
d. 10 %

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)
13)   Voltage across the string is ___________ times the line voltage.
a. √3
b. √2
c. 1 / √3
d. 1 / √2

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

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 %

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
19)   Which shielding is called the static shielding of the string?
a. Using the guard rings
c. Increasing the length of cross arms
d. None of these

20)   The insulators fail due to
a. Flash over
b. Short circuits
c. Deposition of dust
d. 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

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

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

25)   In case of dc voltage, which colour beads are formed near the negative conductor?
a. Reddish
b. Bluish
c. Greenish
d. Violet

26)   In case of dc voltage, smoother _____________ uniform glows near the positive conductor.
a. Yellow
b. Bluish white
c. Reddish white
d. Greenish yellow

27)   Which of the following statements are true related to corona?
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

28)   Which gas is formed near to the conductors by producing a hissing noise?
a. Oxygen
b. Ozone
c. Hydrogen
d. Nitrogen

29)   Corona is observed on
a. AC transmissions only
b. DC transmissions only
c. AC and DC transmissions
d. None of these

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)
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

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)
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

36)   By what factor does the critical disruptive voltage (Vd) get reduced?
a. 0.6
b. 0.7
c. 0.8
d. 0.9

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
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

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