Q.1 Which of the following information is necessary to obtain for design of substation earthing grid for substation?
A. maximum earth fault current, fault clearing time
B. Area covered by the substation
C. Resistivity of the soil at the sub-station site
D. All of the above
Ans.: D
Q.2 The degree of protection provided by a grounding system under lightning discharge conditions depends upon its _____ rather than on power frequency impedance.
A. Resistance
B. impulse impedance
C. reactance
D. all of the above
Ans.: B
Q.3 What is impulse impedance?
A. The impedance under normal conditions
B. The impedance under impulse conditions
C. The impulse under transient conditions
D. All of the above
Ans.: B
Q.4 The impulse impedance is always ____ than its power frequency impedance.
A. lower
B. higher
C. equal
D. any of the above
Ans.: B
Q.5 Resistivity of water depends on the ___ and ____ of salt dissolved in it.
A. amount, nature
B. temperature, nature
C. purity, nature
D. none of the above
Ans.: A
Q.6 Pure water is poor conductor of_____.
A. temperature
B. sound
C. electricity
D. all of the above
Ans.: C
Q.7 Which of the following is/are correct for effect of current flowing through human body?
A. Below 1 mA = nothing
B. 11 to 25 mA = painful shock with muscle contraction after medical treatment they can restoed
C. Above 150 mA = cardiac arrest, body starts burning resulting into death
D. All of the above
Ans.: D
Q.8 Current flows from earthing grid during ____ creating potential difference.
A. operation and working
B. faults
C. lighting
D. all of the above
Ans.: D
Q. 9 Impulse performance of earthing system depends on which of the following factors?
A. Electrical soil properties
B. ground electrode geometry
C. current waveform properties
D. all of the above
Ans.: D
Q.10 Tower footing resistance should be below ___.
A. 10 Ω
B. 50 Ω
C. 40 Ω
D. 20 Ω
Ans.: A
Q.11 Material used for tower footing can be____.
A. iron clad
B. copper plates
C. Both A and B
D. tungsten
Ans.: C
Q.12 ____ is very good in improving or increasing the conductivity of soil as compared to others.
A. Sea water
B. pure water
C. Common salt
D. Drinking water
Ans.: C
Q.13 A human body can tolerate a current slightly higher than ___.
A. 10 Hz
B. 5 Hz
C. 15 Hz
D. 25 Hz
Ans.: D
Q.14 If the depth of earth electrode is increases, the value of ground resistance can be____.
A. increases
B. minimized
C. does not depend on the depth of electrode
D. none of the above
Ans.: B
Q.15 Which of the following common paths for current to flow through the body?
A. Hand to foot
B. Hand to hand through the chest
C. Foot to foot
D. all of the above
Ans.: D