# Power System Protection MCQs Part 3

a. The rate of rise of restriking voltage is usually expressed in terms of:

1. V / s
2. kV / ms
3. kV / µs
4. MV/ns

Correct answer: 3. kV / µs

b. It is desired to chop 20 A current in a circuit having L = 4 mH, C = 0.2 µC. Find the induced voltage.

1. 10 kV
2. 3.72 kV
3. 2.8 kV
4. 1.7 kV

Solution = i √(L/C) = 20 A * √(4 mH/0.2 uC) = 2.8 kV

c. Fault diverter is actually a:

1. Fuse
2. Circuit breaker
3. Relay
4. Switch

3. The fault diverter is actually a fast switch.

d. The major advantage associated with the static digital relay is:

1. Less sensitive
2. Performance speed is slow
3. It is expensive
4. It is not accurate

Correct answer: 3. It is expensive

e. Fusing factor of a fuse is mathematically defined by the equation:

1. Current rating of fuse * 4.44
2. 1/Current rating of the fuse
3. Min fusing current / Current rating of the fuse
4. Min fusing current * Current rating of the fuse

Correct answer: 3. Min fusing current / Current rating of the fuse

f. The correct statement about Sulphur Hexaflouride gas:

1. It provides free electrons to the breaker
2. It absorbs free electrons
3. It increases current flow the through the arc
4. None of these

Correct answer: 2. It absorbs free electrons

g. The correct equation which explains the breaking capacity of single phase circuit breaker:

1. V × I × 10−1 MVA
2. V × I × 10−3 MVA
3. V × I × 10−6 MVA
4. V × I × 10−9 MVA

Correct answer: 3. V × I × 10−6 MVA

h. The __________ the current, the ___________ is the time required by fuse to blow up:

1. Greater, smaller
2. Greater, Greater
3. Smaller, Smaller
4. All of these are possible

i. Usually the earth relays have ___________ current settings:

1. Lower
2. Higher
3. Both
4. None