Power System Protection MCQs Part 8

a. A power system contains two relays of 5 VA and 10 VA. The correct statement about the sensitivity of relays:

1. 5 VA relay is more sensitive than 10 VA
2. 10 VA relay is more sensitive than 5 VA
3. Both are equally sensitive
4. One can’t determine sensitivity from VA

Correct answer: 1. 5 VA relay is more sensitive than 10 VA

b. An overcurrent relay has setting of 200% and is connected to a transformer of 200/5. Find the pickup value.

1. 2.5 A
2. 5 A
3. 10 A
4. 20 A

Correct answer: 3. 10 A

c. The isolator is installed in power system to:

1. Protect against high current faults
2. Isolate a part of the system
3. Protect the buses
4. Separate a CT from PT

Correct answer: 2. Isolate a part of the system

d. The term inverted running represents an alternator:

1. Which is protected via inversion circuit
2. Which runs at a very high speed
3. A turboalternator which uses inverter circuits
4. Which behaves as a motor

Correct answer: 3. Which behaves as a motor

e. The making capacity of the circuit breaker is measured in terms of ______:

1. R.M.S
2. Peak
3. Both
4. None

Correct answer: 2. Peak

f. Mathematically the making capacity is defined by the equation:

1. 1.88 × Symmetrical breaking capacity
2. 2.55 × Symmetrical breaking capacity
3. 3.87 × Symmetrical breaking capacity
4. 4.99 × Symmetrical breaking capacity

Correct answer: 2. 2·55 × Symmetrical breaking capacity

g. The desired quantity in a fuse is:

1. High conductivity
2. Low conductivity
3. High melting point
4. High deterioration rate

Correct answer: 1. High conductivity

h. The correct relationship between the fusing current and diameter of the wire is:

1. I = k d
2. I = k d^1.5
3. I = k d²
4. I = k d³

Correct answer: 2. I = k d^1.5

i. The basic function of a relay is to:

1. Detect the fault
2. Interrupt the circuit
3. Both of these
4. None of these

Correct answer: 1. Detect the fault

j. A three phase 1000 MVA circuit breaker, 11 kVA has symmetrical breaking current:

1. 90909 A
2. 11000 A
3. 52486 A
4. 44088 A

Correct answer: 3. 52486 A

Solution: I = 1000 MVA / (11 kVA * √3) = 52486 A

Continue reading:

• Power System Protection MCQs Part 1
• Power System Protection MCQs Part 2
• Power System Protection MCQs Part 3
• Power System Protection MCQs Part 4
• Power System Protection MCQs Part 5
• Power System Protection MCQs Part 6
• Power System Protection MCQs Part 7
• Power System Protection MCQs Part 8
• Power System Protection MCQs Part 9
• Power System Protection MCQs Part 10