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Faults in Power System - Multiple Choice Questions

Faults in Power System - Multiple Choice Questions Points : faults in power system, multiple choice questions and answers, electrical objective type question answers, mcqs 1. The ratings of circuit breakers are generally decided on the basis of
(i) unsymmetrical fault currents
(ii) symmetrical fault currents
(iii) normal circuit currents
(iv) none of above

2. The most common fault on an overhead transmission line is
(i) single line to ground fault
(ii) three phase short-circuited fault
(iii) double line to ground fault
(iv) line to line fault

3. Reactors are used at various locations in the power system to
(i) increase short-circuit current
(ii) avoid short-circuit current
(iii) limit short-circuit current
(iv) none of above

4. The most severe fault on the power system is
(i) three-phase short-circuit
(ii) line to line fault
(iii) double line to ground fault
(iv) single line to ground fault

5. In a balanced 3-phase system,
(i) only negative sequence current is zero
(ii) only zero sequence current is zero
(iii) both negative and zero sequence currents are zero
(iv) none of above

6. When all the three phases are short-circuited, the current thought the system is
(i) zero
(ii) low
(iii) very large
(iv) none of above

7. Reactors are connected with the system.
(i) in series
(ii) in parallel
(iii) in series-parallel
(iv) none of above

8. A 3-phase transmission line operating at 10 kV has a resistance of 1O. The percentage resistance of the line at 10,000 kVA base is
(i) 20%
(ii) 10%
(iii) 5%
(iv) 40%

9. The operator a rotates the vector in anticlockwise direction by
(i) 90°
(ii) 180°
(iii) 60°
(iv) 120°

10. The vector sum of positive sequence currents is
(i) zero
(ii) low
(iii) infinite
(iv) none of above

11. When a short circuit occurs in a power system
(i) the voltage at fault point is zero
(ii) a very large current flows in the system
(iii) it results in overheating of equipment
(iv) all of above

12. The zero sequence impedance of different elements of power system is generally
(i) zero
(ii) equal
(iii) different
(iv) none of above

13. The fault on a power system that gives symmetrical fault currents is
(i) line to tine fault
(ii) three-phase short circuit fault
(iii) single line to ground fault
(iv) none of above

14. -A 1000 kVA transformer has a reactance of 5%. Its reactance at2000 kVA base is
(i) 5%
(ii) 2.5%
(iii) 20%
(iv) 10%

15. The use of reactors permits the installation of circuit breakers of
(i) lower rating
(ii) same rating
(iii) higher rating
(iv) none of above

16. If the percentage reactance-of the system upto the fault point is 20% and base kVA is 10,000, then short-circuit kVA is
(i) 10.000 kVA
(ii) 50,000 kVA
(iii) 500 kVA
(iv) 30.000 kVA

17. Oil-immersed air-cored reactors are used as current-limiting reactors because
(i) they have higher safety against flash-over
(ii) they have higher thermal capacity
(iii) oil serves the purpose of cooling and insulation
(iv) all of above

18. The short-circuit kVA is maximum when fault occurs
(i) near the generator
(ii) at the end of transmission line
(iii) in the middle of transmission line
(iv) none of above

20. A short-circuit may lead to
(i) excessive current
(ii) fire or explosion
(iii) low voltage in the system
(iv) all of above

21. In short-circuit calculations, the selected base kVA is equal to
(i) that of the largest plant
(ii) the total plant capacity
(iii) any arbitrary value
(iv) all above

22. The positive and negative sequence impedance of a transmission line are
(i) equal
(ii) zero
(iii) different
(iv) infinite

23. The positive sequence impedance of a feeder is 3 ohm. Its negative sequence impedance will be
(i) 3 ohm
(ii) 1 ohm
(iii) 9 ohm
(iv) 6 ohm

24. On the occurrence of an unsymmetrical fault, the sequence component which is always greater than the negative sequence component is
(i) zero sequence component
(ii) positive sequence component
(iii) both (i) and (ii)
(iv) none of above

25. Cable and lines are mostly
(i) inductive
(ii) capacitive
(iii) resistive
(iv) none of above

26. The impedances of transformers and alternators are mostly
(i) resistive
(ii) inductive
(iii) capacitive
(iv) none of above

27. Unsymmetrical faults
(i) introduce unbalance in the system
(ii) indicate abnormal conditions in the System
(iii) are more frequent than symmetrical faults
(iv) all of above

28. Current-limiting reactors in power system have
(i) large resistance and low reactance
(ii) large reactance and low resistance
(iii) large reactance and resistance
(iv) none of above

29. The most severe unsymmetrical fault is
(i) single line-to-ground fault
(ii) line-to-line fault
(iii) double line-to-ground fault
(iv) none of above