Switchgear and protection. Part – 3

21. An isolator is designed to open a circuit under

A. Full-load

B. Normal condition

C. No-load

D. None of the above

22. The operating time of a fuse is about

A. 0.002 sec

B. 1 sec

C. 0.8 sec

D. 1.5 sec

23. The transient stability limit of a power system can be appreciably increased by introducing

A. Series inductance

B. Shunt inductance

C. Series capacitance

D. Shunt capacitance

24. In a bulk oil circuit breaker, the oil actually used for arc extinction is about

A. 60% of total

B. 40% of total

C. 90% of total

D. 10% of total

25. When a line-to-ground fault occurs, the current in the faulted phase is 100A. The zero sequence current in this case is

A. 33.3 A

B. Zero

C. 66.6 A

D. 100 A

26. Under dry conditions, the resistance offered by the human body may be as high as

A. 200 Ω

B. 100 Ω

C. 100000 Ω

D. 250 Ω

27. An over current relay having current setting of 125% is connected to a supply circuit through a current transformer of 400/5A. The pick-up current is

A. 6.25A

B. 12.55A

C. 3.125A

D. 25A

28. The arc voltage in a circuit breaker

A. Is in phase with arc current

B. Lags arc current by 90⁰

C. Leads arc current by 90⁰

D. Lags arc current by 180⁰

29. A circuit breaker is a

A. Current controlling device

B. Circuit interrupting device

C. Current limiting device

D. None of the above

30. The following contact is largely used for low-voltage oil circuit breaker

A. Tulip type contacts

B. Finger and wedge contacts

C. Butt contact

D. None of the above