274. Rate of rise of restriking voltage depends
A. type of circuit breaker.
B. inductance of the system only.
C. capacitance of the system only.
D. inductance and capacitance of the system.

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275. Breakdown strength of air at STP is 24 kV/cm. Its breakdown strength at 30?C and 72 cm of Hg wil be
A. 24.25 kV/cm.
B. 20.2 kV/cm.
C. 23 kV.
D. 49.5 kV/cm.

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276. Capacitor switching is easily done with
A. air blast circuit breaker.
B. oil C.B.
C. vacuum C.B.
D. any one of the above.

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277. The normal practice to specify the making current of a circuit breaker is in terms of
A. r.m.s. value
B. peak value
C. average value
D. both r.m.s. and peak value.

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278. Chances of arc interruption in subsequent current zero
A. increases in case of OCB.
B. decreases in case of OCB
C. interruption is always at first current zero (in OCB)
D. none of these

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279. If the inductance and capacitance of a system are 4 H and 0.04 tif respectively and the instantaneous value of current interrupted is 40 amps, the value of shunt resistance across the breaker for critical damping is
A. 400 k12
B. 40 kf2
C. 5k
D. 4 kf2

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280. For effective use of a counterpoise wire
A. its leakage resistance should be greater than the surge impedance.
B. three-phase and two-earth fault relays are required.
C. tow-phase and two-earth fault relays are required.
D. two-phase and one-earth fault relays are required.

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