197. In a circuit breaker, arc is initiated by the process of
A. thermal emission
B. field emission
C. alternators
D. transmission lines

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198. Buchholz relay is used for the protection of
A. switch yard
B. transformers
C. alternators
D. transmission lines

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199. The basic problem in a circuit breaker is to
A. maintain the arc
B. extinguish the arc
C. emit ionization electrons
D. none of these

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200. In oil and air blast circuit breakers, the current zero interruption is attained by
A. lengthening of arc
B. cooling and blast effect
C. deionizing the oil with forced air
D. both A and B above

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201. Air blast circuit breaker is operated at a pressure of
A. 5 to 10 kg/cm2
B. 10 to 15 kg/cm2
C. 15 to 20 kg/cm2
D. 20 to 30 kg/cm2

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202. The voltage appearing across the contacts after the opening of the circuit breaker is called
A. surge voltage
B. recovery voltage
C. arc voltage
D. break open voltage

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203. Buchholz relays are used for transformers of ratings above
A. 100 kV
B. 200 kV
C. 500 kV
D. 1000 kV

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