For cost and safety, the outdoor substations are installed for voltages above

Magnetic circuit breaker has ______ trip action.

A. delayed

B. instantaneous

C. both of the above

D. none of the above

In a circuit breaker the basic problem is to

A. maintain the arc

B. extinguish the arc

C. transmit large power

D. emit the ionizing electrons

The arcing contacts in a circuit breaker are made of

A. copper tungsten alloy

B. porcelain

C. electrolytic copper

D. aluminium alloy

Air blast circuit breaker is used for

A. over currents

B. short duty

C. intermittant duty

D. repeated duty