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Consider the protection system shown in the figure below. The circuit breakers, numbered from 1 to 7 are of identical type. A single line to ground fault with zero fault impedance occurs at the midpoint of the line (at point F), but circuit breaker 4 fails to operate (“stuck br eaker”). I f the relays are coordinated correctly, a valid sequence of circuit breaker operations is
(a)
(b)
(c)
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- 1, 2, 6, 7, 3, 5
- 1, 2, 5, 6, 7, 3
- 5, 6, 7, 3, 1, 2
- 5, 1, 2, 3, 6, 7
Correct Option: C
If the relays are coordinated correctly, due to fault in a particular section, relay in that section must operate first, then relays in near by section if first relay fails. It is back up protection. Thus, the sequence is 5, 6, 7, 3, 1, 2.
