[ENG] What is the meaning of Circuit Breaker (CB) operating sequence of “O – t – CO – t’ – CO” ?

As per IEC 62271-100,
The rated characteristics of the circuit-breaker are referred to the rated operating sequence. There are two alternative rated operating sequences as follows:

a. O – t – CO – t’ – CO

Unless otherwise specified:
t  = 3 min for circuit-breakers not intended for rapid auto-reclosing;
t  = 0,3 s for circuit-breakers intended for rapid auto-reclosing (dead time);
t’ = 3 min.
NOTE:
Instead of t’ = 3 min, other values: t’ = 15 s and t’ = 1 min are also used for circuit-breakers intended for rapid auto-reclosing.

b. CO – t” – CO

with:
t” = 15 s for circuit-breakers not intended for rapid auto-reclosing
where
O represents an opening operation;
CO represents a closing operation followed immediately (that is, without any intentional delay) by an opening operation;
t, t’ and t” are time intervals between successive operations;
t and t’ should always be expressed in minutes or in seconds and
t” should always be expressed in seconds.
If the dead time is adjustable, the limits of adjustment shall be specified.
Example:
O – 0.3s – CO – 3m – CO
“O – 0.3s – C” means the operation time needed for the circuit breaker (CB) from OPEN position into CLOSE position within initial condition (no operation happened before, means the closing spring was already charged before). In this case, it is 0.3 seconds, which means the circuit breaker (CB) is intended for rapid auto-reclosing.
“CO” actually means “C – 0.03s – O”, since the period between CLOSE and OPEN is very short (0.03s), it is just written as “CO”. Operation time between CLOSE to OPEN shall be as short as possible, just in case a fault happened right after closing the circuit breaker (CB), then the circuit breaker (CB) shall be capable to OPEN immediately.
“O – 3m – C” means the operation time needed for the circuit breaker (CB) from OPEN position into CLOSE position at the second consecutive CLOSE after the first CLOSE. It requires for charging the closing spring. Short time in charging the closing spring can also be used for the circuit breaker (CB) intended for rapid auto-reclosing.



(Gathered from many sources)

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