The operating sequences are given by IEC 62271-100.
The circuit breakers can operate with the 3 operating sequences mentioned in the respective catalogues.

The short circuit breaking and making tests and the mechanical tests have been performed with the operating sequence “O-0.3s-CO-15s-CO”
It is the “fast” operating sequence, the most severe from IEC standard.

So, the circuit breaker can also performed the two other operating sequences (see below)
O - 3 min - CO-3 min - CO
O - 0.3 s - CO-3 min - CO
O - 0.3 s - CO-15 s - CO

The different operating squences indicate the different protection functionality. Such as CBs with rapid-recloser squences with t=0.3s, they can switch off the short-circuit current for 2 times in a very short time.

Following is the definition from IEC standard:
The rated operating sequence is O – t – CO – t' – CO, where
O represents an opening operation;
CO close-open operating cycle with the shortest possible close-open time such that the
circuit-breaker reaches the fully closed and latched position prior to opening;
t = 3 min for circuit-breakers for auto-reclosing. Alternative values of 15 s and 1 min can be
used;
t = 0,3 s for circuit-breakers for rapid auto-reclosing;
t' = 3 min. Alternative values of 15 s and 1 min can be used.
For some applications circuit-breakers can be used without auto-reclosing. For convenience of
testing these types of circuit-breakers can be tested with the operating sequence specified for
auto-reclosing.

Released for: Schneider Electric Hong Kong