This is the Rated Operating Sequence (Duty Cycle) of the circuit breaker. Which denotes the sequence of opening and closing operations which the circuit breaker can perform under specified conditions. The operating mechanism experinces sever stress during the auto-reclosure duty; however, the circuit breaker should be able to perform the operating sequence as follows:
O-t-CO-T-CO
where,
O = opening operation
t = time required for circuit breaker to be ready to receive closing order from auto-reclosure relay (0.3 s to be used for rapid reclosure), (3 min not to be used for rapid reclosure).
CO = close operation followed by open operations
T = time required by the circuit breaker, insulating media for regeneration and operating mechanism (3 min)
CO = close operation followed by open operations
