In it simplest, all auto-reclose shots are initiated by protection trips. As a result, all trip times in the sequence are the same. This is why using protection trips may not be the optimal solution. Using protection start signals instead of protection trips for initiating shots shortens the trip times.
Example 1
- protection operate time = 0.5s
- Str 2 delay shot 1 = 0.05s
- Str 2 delay shot 2 = 60s
- Str 2 delay shot 3 = 60s
Operation in a permanent fault:
- Protection starts and activates the DEL_INIT 2 input.
- After 0.05 seconds, the first autoreclose shot is initiated. The function opens the circuit breaker: the OPEN_CB output activates. The total trip time is the protection start delay + 0.05 seconds + the time it takes to open the circuit breaker.
- After the first shot, the circuit breaker is reclosed and the protection starts again.
- Because the delay of the second shot is 60 seconds, the protection is faster and trips after the set operation time, activating the INIT 2 input. The second shot is initiated.
- After the second shot, the circuit breaker is reclosed and the protection starts again.
- Because the delay of the second shot is 60 seconds, the protection is faster and trips after the set operation time. No further shots are programmed after the final trip. The function is in lockout and the sequence is considered unsuccessful.
Example 2
The delays can be used also for fast final trip. The conditions are the same as in Example 1, with the exception of Str 2 delay shot 3 = 0.10 seconds.
The operation in a permanent fault is the same as in Example 1, except that after the second shot when the protection starts again, Str 2 delay shot 3 elapses before the protection operate time and the final trip follows. The total trip time is the protection start delay + 0.10 seconds + the time it takes to open the circuit breaker.