•
If the minimum fault-clarification time has top priority, Siemens recommends setting the time to 0. This
setting causes initiation of the retrip immediately upon the start. The drawback is that a defect of the 1st
trip circuit is not detected.
•
With a small time delay of, for instance, 50 ms, the defect of the 1st trip circuit can be detected based on
the evaluation of the fault record.
•
With a long time delay which reliably ensures the dropout of the CBFP with the CB open, the rising edge
indication of the trip repeat Retrip T1 is a sure signal for a fault in the 1st trip circuit. The following
example shows how this time is determined.
EXAMPLE
Determining the T1 Time that Reliably Ensures the Dropout of the CBFP with the CB Open:
Time of binary device output
(when tripping is caused by the device-internal
protection)
5 ms
CB inherent time up to current interruption 2 periods (assumed rated frequency = 50 Hz)
Dropout time of CBFP function 1 period
Subtotal 65 ms
Security Factor 2
Total (time T1) 130 ms
Parameter: Delay T2 for 3-pole trip
•
Default setting (_:110) Delay T2 for 3-pole trip = 0.13 s
This setting has to ensure that after opening of the local CB the function drops out reliably and that backup
tripping is avoided under all circumstances. The setting depends on the parameter Retrip after T1.
If T2 is started afterT1, there is no need to consider the time T1 for the setting of T2.
EXAMPLE
Determining the T2 Time that Reliably Ensures the Dropout of the CBFP with the CB Open:
Time of binary device output
(when tripping is caused by the device-internal
protection)
5 ms
CB inherent time up to current interruption 2 periods (assumed rated frequency = 50 Hz)
Dropout time of CBFP function 1 period
Subtotal 65 ms
Security Factor 2
Total (time T2) 130 ms
If T1 and T2 are started in parallel, take into account the time T1 for the setting of T2.
EXAMPLE
Simultaneous start of T2 and T1
Time for a reliable dropout after the local CB has
opened
130 ms
Setting of T1 50 ms
Total (= T2) 180 ms
Protection and Automation Functions
6.41 Circuit-Breaker Failure Protection
SIPROTEC 5, Overcurrent Protection, Manual 849
C53000-G5040-C017-8, Edition 07.2017
To Next Page
Loading...
