Functions
2.12 Breaker Failure Protection 50BF
SIPROTEC, 7SJ61, Manual
C53000-G1140-C210-1, Release date 02.2008
189
2.12.2 Setting Notes
General
Breaker failure protection is only effective and accessible if address 170 50BF is set to Enabled or enabled
w/ 3I0>. Setting Enabled considers the three phase currents for total current monitoring. Setting enabled
w/ 3I0> additionally evaluates the ground current or the negative sequence system when only one phase
current occurs.
If this function is not required, then Disabled is set. The function can be set to ON or OFF under address 7001
FCT 50BF.
Criteria
Address 7004 Chk BRK CONTACT establishes whether or not a breaker auxiliary contact is used, via a binary
input, as one of the criteria for pickup. If this address is set to ON, then the current criterion and/or the auxiliary
contact criterion apply. This setting must be selected if the circuit-breaker failure protection is started by func-
tions which do not always have a certain criterion for detection of an open circuit breaker.
Time Delay
The time delay is entered at address 7005 TRIP-Timer. This setting should be based on the maximum circuit
breaker operating time plus the dropout time of the current flow monitoring element plus a safety margin which
takes into consideration the tolerance of the time delay. Figure 2-66 illustrates the time sequences.
Figure 2-66 Time sequence example for normal clearance of a fault, and with circuit breaker failure
Pickup Values
The pickup value of the current flow monitoring is set under address 7006 50BF PICKUP, and the pickup value
of the ground current monitoring under address 7007 50BF PICKUP IE>. The threshold values must be set
at a level below the minimum fault current for which the total current monitoring must operate. A setting of 10%
below the minimum fault current for which breaker failure protection must operate is recommended. The pickup
value should not be set too low since otherwise there is a risk that transients in the current transformer second-
ary circuit may lead to extended dropout times if extremely high currents are switched off.
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