Setting Notes - Siemens SIPROTEC 7SK80 Manual
Motor protection
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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 the breaker auxiliary contacts connected via
binary inputs are to be used as a criterion for pickup. If this address is set to ON, then current criterion and/or
the auxiliary contact criterion apply. This setting must be selected if the circuit breaker failure protection is
started by functions, which do not always have a certain criterion for detection of an open circuit breaker, e.g.
voltage protection.
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 2-76 illustrates the time sequences.
Figure 2-76
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.
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
Time sequence example for normal clearance of a fault, and with circuit breaker failure
Functions
2.12 Breaker Failure Protection 50BF
203
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