Siemens siprotec SJ62 User Manual page 262

Criteria
Time Delay
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
Address 7004 Chk BRK CONTACT establishes whether or not a breaker auxiliary
contact is used, via a binary input, as criteria for pickup. If this address is set to ON,
then current criterion and/or the auxiliary contact criterion apply. This is important if the
current is smaller than the configured current threshold (BkrClosed I MIN, address
212) despite of the fact that the circuit breaker is closed. The latter may apply if pro-
tective tripping was caused by a voltage measurement (e.g. 64 TRIP, 59–1 TRIP / 59–
2 TRIP, 27–1 TRIP / 27–2 TRIP). If these protective functions issue a trip command,
the criteria for current and auxiliary contacts are linked by a logical OR operation.
Without the auxiliary contact criterion the circuit breaker failure protection would not
be able to take effect in this case.
For all other protection functions the current and auxiliary contact criteria are com-
bined by logical AND as long as the address Chk BRK CONTACT is set to ON.
The pickup threshold BkrClosed I MIN setting of integrated current supervision
(address 212) refers to all three phases. The threshold value must be set at a level
below the minimum fault current for which the function 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, otherwise, the danger exists that switching
off transients in the current transformer secondary circuit could lead to extended drop
out times under conditions of extremely high current to be switched off.
In addition, it should be noted that other protection functions depend on the pickup
value BkrClosed I MIN as well (e.g. voltage protection, overload protection, and
restart inhibit for motors).
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. In case of an external start, the set time delay is
reduced automatically by 10 ms in order to compensate the residual time of the exter-
nal start. Figure 2-89 illustrates the time sequences.
Figure 2-89 Timing for a Typical Breaker Failure Scenario
2.16 Breaker Failure Protection 50BF
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