Functions
226
7UM62 Manual
C53000-G1176-C149-3
The current criterion is fulfilled if at least one of the three phase currents exceeds a
parameterized threshold value (
). The dropout is performed if all three
phase currents fall below 95 % of the pickup threshold value.
If the binary input of the circuit breaker auxiliary contact is inactive, only the current
criterion is effective and the breaker failure protection cannot become active with a
tripping signal if the current is below the
threshold.
Two-Channel
Feature
To protect against nuisance tripping due to excessive contact bounce, a stabilization
of the binary inputs for external trip signals takes place. This external signal must be
present during the entire period of the delay time. Otherwise, the timer is reset and no
tripping signal is issued. A redundant binary input “>ext.start2 B/F” is linked to further
enhance the security against unwanted operation. This means that no initiation is
possible unless both binary inputs are activated. The two-channel feature is also
effective for an”internal” initiation.
Logic
If the breaker failure protection has picked up, a corresponding message is
transmitted and a parameterized time delay starts. If the pickup criteria are still fulfilled
on expiration of this time, a redundant source evaluation before fault clearing is
initiated via a further AND link by means of a superior circuit breaker.
A pickup drops off and no trip command is produced by the breaker failure protection if
−
an internal start condition (Output relay BO12 or via CFC) or “
”
or “
” causing the pickup drop off.
−
a tripping signal of the protective functions still exists, whereas the current criterion
and the auxiliary contact criterion drop out.
Figure 2-109 illustrates the logic diagram of the breaker failure protection. The overall
breaker failure protection can be switched on or off via parameters and also blocked
dynamically via binary inputs.
