failure. 1 out of 3 means that at least one current of the three-phase currents shall be
high to indicate breaker failure. 1 out of 4 means that at least one current of the three-
phase currents or the residual current shall be high to indicate breaker failure. In most
applications 1 out of 3 is sufficient. For Contact operation means back-up trip is done
when circuit breaker is closed (breaker position is used).
IP>: Current level for detection of breaker failure, set in % of IBase. This parameter
should be set so that faults with small fault current can be detected. The setting can be
chosen in accordance with the most sensitive protection function to start the breaker
failure protection. Typical setting is 10% of IBase.
I>BlkCont: If any contact based detection of breaker failure is used this function can
be blocked if any phase current is larger than this setting level. If the FunctionMode is
set Current&Contact breaker failure for high current faults are safely detected by the
current measurement function. To increase security the contact based function should
be disabled for high currents. The setting can be given within the range 5 – 200% of
IBase.
IN>: Residual current level for detection of breaker failure set in % of IBase. In high
impedance earthed systems the residual current at phase- to-earth faults are normally
much smaller than the short circuit currents. In order to detect breaker failure at single-
phase-earth faults in these systems it is necessary to measure the residual current
separately. Also in effectively earthed systems the setting of the earth-fault current
protection can be chosen to relatively low current level. The BuTripMode is set 1 out
of 4. The current setting should be chosen in accordance to the setting of the sensitive
earth-fault protection. The setting can be given within the range 2 – 200 % of IBase.
t1: Time delay of the re-trip. The setting can be given within the range 0 – 60s in steps
of 0.001 s. Typical setting is 0 – 50ms.
t2: Time delay of the back-up trip. The choice of this setting is made as short as
possible at the same time as unwanted operation must be avoided. Typical setting is 90
– 200ms (also dependent of re-trip timer).
The minimum time delay for the re-trip can be estimated as:
_
2 1³ + + +
cbopen BFP reset margin
t t t t t
EQUATION1430 V1 EN (Equation 43)
where:
t
cbopen
is the maximum opening time for the circuit breaker
t
BFP_reset
is the maximum time for breaker failure protection to detect correct breaker function (the
current criteria reset)
t
margin
is a safety margin
1MRK 505 291-UEN A Section 6
Current protection
135
Application manual
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