6.7.6 Monitored data
Table 71: CCRBRF (50BF) Monitored data
Name
Type Values (Range) Unit Description
I_A REAL - A Measured current in phase A
I_B REAL - A Measured current in phase B
I_C REAL - A Measured current in phase C
IN REAL - A Measured residual current
6.7.7 Operation principle
Breaker failure protection, 3-phase activation and output CCRBRF (50BF) is initiated
from protection trip command, either from protection functions within the IED or from
external protection devices.
The initiate signal is general for all three phases. A re-trip attempt can be made after a set
time delay. The re-trip function can be done with or without CB position check based on
current and/or contact evaluation. With the current check the re-trip is only performed if
the current through the circuit breaker is larger than the operate current level. With contact
check the re-trip is only performed if breaker is indicated as closed.
The initiate signal can be an internal or external protection trip signal. This signal will
initiate the back-up trip timer. If the opening of the breaker is successful this is detected
by the function, by detection of either low current through RMS evaluation and a special
adapted current algorithm or by open contact indication. The special algorithm enables a
very fast detection of successful breaker opening, that is, fast resetting of the current
measurement. If the current and/or contact detection has not detected breaker opening
before the back-up timer has run its time a back-up trip is initiated.
Further the following possibilities are available:
• In the current detection it is possible to use three different options: 1 out of 3 where
it is sufficient to detect failure to open (high current) in one pole, 1 out of 4 where it
is sufficient to detect failure to open (high current) in one pole or high residual current
and 2 out of 4 where at least two current (phase current and/or residual current) shall
be high for breaker failure detection.
• The current detection level for the residual current can be set different from the setting
of phase current detection.
• Back-up trip is always made with current or contact check. It is possible to have this
option activated for small load currents only.
1MRK 511 287-UUS A Section 6
Current protection
139
Technical manual
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