Basler Electric BE1-BPR - Manual (Page 35)

9272000990 Rev J BE1-BPR Application 2-11
Breaker Failure Protection with Pre-Insertion Resistors
Breakers that will be exposed to fault currents above the maximum rated interrupting capacity are
normally equipped with pre-insertion resistors. Pre-insertion resistors are mechanically placed in series
with the breaker interrupting contacts when the breaker opens. This reduces the current magnitude until
the fault is cleared a cycle or more later.
Typically, the BE1-BPR fault detector is set to pickup below the minimum pre-insertion resistor current
level to insure that the breaker has opened and the fault cleared. Sometimes, system stability requires
faster clearing times and closer margins on breaker failure timing. The BE1-BPR can be configured to
provide a faster BF clearing time for an initial higher fault current level, and slower BF clearing time for
lower level fault currents that are limited by the pre-insertion resistors.
This adaptive breaker failure logic can be configured by making use of the additional fault detectors and
timers available in the BE1-BPR. One BF delay timer would be set to the maximum time allowed for the
higher fault current level to be cleared and maintain system stability. The output would be ANDed with a
fault detector set to detect this higher fault current level. This fault detector will drop out when the current
is reduced because the pre-insertion resistor is inserted. Another BF delay timer would be set for a longer
time based on the maximum time allowed for the lower current level fault to be cleared. This timer output
would be ANDed with a different fault detector set to pickup on pre-insertion resistor current levels. The
output of both AND gates would be ORed so that either one would drive the BF output.
This logic provides improved security and protection for breaker failure by providing two timing margins
and two different fault current levels. See BFRES logic in BE1-BPR Custom Application Schemes,
Section 5, Programmable Logic, for a specific application example.
Note that the preprogrammed breaker failure logic schemes in the BE1-BPR relay do not provide breaker
failure protection for the single-pole tripping of breakers with pre-insertion resistors. This is because the
fault detector level would have to be set at a level that is less than the normal load current. Therefore, the
phase fault detector would stay picked up because of the load current on the non-faulted phases.
Breaker Contact Duty Log
Breaker contact duty log is a diagnostic feature to monitor the number of times a breaker has operated
and accumulate the total contact duty or wear based on the current interrupted. The log is contained in
the form of a ∑I 2 t for each pole of the breaker. The total is reported as a percent of maximum for simplicity.
If the total exceeds the maximum programmed for any breaker pole, an internal diagnostic flag, Figure
2-14 becomes TRUE. In the preprogrammed logic schemes, the programmable diagnostic output (O14 or
O15) can be enabled using the PDIAG command to turn on the Alarm output to signal the operator that
maintenance is needed.
See Section 4, Functional Description, for a detailed functional description on how to program the duty log
diagnostic feature.
Figure 2-14. Breaker Contact Duty Log Circuits