Application Guide - NP900 Series
106 (504
)
A996A
phases measurement values are recorded event the harmonic is measured only in one
phase.
3.2.9
C
IRCUIT BREAKER FAILURE PROTECTION
(CBFP)
(50BF)
Circuit breaker failure protection (CBFP) function is used for monitoring the circuit breaker
operation after it has been tripped. CBFP function can be used for Retrip to the failing
breaker and if the Retrip fails the upstream breaker can be tripped by using CBFP output.
Retrip functionality can be disabled if the breaker does not have two open coils.
CBFP function can be triggered from overcurrent (phases and residual), digital output
monitor, digital signal or combination of these mentioned triggers.
In current dependent mode CBFP function constantly measures phase current
magnitudes and selected residual current. In signal dependent mode any of the IED
binary signal can be used for triggering the CBFP. In binary output dependent mode
CBFP monitors selected output relay control signal status. Blocking signal and setting
group selection controls the operating characteristics of the function during normal
operation.
Outputs of the function are CBFP START, RETRIP, CBFP ACT and BLOCKED signals.
Setting parameters are static inputs for the function which are changed only by user input
in the setup phase of the function. CBFP function utilizes total of eight separate setting
groups which can be selected from one common source. Also the operating mode of the
CBFP can be changed by setting group selection.
The operational logic consists of input magnitude processing, threshold comparator, block
signal check, time delay characteristics and output processing.
Inputs for the function are setting parameters and measured and pre-processed current
magnitudes and binary input and output signals. Function output signals can be used for
direct IO controlling and also for user logic programming. The function registers its
operation into 12 last time-stamped registers and also generates general time stamped
ON/OFF events to the common event buffer from each of the two output signal. Time
stamp resolution is 1ms. Function provides also cumulative counters for RETRIP, CBFP,
CBFP START and BLOCKED events.
In the following figure is presented the simplified function block diagram of the CBFP
function.
