Siemens 6MD85, Manual

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Circuit-Breaker Failure Protection
Overview of Function
The Circuit-breaker failure protection function (ANSI 50BF) monitors the tripping of the associated circuit-
breaker (CB) and generates a backup trip signal if the circuit-breaker fails.
Starting with version V7.50, the previous function CB failure has been replaced with the new circuit-breaker
failure protection with an adaptive algorithm Adaptive CB failure protection. In this way, you achieve a
faster, more reliable detection of the opening of the circuit breaker in the event of complex signal histories.
The 2 functions are identical, with the exception of a slightly increased processor load, in terms of setting
options, logic and indications. Siemens recommends using the adaptive circuit-breaker failure protection and
avoiding mixing the protection types in one device. You can find additional information on the processor load
in DIGSI for each device under Device information in the Resource consumption tab.
Structure of the Function
The function Circuit-breaker failure protection (CBFP) can be used in the Circuit-breaker function group.
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Figure 7-1 Structure/Embedding of the Function
Figure 7-2 shows the functionalities and the function control of the function.
The start is initiated by the device-internal protection function or by an external protection. Along with the
start, the current-flow criterion or the circuit-breaker auxiliary contact criterion is used to check whether the
circuit breaker is closed. If the circuit breaker is closed, the function picks up and starts the time delay. During
the time delay, the system checks continuously whether the circuit breaker has opened. If this is the case, the
function drops out. If the circuit breaker is not opened, the function trips upon expiration of the time delay.
The following description elaborates on the detailed functionality of the individual function blocks.
7.1
7.1.1
7.1.2
Protection and Automation Functions
7.1 Circuit-Breaker Failure Protection
516 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017