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2.26
Breaker Failure Protection (ANSI 50BF)
The breaker failure protection function monitors proper switchoff of a circuit breaker.
In machine protection it is typically relates to the mains breaker.
2.26.1 Functional Description
Mode of Operation
The following two criteria are available for circuit breaker failure protection:
• Checking whether the current in all three phases undershoots a set threshold fol-
• Evaluation of the position of a circuit breaker auxiliary contact for protective func-
If the circuit breaker has not opened after a programmable time delay (breaker failure),
a higher-level circuit breaker can initiate disconnection (see the following example).
Figure 2-57
Initiation
The breaker failure protection function can be initiated by two different sources:
• Internal functions of the 7UM61, e.g. trip commands of protective functions or via
• external start commands e.g. via binary input.
Criteria
The two pickup criteria (current criterion, circuit breaker auxiliary contact) are OR-
combined. In case of a tripping without short circuit current, e.g. for voltage protection
on light load, the current is not a safe criterion for circuit breaker response. For this
reason pickup is also made possible using the auxiliary contact criterion.
The current criterion is fulfilled if at least one of the three phase currents exceeds a
parametrized threshold value (CIRC. BR. I>). The dropout is performed if all three
phase currents fall below 95 % of the pickup threshold value.
7UM61 Manual
C53000-G1176-C127-3
lowing a trip command,
tions where the current criterion is perhaps not representative, e.g. frequency pro-
tection, voltage protection, rotor earth fault protection.
Function Principle of the Breaker Failure Protection Function
CFC (internal logic functions),
2.26 Breaker Failure Protection (ANSI 50BF)
157
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