Breaker Failure Protection 50Bf; Functional Description - Siemens SIPROTEC 4 Manual

2.17

Breaker Failure Protection 50BF

The breaker failure protection function monitors proper tripping of the relevant circuit breaker..

Functional Description

2.17.1
General
If after a programmable time delay, the circuit breaker has not opened, breaker failure protection issues a trip
signal to isolate the failure breaker by tripping other surrounding backup circuit breaker (see example in the
figure below).
[funktionsprinzip-svs-20061219, 1, en_US]
Figure 2-96
Initiation
The breaker failure protection function can be initiated by two different sources:
•
Trip signals of internal protective functions of the 7SJ80,
•
external trip signals via binary inputs (
For each of the two sources, a unique pickup message is generated, a unique time delay is initiated, and a
unique trip signal is generated. The setting values of current threshold and delay time apply to both sources.
Criteria
There are two criteria for breaker failure detection:
•
Check whether the current flow has effectively disappeared after a tripping command was issued,
•
Evaluate the circuit breaker's auxiliary contacts.
The criteria used to determine if the circuit breaker has operated are selectable and also depend on the protec-
tion function that initiated the breaker failure function. On tripping without fault current, e.g. via voltage
protection, the current below the threshold 50BF PICKUP is not a reliable indication of the proper func-
tioning of the circuit breaker. In such cases, pickup exclusively depends on the auxiliary contact criterion. In
protection functions based on the measurement of currents (including all short-circuit protection functions),
the current flow is a preferential criterion, i.e. it is given priority, as opposed to the auxiliary contacts. If
current flows above the set threshold or thresholds (enabled w/ 3I0>) are detected, the breaker failure
protection trips even if the auxiliary criterion indicates "Breaker Open".
SIPROTEC 4, 7SJ80, Manual
E50417-G1140-C343-A8, Edition 12.2017
Function principle of the breaker failure protection
>50BF ext SRC ).
Functions
2.17 Breaker Failure Protection 50BF
235