Breaker Failure Protection 50Bf; Description - Siemens siprotec SJ62 User Manual

2 Functions
2.16

Breaker Failure Protection 50BF

2.16.1 Description

General
Initiation
Criteria
257
The breaker failure protection function monitors the reaction of a circuit breaker to a
trip signal.
If after a programmable time delay, the circuit breaker has not opened, breaker failure
protection issues a trip signal via a superordinate circuit breaker (see Figure 2-87, as
an example).
Figure 2-87 Functional principle of the breaker failure protection function
The breaker failure protection function can be initiated by two different sources:
• Trip signals of internal protective functions of the 7SJ62/63/64,
• External trip signals via binary inputs („>50BF ext SRC").
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.
There are two criteria for breaker failure detection:
• Checking whether the actual current flow effectively disappeared after a tripping
command had been issued,
• Evaluate the circuit breaker auxiliary contact status.
The criteria used to determine if the circuit breaker has operated is selectable and
should depend on the protective function that initiated the breaker failure function.
When tripping without fault current, e.g. by voltage protection, the current is not a re-
liable indication as to whether the circuit breaker operated properly. In this case, the
position of the breaker auxiliary contact should be used to determine if the circuit
breaker properly operated. However, for protective functions that operate in response
to currents (i.e. all fault protection functions) both the current criterion and the criterion
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015