Parameter Value Description
2 channel
2-channel start is used if there is a risk that the circuit-breaker failure protec-
tion causes a tripping due to a faulty activation of the start binary input.
This is the case in the following situations:
a) The CBFP pickup value (threshold value) is set to less than the load
current.
b) There can be operating conditions under which the current flow is higher
than the pickup value.
To avoid a possible overfunction, Siemens recommends using the 2-channel
start.
1 channel
The 1-channel start must be used where only one control circuit of a binary
input is available for starting the CBFP.
Input Signals: >Start, >Release
The start and release input signals have a filtering time of 10 ms as default setting. If a transient control signal
to the binary inputs is to be expected due to the design of the external binary-input control circuits and due to
environmental conditions, the filtering time can be extended. This delays the start of the CBFP function.
Input Signals Description
>Start
The start input signal is linked with the tripping of the external protection
device (see Figure 6-256).
>Release
The release input signal is normally linked with the pickup of the external
protection device (see Figure 6-256). Another common configuration is the
parallel wiring of the external trip initiation to both binary inputs (start and
release).
Parameter: Supervision time for release signal
•
Default setting (_:111) Sup.time for release signl = 0.06 s
The setting depends on the external function which generates the release signal. If the pickup or tripping of
the external protection is used as release signal, the default setting can be kept. If it is ensured that the release
signal is always present before the starting signal, the time can be set to 0.
Parameter: Holding internal signal
•
Recommended setting value (_:105) Holding int. start signal = yes
Parameter Value
Description
yes
For an internal start, the starting signal is hold by default. The dropout of
the CBFP depends exclusively on the determination of the CB position.
This setting must be selected if it is not ensured that all 3 poles of the CB
have opened when the pickup signal of the protection function has a falling
edge.
Siemens recommends using this method as the standard method.
no
Holding of the starting signal can be disabled if it is ensured by the applica-
tion that the CB has reliably opened when the starting signal has a falling
edge, or if the CBFP is explicitly required to drop out when the starting
signal has a falling edge.
EXAMPLE
Holding internal starting signal (setting value: yes)
In the event of a 2-pole fault, only one contact of the CB opens. The fault current is thus reduced, and the
starting phase short-circuit protection drops out.
Protection and Automation Functions
6.41 Circuit-Breaker Failure Protection
SIPROTEC 5, Overcurrent Protection, Manual 845
C53000-G5040-C017-8, Edition 07.2017
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