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Protection and Automation Functions
6.41 Circuit-Breaker Failure Protection
Parameter: Holding ext. start signal
•
Recommended setting value (_:106) Holding ext. start signal = no
Parameter Value
no
yes
EXAMPLE
Holding external starting signal (setting value: yes)
The function is started from the opposite end via an auxiliary device for command transmission. This device
generates only a signal pulse.
NOTE
i
i
Siemens would like to point out that, with a hold signal, the CBFP generates a trip signal each time a
starting pulse is received and the current flow is high enough. Remember this particularly in the case of an
external start.
Parameter: Threshold phase current/Threshold sensitive
•
Recommended setting value (_:102) Threshold phase current = approx. 0.50 I
•
Recommended setting value (_:101) Threshold sensitive = approx. 0.50 I
In order to ensure that the disconnection of the fault is promptly detected and the function can drop out
quickly, Siemens recommends setting both thresholds to half the minimum short-circuit current (I
If – depending on the neutral-point treatment and/or load conditions – ground faults lead to relatively low
fault currents, a sensitive setting of the parameter Threshold sensitive must be selected according to
the rule (0.5 I
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Input Signal: >Threshold sensitive
In order to ensure that the function picks up reliably in all switch positions of the power-supply system (exam-
ples: opposite end of line open, switching onto a ground fault), the setting of the parameter Threshold
sensitive can be applied dynamically to all currents - including phase currents – in the presence of ground
faults. For this purpose, the binary signal >Threshold sensitive must be activated. This can be done via a
device-internal function for ground-fault detection (if provided in the device), for example, using Overvoltage
protection with zero-sequence voltage. In this case, the pickup of the V0> function must be linked with the
binary signal. Alternatively, the signal can be coupled from a separate device for sensitive ground-fault detec-
tion via a binary input.
Parameter: Circuit-breaker auxiliary contact criterion allowed for protection
•
Recommended setting value (_:103) CB aux.cont. crit. allowed = no
Parameter Value
no
846
Description
The CBFP drops out when the external starting signal has a falling edge. This
setting prevents the CBFP from generating a tripping signal when an
unwanted pulse is received at the binary input and the current flow is high
enough.
Siemens recommends using this method as the standard method.
You can hold the starting signal if it is not ensured that the circuit breaker is
open when the external starting signal has a falling edge.
). There can also be values which are noticeably below the rated or load current.
Description
If sufficient current flow is ensured under all conditions with the CB closed,
Siemens recommends not to permit the auxiliary contacts as a further crite-
rion for determining the CB position, because measurement based on the
current flow is the most reliable criterion.
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SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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).
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