Siemens 6MD85, Manual

Page: 532 / 1256

Parameter Value Description
yes
For an internal start, the starting signal is hold. 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. If the CBFP is explicitly required to drop out when the starting signal
has a falling edge, holding of the starting signal can also be disabled.
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.
Parameter: Holding ext. start signal
•
Recommended setting value
(_:106) Holding ext. start signal
=
no
Parameter Value Description
no
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.
yes
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.
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.
i
i
NOTE
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
sc,min
•
Recommended setting value
(_:101) Threshold sensitive
=
approx. 0.50 I
sc,min
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
sc,min
).
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
sc,min
). There can also be values which are noticeably below the rated or load current.
Protection and Automation Functions
7.1 Circuit-Breaker Failure Protection
532 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017