2 Functions
122
7ST6 Manual
E50417-G1176-C251-A3
2.11.2 Setting Notes
The inrush restraint is only necessary if the device is to be used on transformer
feeders or on overhead contact lines in an auto-transformer system. Even in those ap-
plications, the inrush restraint is only needed for protection functions which the inrush
current might cause to trip.
Such protection functions are the time overcurrent protection and the distance protec-
tion.
With the parameters
Inrush DIS >=Z2
(address
2301
),
Inrush O/C
(address
2302
) and
Inrush O/C BU
(address
2303
), the inrush restraint can be set for each
protection function separately to
YES
(effective) or
NO
(inrush restraint ineffective). If
the inrush restraint has been disabled for all functions, the following parameters are of
no consequence.
For the recognition of the inrush current, the portion of second harmonic current
content referred to the fundamental current component can be set in address
2305
2nd HARM.BLOCK
. Above this threshold the inrush blocking is effective. The preset
value (15 %) should be sufficient in most cases. Lower values imply higher sensitivity
of the inrush blocking (smaller portion of second harmonic current results in blocking).
In applications on transformer feeders or overhead contact lines that are terminated
on transformers it may be assumed that, if very large currents occur, a short circuit has
occurred in front of the transformer. In the event of such large currents, the inrush re-
straint is inhibited. This threshold value which is set in the address
2306
Imax
InrushRest
, should be larger than the maximum expected inrush current (RMS
value).
In the parameter
2307
SI Time INRUSH
the action time of the inrush detection can
be specified. When this time has elapsed, the blocking of protection functions by the
inrush restraint feature is reset, regardless of the second harmonics content of the cur-
rent.
The indication
„INRUSH detected“
signals that an inrush has been detected. This
indication can also be used to block external protection devices during the inrush
phase if these external devices do not have an inrush restraint feature of their own.
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