Measurands
Within the protection stage, the compensated and the non-compensated unbalanced currents are available.
Use the parameter Measured value to select one of the 2 values. Both values are displayed as measured
values of the function at the function stage.
Pickup, Tripping Delay
If the selected measurand in one of the phase measuring element exceeds the threshold, the stage picks up.
The pickup starts a tripping time delay, and a fault-location information is issued. More information can be
found in this chapter under Fault-Location Information, Page 995. If the threshold is exceeded during the
entire tripping delay, a phase-selective operate indication is issued.
Please note that, when using the compensated measurands as well as the automatic compensation, the
currently measured current unbalance (that resulted in the threshold being exceeded) is gradually compen-
sated. This means that even in case of a constantly existing unbalance in the primary system, the compen-
sated measurand becomes gradually lower and may therefore fall below the threshold again at some time.
The timing depends on by how much the threshold is exceeded.
For this reason and under those conditions, long time delays must not be set, see also chapter 7.4.4.2 Applica-
tion and Setting Notes.
This effect does not occur if manual compensation or the non-compensated measurand is used.
Blocking While Charging
In order to prevent pickup as a consequence of the charging process, the I> stage is implicitly blocked in a
phase-selective way for 250 ms by setting
I
unbal.,comp.
to 0 A, after capacitor energizing has been detected.
Blocking only takes place if the stage operates with compensated unbalanced values.
Fault-Location Information
When picking up, the stage provides information about the faulty group of the capacitor bank. If the location
can be safely determined, the corresponding indication
Fault position group 1
or
Fault position
group 2
is issued.
Both indications also contain the information about the faulty phase. If the capacitor is implemented as an H
connection, the following definition is assumed:
Capacitor Bank Protection
7.4 Current-Unbalance Protection for Capacitors, 3-Phase
SIPROTEC 5, Overcurrent Protection, Manual 995
C53000-G5040-C017-8, Edition 07.2017
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