For inrush-current detection, 2 methods working in parallel are used:
•
Component of the 2nd harmonic relative to the fundamental component in the differential current
(I
2nd harm
/I
1st harm
)
As Figure 7-47 also shows, the 2nd harmonic is clearly pronounced in the inrush current. If the share of
the 2nd harmonic exceeds the set threshold value (parameter: 2nd harmonic content), a phase-
segregated blocking occurs. The harmonics develop differently in the different phases. If exceeding of
the 2nd harmonic is detected in a phase, it may be necessary to block all phases simultaneously. This
blocking must be limited with regard to time and is controlled by the parameter Crossblock. time
2nd har.. The correct positioning of the filter windows is controlled by the internal pickup.
If you want only one method to be active, the other method can be changed to inactive. For this, parameter
Blocking with 2. harmonic = no is used.
[scinrush-120120-01.tif, 1, en_US]
Figure 7-47 Inrush Current with Pronounced Flat Areas
Figure 7-48 shows the logical input and output signals.
[loblkcap-290414-01, 1, en_US]
Figure 7-48 Logic Inrush-Current Detection
Capacitor Bank Protection
7.8 Differential Protection for Capacitor Banks
1046 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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