ABB RED615 Technical Manual page 384

Section 4
Protection functions
378
transformer impedance providing significantly higher fault currents when the fault
is located on the line.
GUID-F9600D18-75B9-4EA5-8F9B-656FCB1FC938 V1 EN
Figure 202: Influence of the short circuit current at LV side of the tapped
transformer to the differential current
Detection of the inrush current during transformer start-up
When the line is energized, the transformer magnetization inrush current is seen as
differential current by the line differential protection and may cause malfunction of
the protection if not taken into account. The inrush situation may only be detected
on one end but the differential current is always seen on both ends. The inrush
current includes high order harmonic components which can be detected and used
as the blocking criteria for the stabilized stage. The inrush detection information is
changed between two ends so that fast and safe blocking of the stabilized stage can
be issued on both ends.
1YHT530004D05 D
615 series
Technical Manual