ABB 615 series Technical Manual page 500

Section 4
Protection functions
494
The stabilized stage provides both DT and IDMT characteristics that are used for time
selective protection against faults which are not covered by the instantaneous stage. The
impedance of the line is typically an order of magnitude lower than the transformer
impedance providing significantly higher fault currents when the fault is located on the
line.
RED 615
400A/1
33kV

1 1 . 500 kVA

I
F
 
3 33 kV . 0
 
96 . 23 A

I * 1A
 

400 A
 
GUID-F9600D18-75B9-4EA5-8F9B-656FCB1FC938 V2 EN
Figure 245: 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.
500kVA
Z=10%

96 . 23 A
10
 
. 0 24 A 24 %
1MAC059074-MB A
RED 615
400A/1
615 series ANSI
Technical Manual