ABB RELION REX640 Technical Manual page 674

Protection functions
400A/1

I
L

I

Figure 383: Influence of the tapped transformer load current to the stabilized low
stage setting
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.
400A/1
33kV
Figure 384: 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
674
RED 615
PROTECTED ZONE
33kV
500kVA
500 kVA

. 8 75 A

3 33 kV
 
. 8 75 A

* 1A . 0 02 A
 
400 A
 
RED 615
500kVA
Z=10%

1 1 . 500 kVA

I
F
 
3 33 kV . 0 10
 
96 . 23 A
 
I * 1A
 

400 A
 

2 %

96 . 23 A

. 0 24 A 24 %
1MRS759142 F
RED 615
400A/1
RED 615
400A/1
Technical Manual
REX640