The current transformer ratio mismatch between the phase current
transformer and neutral current transformer (residual current in the analog
input settings) is taken into account by the function with the properly set
analog input setting values.
During a ground fault in the protected area, the currents ΣI and IG are directed towards the
protected area. The factor cosφ is 1 when the phase difference of the residual current and
the neutral current is 180 degrees, that is, when the currents are in opposite direction at the
ground faults within the protected area. Similarly, ID_COSPHI is specified to be 0 when
the phase difference between the residual current and the neutral current is less than 90
degrees in situations where there is no ground fault in the protected area. Thus tripping is
possible only when the phase difference between the residual current and the neutral
current is above 90 degrees.
The stabilizing current IB used by the stabilizing current principle is calculated as an
average of the phase currents in the windings to be protected. The value is available in the
monitored data view.
IB
I
A
I
B
I
C
=
+
+
_
_
_
3
GUID-E162EE11-DEDF-49BA-B60F-E22ECF1ACAE8 V2 EN
(Equation 92)
0.0
0.5
1.0
1.5
0.0
1.0
2.0
3.0
IB/In
ID_COSPHI/ In
ID
IB
TRIPPING
NON TRIPPING
Trip value
GUID-9D592151-7598-479B-9285-7FB7C09F0FAB-ANSI V1 EN
Figure 268:
Operating characteristics of the stabilized ground-fault protection
function
Section 4
1MAC059074-MB A
Protection functions
540
615 series ANSI
Technical Manual
Summary of Contents for Relion 615 series
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