ABB RELION 620 Series Technical Manual page 555

1MRS757644 F
620 series
Technical Manual
operation criteria to maintain selectivity. A correct value for CT connection type is
determined by the connection polarities of the current transformer.
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 an earth fault in the protected area, the currents ΣI and Io 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 earth 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 earth 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.
I A _ I B _ I C _
+ +
IB
=
3
GUID-E162EE11-DEDF-49BA-B60F-E22ECF1ACAE8 V2 EN
GUID-9D592151-7598-479B-9285-7FB7C09F0FAB V1 EN
Figure 277: Operating characteristics of the stabilized earth-fault protection
function
Section 4
Protection functions
(Equation 82)
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