ABB RELION REX640 Technical Manual page 751

1MRS759142 F
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.
IB
=
Figure 423: Operating characteristics of the stabilized earth-fault protection
function
Figure 424: Setting range of the operating characteristics for the stabilized
differential current principle of the earth-fault protection function
The
The differential current value required for tripping is constant at the stabilizing
current values 0.0 < IB/In < 1.0, where In is the nominal current, and the In in this
context refers to the nominal of the phase current inputs. When the stabilizing
REX640
Technical Manual
I A _ I B _ I C _
+ +
3
Operate value setting is used for defining the characteristics of the function.
Protection functions
(Equation 178)
751