Minimum Operate Currents - ABB Relion 670 Series Technical Reference Manual

Section 6
Impedance protection
6.3.3.5
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IEC08000437 V1 EN
Figure 109: Rotation of load characteristic for a fault between two phases
There is a gain in selectivity by using the same measurement as for the quadrilateral
characteristic since not all phase-to-phase loops will be fully affected by a fault
between two phases. It should also provide better fault resistive coverage in quadrant
one. The relative loss of fault resistive coverage in quadrant four should not be a
problem even for applications on series compensated lines.

Minimum operate currents

The operation of the Phase selection with load encroachment function (FDPSPDIS, 21)
is blocked if the magnitude of input currents falls below certain threshold values.
The phase-to-ground loop n is blocked if In<IMinPUPG, where In is the RMS value of
the current in phase n (A or B or C).
The phase-to-phase loop mn is blocked if (2·In<IMinPUPP).
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Technical reference manual