ABB RELION REX640 Technical Manual page 793

1MRS759142 F
blocked by the waveform blocking functionality, the INT_BLKD output is activated
according to the phase information.
The phase angle difference between the two currents I_A1 and I_A2 is theoretically
180 electrical degrees for the external fault and 0 electrical degrees for the internal
fault conditions. If the phase angle difference is less than 50 electrical degrees or
if the biasing current drops below 30 percent of the differential current, a fault
has most likely occurred in the area protected by MPDIF. Then the internal blocking
signals (CT saturation and DC blocking) of the biased stage are inhibited.
Figure 450: Positive direction of current
Instantaneous high stage
The differential protection includes an unbiased instantaneous high stage. The
instantaneous stage operates and the OPR_HS output is activated when the
amplitude of the fundamental frequency component of the differential current
exceeds the set
differential current exceed 2.5 ·
to the maximum asymmetric short circuit current.
The OPERATE output is always activated when the OPR_HS output activates.
The internal blocking signals of the function block do not prevent the operation of
the instantaneous stage. When required, the operate signal due to instantaneous
operation can be blocked by the binary inputs BLK_OPR_HS or BLOCK.
REX640
Technical Manual
High operate value or when the instantaneous peak values of the
High operate value . The factor 2.5 (= 1.8 · √2) is due
Protection functions
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