ABB RELION 620 Series Technical Manual page 416

Section 4
Protection functions
410
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 87M. Then the internal blocking signals (CT saturation and DC
blocking) of the biased stage are inhibited.
GUID-D401D103-BD7C-4096-986F-578925ADB1CC V1 EN
Figure 186: Positive direction of current
Unrestrained differential (high stage)
The differential protection includes an unbiased instantaneous high stage. The
instantaneous stage trips and the OPR_HS output is activated when the amplitude of the
fundamental frequency component of the differential current exceeds the set High operate
value or when the instantaneous peak values of the differential current exceed 2.5 · High
operate value. The factor 2.5 (= 1.8 · √2) is due to the maximum asymmetric short circuit
current.
The TRIP 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 trip signal due to instantaneous operation can be
blocked by the binary inputs BLK_OPR_HS or BLOCK.
1MAC504801-IB E
620 series ANSI
Technical Manual