ABB RELION 620 Series Technical Manual page 501

1MRS757644 F
620 series
Technical Manual
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.
GUID-D401D103-BD7C-4096-986F-578925ADB1CC V1 EN
Figure 248: 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
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 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.
Section 4
Protection functions
495