the phase difference is 180 degrees), a fault has most likely occurred in the area protected
by 87T. Then the internal blocking signals of the biased stage are inhibited.
Instantaneous high stage
The instantaneous high stage operation can be enabled and disabled with the Enable high
set setting. The corresponding parameter values are "TRUE" and "FALSE."
The operation of the instantaneous high stage is not biased. The instantaneous stage trips
and the output OPR_HS is activated when the amplitude of the fundamental frequency
component of the differential current exceeds the set High trip value or when the
instantaneous value of the differential current exceeds 2.5 times the value of High trip
value. The factor 2.5 (=1.8 × √2) is due to the maximum asymmetric short circuit current.
If the biasing current is small compared to the differential current or the phase angle
between the winding 1 and winding 2 phase currents is close to zero (in a normal situation,
the phase difference is 180 degrees), a fault has occurred in the area protected by 87T.
Then the trip value set for the instantaneous stage is automatically halved and the internal
blocking signals of the biased stage are inhibited.
I_D
I_B
Slope
section 2
Low trip value
TRIP
AREA (LS)
NON-TRIP
AREA
End section 1
High trip value
TRIP
AREA (HS)
Slope
section 3
End section 2
GUID-8B8EC6FC-DF75-4674-808B-7B4C68E9F3E8-ANSI V1 EN
Figure 255: Operating characteristics of the protection. (LS) stands for the biased low
stage and (HS) for the instantaneous high stage
The TRIP output is activated always when the OPR_HS output activates.
The internal blocking signals of the differential function do not prevent the trip signal of
the instantaneous differential current stage. When required, the trip outputs of the
instantaneous high stage can be blocked by the BLK_OPR_HS and BLOCK external
control signals.
1MAC059074-MB A Section 4
Protection functions
615 series ANSI 513
Technical Manual
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