100
200
300
100 200 300 400 500
Low
operate
value
Slope
section
2
End
section
2
Curve
1
2
3
50 %Ir
20 %Ir
50 % 100 %Ir
30 % 150 %Ir
5 %Ir 10 % 500 %Ir
Curve 1
Curve 2 ( Default settings )
Curve 3
I
d
[%I
r
]
I
d
[%I
r
]
Figure 412: Setting range for biased low stage
If the biasing current is small compared to the differential current or if the phase
angle between the currents of two windings with the highest phase current is
close to zero (normally, the phase difference is 180 degrees) or the phase angle
between the compared phase currents (in case of two-winding transformer) is close
to zero, a fault has most certainly occurred in the area protected by the differential
protection relay. The internal blocking signals of the biased stage are inhibited.
The operation of the differential protection is based on the fundamental frequency
components. The operation is accurate and stable: the DC component and
harmonics of the current do not cause unwanted operations.
Instantaneous high stage
Instantaneous high stage can be enabled or disabled with the
Enable high set
setting. The corresponding parameter values are "True" and "False".
The operation of Instantaneous high stage is not biased. 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
operation value
High operate value
or when the instantaneous value of the
differential current exceeds 2.5 ·
High operate value
. The value 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 if the phase
angle between the currents of the two windings with the highest phase current is
close to zero (normally, the phase difference is 180 degrees) or the phase angle
between the compared phase currents (in case of a two-winding transformer)
is close to zero, a fault has occurred in the area protected by the differential
protection. The operating value set for the instantaneous stage is automatically
halved and the internal blocking signals of the biased stage are inhibited.
Protection functions
1MRS759142 F
728 REX640
Technical Manual
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