Slope section
I
I
d
b
2 100
2
2
= ⋅ %
(Equation 204)
Slope section
I
I
d
b
3 100
3
3
= ⋅ %
(Equation 205)
The end of the first section
End section 1
can be set at a desired point within the
range of 0 to 100 percent (or % I
r
). Accordingly, the end of the second section
End
section 2
can be set within the range of 100 percent to 300 percent (or % I
r
).
The slope of the operating characteristic for the function block varies in different
parts of the range.
In section 1, where 0.0 < I
b
/I
n
<
End section 1
, the differential current required for
tripping is constant. The value of the differential current is the same as the
Low
operate value
setting selected for the function block. The
Low operate value
setting
allows for small inaccuracies of the current transformers but it can also be used to
influence the overall level of the operating characteristic.
Section 2, where
End section 1
< I
b
/I
n
<
End section 2
, is called the influence area
of the setting
Slope section 2
. In this section, variations in
End section 2
affect the
slope of the characteristic, that is, how big the change in the differential current
required for tripping is in comparison to the change in the load current. The
End
section 2
setting allows for CT errors.
In section 3, where I
b
/I
n
>
End section 2
, the slope of the characteristic can be
set by
Slope section 3
that defines the increase in the differential current to the
corresponding increase in the biasing current.
The required differential current for tripping at a certain stabilizing current level can
be calculated using the formulae:
For a stabilizing current lower than
End section 1
I I Set Lowoperate value
doperate r
[% ] =
(Equation 206)
For a stabilizing current higher than
End section 1
but lower than
End section 2
I I Lowoperate value I Ir End section Slope
doperate r b
[% ] ( [% ] )= + − ⋅1 ssection 2
(Equation 207)
For higher stabilizing current values exceeding
End section 2
I I Lowoperate value End section End section S
d operate r
[% ] ( )= + − ⋅2 1 llope section I I End section Slope section
b r
2 2 3+ − ⋅( [% ] )
(Equation 208)
When the differential current exceeds the operating value determined by the
operating characteristics, the OPR_LS output is activated. The OPERATE output is
always activated when the OPR_LS output activates.
The operate signal due to the biased stage can be blocked by the activation of the
BLK_OPR_LS or BLOCK input. Also, when the operation of the biased low stage is
Protection functions
1MRS759142 F
792 REX640
Technical Manual
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