ABB RELION REX640 Technical Manual page 792

Protection functions
Slope section
Slope section
The end of the first section
range of 0 to 100 percent (or % I
section 2 can be set within the range of 100 percent to 300 percent (or % I
The slope of the operating characteristic for the function block varies in different
parts of the range.
In section 1, where 0.0 < I
tripping is constant. The value of the differential current is the same as the
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
of the setting
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
section 2 setting allows for CT errors.
In section 3, where I
set by
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
I
doperate
For a stabilizing current higher than
I
doperate
For higher stabilizing current values exceeding
I I Lowoperate value
[% ]
=
d operate r
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
792
I
d 2
2 100 %
= ⋅
I
b 2
I
d 3
3 100 %
= ⋅
I
b 3
End section 1 can be set at a desired point within the
/I
b
End section 1 < I
Slope section 2 . In this section, variations in End section 2 affect the
End section 2 , the slope of the characteristic can be
/I >
b n
Slope section 3 that defines the increase in the differential current to the
I Set Lowoperate value
[% ] =
r
[% ] I Lowoperate value
=
r
End section End section
( 2
+ −
). Accordingly, the end of the second section
r
End section 1 , the differential current required for
<
n
End section 2 , is called the influence area
/I <
b n
End section 1
End section 1 but lower than End section 2
( [% ] I Ir End section
+ −
b
End section 2
S l l ope section
1 ) 2
⋅ +
1MRS759142 F
(Equation 204)
(Equation 205)
(Equation 206)
1 ) Slope s s ection 2
⋅
(Equation 207)
I I End section
( [% ] 2 )
− ⋅
b r
(Equation 208)
Technical Manual
End
).
r
Low
End
Slope section
3
REX640