Functions
2.2 Overcurrent Protection 50, 51, 50N, 51N
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
87
The following must be observed:
• The value pairs should be entered in increasing sequence. If desired, fewer than 20 pairs can be entered.
In most cases, about 10 pairs is sufficient to define the characteristic accurately. A value pair which is not
used has to be made invalid by entering "
∞
” for the threshold! The user must ensure that the value pairs
produce a clear and constant characteristic .
The current values entered should be those from the following table, along with the matching times. Deviat-
ing values MofPU (multiples of PU-values) are rounded. This, however, will not be indicated.
Currents smaller than the current value of the smallest curve point will not lead to an extension of the tripping
time. The pickup curve (see Figure 2-17, right side) runs parallel to the current axis, up to the smallest
current value point.
Currents larger than the largest current value entered will not lead to a reduction of the tripping time. The
pickup curve (see Figure 2-17, right side) runs parallel to the current axis, beginning with the greatest current
value point.
Table 2-4
Preferential values of standardized currents for user-defined tripping curves
Figure 2-17
Using a user-defined curve
MofPU = 1 to 1.94
MofPU = 2 to 4.75
MofPU = 5 to 7.75
MofPU = 8 to 20
1.00
1.50
2.00
3.50
5.00
6.50
8.00
15.00
1.06
1.56
2.25
3.75
5.25
6.75
9.00
16.00
1.13
1.63
2.50
4.00
5.50
7.00
10.00
17.00
1.19
1.69
2.75
4.25
5.75
7.25
11.00
18.00
1.25
1.75
3.00
4.50
6.00
7.50
12.00
19.00
1.31
1.81
3.25
4.75
6.25
7.75
13.00
20.00
1.38
1.88
14.00
1.44
1.94
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