2.8 Earth Fault Protection in Earthed Systems (optional)
211
7SD5 Manual
C53000-G1176-C169-1
Inverse Time Over-
current Stage with
Logarithmic–
Inverse Character-
istic
The inverse logarithmic characteristic differs from the other inverse characteristics
mainly by the fact that the shape of the curve can be influenced by a number of pa-
rameters. The slope and a time shift 3I0p MaxT-DELAY which directly affect the
curve, can be changed. The characteristics are shown in the Technical Data.
Figure 2-90 shows the logic diagram. In addition to the curve parameters, a minimum
time 3I0p MinT-DELAY can be determined; below this time no tripping can occur.
Below a current factor of 3I0p Startpoint, which is set as a multiple of the basic
setting 3I0p PICKUP, no tripping can take place.
Further information regarding the effect of the various parameters can be found in the
setting information of the function parameters in Section 2.8.2.
The remaining setting options are the same as for the other curves.
Figure 2-90 Logic diagram of the 3I
0P
stage for the inverse logarithmic characteristic
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