Functions
2.8 Earth Fault Protection in Earthed Systems (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
221
Figure 2-105 Logic diagram of the 3I
0P
stage (inverse time overcurrent protection), example for IEC characteristics
Inverse time overcurrent stage with logarithmic inverse characteristic
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 parameters. 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 2-106 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.
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