2.7 Earth fault overcurrent protection in earthed systems (optional)
155
7SA522 Manual
C53000-G1176-C155-3
Inverse Time Over-
current Stage with
Logarithmic–
Inverse
C h a ra c te r i s ti c
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 ,S0D[7'(/$< which directly affect the
curve, can be changed. The characteristics are shown in the Technical Data.
Figure 2-65 shows the logic diagram. In addition to the curve parameters, a minimum
time ,S0LQ7'(/$< can be determined; below this time no tripping can occur.
Below a current factor of ,S6WDUWSRLQW, which is set as a multiple of the basic
setting ,S3,&.83, 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 Sub-section 2.7.2.
The remaining setting options are the same as for the other curves.
Figure 2-65 Logic diagram of the 3I
0P
–stage for the inverse logarithmic characteristic
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