Siemens SIPROTEC 7SA522 Manual page 155

Inverse Time Over-
current Stage with
Logarithmic–
Inverse
Characteristic
Figure 2-65 Logic diagram of the 3I
7SA522 Manual
C53000-G1176-C155-3
2.7 Earth fault overcurrent protection in earthed systems (optional)
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.
–stage for the inverse logarithmic characteristic
0P
155