Siemens SIPROTEC 7SD610 Manual page 96

Functions
2.8 Instantaneous High-Current Switch-onto-Fault Protection (SOTF)
Figure 2-36 Activation of the I>>> stage
I>>>> stage
The I>>>> stage trips regardless of the position of the circuit breakers. Here, the currents are also numerically
filtered and the peak value of the currents is measured from the double setting value onwards. Figure 2-37
shows the logic diagram in the upper part.
Therefore, this stage is used when current grading is possible. This is possible with a small source impedance
and at the same time a high impedance of the protected object (an example can be found in the advice on
setting notes, Section 2.8.2).
The I>>>> stage is enabled automatically by the current-step monitoring
ms. This stage operates separately for each phase.
96
dI
/ of the device for a duration of 50
dt
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011