Siemens SIPROTEC 7SD80 Manual page 81

The non-directional and the directional inverse time overcurrent element 51 always uses the same character-
istic curve that is parameterized via 2642 (IEC) or 2643 (ANSI). Different inverse times and additional times
can be parameterized here.
The following figure shows the logic diagram. The setting addresses of the IEC characteristic curves are shown
by way of example. In the setting notes (Section 2.4.4), the different setting addresses are described in detail.
If parameter 51-B Inrush (address 2637) is set to YES, the element is blocked.
Figure 2-28 Logic diagram of the 51 element (inverse time overcurrent protection) - example for IEC characteristic
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
Functions
2.4 Backup Overcurrent
81