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Functions
2.4 Backup overcurrent
[lo-i-3gr-stufe-20101115, 2, en_US]
Figure 2-27
Inverse Time Overcurrent Element 51
The logic of the inverse overcurrent element basically operates in the same way as the other elements. The
time delay, however, is calculated based on the type of the set characteristic, the intensity of the current and a
time multiplier (following figure). A pre-selection of the available characteristics was already carried out
during the configuration of the protection functions. Furthermore, an additional constant time delay 51-B
AddT-DELAY or 51N-B AddTdelay may be selected which is added to the inverse time. The possible charac-
teristics are shown in the Technical Data.
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
described in detail.
If parameter 51-B Inrush (address 2637) is set to YES, the element is blocked.
74
Logic diagram of the 50-3 element
2.4.4 Setting
Notes), the different setting addresses are
E50417-G1100-C474-A2, Edition 02.2018
SIPROTEC 4, 7SD80, Manual
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