5.1.7.4
Backup overcurrent function (O/C Backup)
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The distance protection function includes a definite time overcurrent unit as backup
protection. A starting signal Start O/C is set to logical
1, when one or more of the currents I
L1
,
I
L2
, and I
L3
exceed the setting of
I O/C. After the time O/C Delay, the tripping signal Trip O/C
to the system logic is set to logical
1.
Blocking signals generated by the distance, underimpedance starting, power swing blocking
or VT supervision functions do not influence the backup overcurrent function.
The overcurrent function is independent of the distance protection starters and, not having to
perform phase selection, can have a more sensitive setting.
5.1.7.5
System logic
Structure of the system logic
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The system logic processes the binary input signals from external plant (optocoupler inputs)
and all the binary signals of the distance protection function.
18000018-IEC19000420-1-en.vsdx
IEC19000420 V1 EN-US
Figure 19: System logic in the distance protection function
The system logic outputs are binary signals for controlling a disturbance recorder, LED signals
and auxiliary tripping and signaling relays.
Enabling and disabling logic (SUPBL)
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The logic of the VT supervision function (VTSUP segment) has already been described in the
relevant Section. The external blocking signals for distance protection [EXTBL_DIST] (opto-
Section 5
1MRK 505 406-UEN B
Bay protection functions
68
Bay protection functions REB500
Technical manual
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