44x/EN AP/Hb6
-78 MiCOM P40 Agile
The major disadvantage of blocking schemes is highlighted in Figure 51 (iii) where fault
current is outfeed from a terminal for an internal fault condition. relay 'C' sees a reverse fault
condition. This results in a blocking signal being sent to the two remote line ends, preventing
tripping until the normal zone 2 time delay has expired.
3.5 Distance protection logic
The following diagram gives the logic of the distance protection:
Figure 52: Mimic diagram
3.5.1 Blocking / unblocking logic
The zones unblocking/blocking logic with power swing are managed as explained in the
section 3.2.
3.5.1.1 Distance protection by zones and unblocking / blocking logic with power swing
The logic of the distance protection by zones (including power swing basic unblocking /
blocking logic) is shown in the following diagram:
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