ANSI11000304 V1 EN-US
Figure 243: Load encroachment characteristics
7.15.7.5 Under voltage seal-in
GUID-03357A87-A879-477C-ADBE-CC28AB54D34E v4
The under voltage seal-in logic ensures the trip under fault condition, where as under impedance
function will reset due to CT saturation. The pickup signal of zone 2 and zone 3 elements trigger
the under voltage seal-in. This can be selected using the setting
OpMode27pickup
. The setting
OpMode27pickup
can be selected as
Disabled
or
Z2pick up
or
Z3pick up
. Select
Z2Start
to choose
zone 2 for triggering the seal-in logic. Similarly, select
Z2pick up
to choose zone 3 for triggering
the seal-in logic.
Under voltage seal-in is activated from the criterion based on line-to-line voltage magnitude. The
voltage criteria checks by comparing all three line-to-line voltage levels with the level given by the
setting parameter
27_COMP
. If any loop detects lower voltage, the under voltage seal-in logic gets
triggered, provided the respective selected zone start is also high. Once the under voltage seal-in
logic is triggered, the pick-up signal 27 PU becomes high. If it is constantly high for a time longer
than the setting
timeDelay27
, the tripping signal 27 Trip is issued as a pulse signal with a duration
of one second.
Figure
244 shows the functionality of under voltage seal-in for zone 2 and zone 3.
1MRK 502 066-UUS B Section 7
Impedance protection
445
Technical manual
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