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2.5 Line differential protection LdI>
(87)
2 Protection functions
Technical description
72
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VM259.EN007
Definite operation time of the LdI> stage can be configured,
starting with 60 ms as the minimum value.
When the difference between resistive currents current has
been greater than the threshold for at least 60 ms the line
differential stage starts to count the operation time according
to the configured parameter. If the difference between resistive
currents drops below the threshold while counting, the
counting to trip is stopped. If the difference between resistive
currents remains like this for at least the time defined as the
release delay (default 5 ms), the counting is cleared and the
relay start is also cleared.
In case of the pilot channel failure the line differential
protection is inactive.
LDP Start and Trip signals as well as pilot channel failure
status are available as inputs in the output matrix and
blocking matrix of the relay.
The pilot channel between two line differential protection
relays carries also binary signals in both directions: the status
of LDP Start and Trip signals, and the Remote Trip command
signal which is an output from the output logic matrix of the
sending relay. Remote Trip signal can be processed as an input
in the output matrix and blocking matrix of the receiving relay.
Parameters of the line differential protection stage LdI> (87):
Parameter
Value/unit
Description
Setting
values
dI> pick-up
I
n
Basic setting for lower
phase currents
Start of slope
I
n
Phase current limit for
applying linear threshold
characteristics
Slope
%
Linear characteristics slope
Operation
delay
[0.050 ..
3.000] / s
Operation time
Default 0.050
CT primary
other
[10 .. 20000] CT ratio of the other unit
Default 500
Recorded
values
SCntr
Start counter (Start)
reading
TCntr
Trip counter (Trip) reading
dI> status
Protection state