2.12 Line differential protection
LdI> (87L)
2 Protection functions
Technical description
80
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VM59.EN001
Figure 2.12-5 Enabling line differential communication
Line differential protection has no operation delay. When the
difference between phase currents has been greater than the
threshold for two task cycles, the device will trip. Typical
tripping time in fault situation is 35 ms.
In case of the communcation channel failure the line
differential protection is inactive.
Line differential trip signal as well as communication channel
failure status are available as inputs in the output matrix and
blocking matrix of the relay.
Figure 2.12-6 Communication failure
The communication channel between two line differential
protection relays carries also binary signals in both directions:
the status of LDP 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.
Up to 16 binary signals can be sent between the relays. Signals
are updated every 10 ms. POC-signals are tied to line
differential algorithm which is operating after every half cycle
(50Hz).
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