2.12 Line differential protection
LdI> (87L)
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Figure 2.12-3 Example BIAS and differential calculation
Data communication for differential current measurement is
effected via fibre-optic cables. 1550 nm single-mode fibre
provides communication up „till 120 km with external
communication modules.
Relay has special setting called “Line distance”. This setting
compensates the time delay between the relay caused by the
optic fiber. In case that the length of the fibre is 90 km the
setting has to be 90km as well.
Figure 2.12-4 CT wiring towards the line
The starting times of the phase currents calculation tasks in
two relays are synchronized. Function will block tripping until
the synchronization is achived. The default communication
speed is 64000 bps.
Serial remote port of the relay (RS-232) is used by line
differential protection. The recommended solution for the
communication channel is the supervised fibre optic wiring.
With multimode fibre cables and VSE001-GG fibre optic
modems the communication distance can be up to 1 km. When
using single mode fibre cables and third party converters the
distance can be up to tens of kilometres.
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