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Scheme communication logic for residual
overcurrent protection (EFC)
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This communication logic is intended for residual overcurrent protections.
To achieve fast fault clearing for a fault on the part of the line not covered by the instan-
taneous zone 1, the directional residual overcurrent protection function can be support-
ed with logic, that uses communication channels.
One communication channel in each direction, which can transmit an on/off signal is
required. The performance and security of this function is directly related to the trans-
mission channel speed and security against false or lost signals. So special channels are
used for this purpose. When power line carrier is used for communication, these special
channels are strongly recommended due to the communication disturbance caused by
the primary fault.
In the directional comparison scheme, information of the fault current direction must be
transmitted to the other line end.
With directional comparison, an operate time of 50-60 ms, including a channel trans-
mission time of 20 ms, can be achieved. This short operate time enables rapid automatic
reclosing function after the fault.
During a single-phase reclosing cycle, the auto-reclosing device must block the direc-
tional comparison earth-fault scheme.
The communication logic module for the REx 5xx terminal contains circuits for block-
ing overreach and permissive overreach schemes.
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The directional comparison function contains logic for blocking overreach and permis-
sive overreach schemes.
Use the independent or inverse time functions in the directional earth-fault protection
module to get back-up tripping in case the communication equipment malfunctions that
prevents operation of the directional comparison logic.
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