EDR-3000 IM02602003E
Zone Coordination
General Description
What does Zone Coordination mean?
Zone Coordination means that the upstream protection device is doing a virtual autoreclosure while the downstream
protective device is doing a “real” autoreclosure. By means of the zone coordination, selectivity can be kept even if a
downstream protective device changes its tripping characteristic after a reclosure cycle. The virtual autoreclosure of
the upstream device follows the downstream autoreclosure.
What application can be realized by means of Zone Coordination?
A radial distribution system is protected by an upstream protective device (with a breaker) and a downstream protective
device with a reclosure and fuse. By means of the zone coordination, a “fuse saving scheme” might be realized. In
order to “save fuses”, the downstream protective device might trip for the first reclosure attempt at low tripping values
(undergrade the fuse, trying to avoid a damaging of the fuse). If the reclosure attempt fails, the tripping values might be
raised (overgrade the fuse) for the second reclosure attempt (using higher tripping values/characteristics).
What is essential?
The triggering thresholds of the upstream and the downstream devices have to be the same but the tripping times have
to be selectively.
How is Zone Coordination activated?
The zone coordination function is part of the autoreclosure element and it can be enabled by setting the parameter
»
Zone coordination«
as »
active«
within the [Protection Para/AR/General Settings] menu for an upstream feeder
protection device.
How does the Zone Coordination work (within the upstream protection device)?
When the zone coordination function is enabled, it works similar to a normal autoreclose function with the same setting
parameters: maximum reclosure attempts, dead timer for each shot, initiate functions for each shot, and other timers for
autoreclose process, but with the following zone coordination features to coordinate with the downstream reclosers.
The corresponding dead timer for each shot will be started even if the breaker of the upstream feeder relay is NOT
tripped from the assigned initiate protective functions.
The dead timer begins timing once the autoreclose senses a drawback of the assigned overcurrent protection
pickup signal. This exhibits that the fault current was tripped by the downstream recloser opening.
The shot counter of an enabled zone coordination will be incremented after the dead timer elapses, even there is no
breaker reclosing command issued. Meanwhile, the »T-RUN2READY« timer is started.
If a permanent fault exists after the downstream recloser is reclosed, the fault current makes the upstream
overcurrent protection pick up again, but with the pickup thresholds or operating curves controlled by the
www.eaton.com 519
To Next Page
Loading...
