Analog signal transfer for line differential protection
M13647-3 v8
The line differential protection function can be arranged
as a master-master system or a master-slave system
alternatively. In the former, current samples are
exchanged between all IEDs, and an evaluation is made
in each IED. This means that a 64 kbits/s or 2 Mbit/s
communication channel is needed between every IED
included in the same line differential protection zone. In
the latter, current samples are sent from all slave IEDs to
one master IED where the evaluation is made, and trip
signals are sent to the remote ends when needed. In this
system, a 64 kbits/s or 2 Mbit/s communication channel
is only needed between the master and each one of the
slave IEDs. The Master-Slave condition for the
differential function appears automatically when the
setting
Operation
for the differential function is set to
Off
.
For line differential protection we
recommend that all feeder ends use the
same version of RED670 and the line
data communication module LDCM.
The line differential protection in the
latest version of RED670 is compatible
with older versions of RED670. Older
versions than 670 1.2.3 must be verified
with ABB.
Protected zone
Comm.
Channels
IED
IED IED IED
IED
IEC0500043_2_en.vsd
IEC05000043 V2 EN-US
Figure 9. Five terminal lines with master-master system
IED
Protected zone
Comm. Channels
IED IED IED
IEC050000 44-2-
en.vsd
IED
IED
IEC05000044 V2 EN-US
Figure 10. Five terminal line with master-slave system
Current samples from IEDs located geographically apart
from each other, must be time coordinated so that the
current differential algorithm can be executed correctly,
this is done with the echo method. For applications
where transmit and receive times can differ, the
optional built-in GPS receivers can be used.
The communication link is continuously monitored, and
an automatic switchover to a standby link is possible
after a preset time.
Additional security logic for differential protection
LDRGFC
GUID-8F918A08-E50E-4E7B-BDCA-FF0B5534B289 v3
Additional security logic for differential protection
(LDRGFC) can help the security of the protection
especially when the communication system is in
abnormal status or for example when there is
unspecified asymmetry in the communication link. It
helps to reduce the probability for mal-operation of the
protection. LDRGFC is more sensitive than the main
Line differential protection RED670
1MRK 505 379-BEN N
Hitachi Power Grids 31
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