A line charging current compensation provides increased
sensitivity of line differential protection.
Line differential protection 3 or 6 CT sets, with in-zone
transformers LT3CPDIF , LT6CPDIF
Two two-winding power transformers or one three-winding
power transformer can be included in the line differential
protection zone. In such application, the differential protection
is based on the ampere turns balance between the transformer
windings. Both two- and three-winding transformers are
correctly represented with vector group compensations made
in the algorithm. The function includes 2
nd
and 5
th
harmonic
restraint and zero-sequence current elimination. The phase-
segregated differential protection with single-pole tripping is
usually not possible in such applications.
IED
IED IED
Protected zone
Comm. Channel
Comm. Channel
Comm. Channel
IEC05000042_2_en.vsd
IEC05000042 V2 EN
Figure 8. Example of application on a three-terminal line with an in-line power transformer in the protection zone
Analog signal transfer for line differential protection
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
kbit/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
kbit/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
.
It is recommended to use the same firmware
version as well as hardware version for a
specific line differential scheme.
Protected zone
Comm.
Channels
IED
IED IED IED
IED
IEC0500043_2_en.vsd
IEC05000043 V2 EN
Figure 9. Five terminal lines with master-master system
1MRK 505 346-BEN -
Line differential protection RED670 2.1 IEC
Product version: 2.1
ABB 23
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