Hitachi Relion 670 Series Product Manual page 33

Line differential protection RED670
Version 2.2
YNdx
CT
d
Y
CB CB
CT
IED
The most typical
application
IEC05000058-2 V1 EN-US
Figure 5. Examples of applications of the REFPDIF
High speed line differential protection for 4 CT sets,
2-3 line ends L4CPDIF
High speed line differential protection for 4 CT sets, 2-3 line
ends (L4CPDIF) is a unit type protection system with typical
operate time less than one cycle. These types of systems
are suitable for the protection of complex transmission
network configurations because they exhibit good
performance during evolving, inter-circuit, and cross-country
faults. They are also highly immune to power swings,
mutual coupling and series impedance unbalances. High
speed line differential protection requires 2 Mbit/s
communication channel to transfer analog signals.
The L4CPDIF function applies the Kirchhoff's law, and
compares currents entering and leaving the protected multi-
end circuit consisting of overhead power lines and cables.
Under normal load conditions, the sum of currents is small
or close to zero. The function is phase-segregated: each
phase has its own differential, bias and incremental
currents.
L4CPDIF measures currents at all ends of a protected
circuit. At each physical end, currents are mostly measured
IED
IEC05000039 V3 EN-US
Figure 6. Example of application on a conventional two-terminal line
L6CPDIF is used for conventional two-terminal lines with 1½
circuit breaker arrangements in both ends, as well as multi-
terminal lines with up to five terminals.
Hitachi Energy
CT CT
CB
CB
Autotransformer
CB CT
CB
CT
The most complicated
application - autotransformer
IEC05000058-2-en.vsd
GUID-57872A74-462D-4513-B75B-A46ADCE03522 v2
Protected zone
Communication channel
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by one and sometimes by two three-phase current
transformer (CT) groups. The voltages at all ends are also
measured if the exact method is selected for charging
current compensation. The protected zone is determined by
the positions of the CTs at all ends of the protected circuit.
L4CPDIF protects all electrical equipment, such as power
lines, circuit breakers and small tap transformers, that are
within the protected zone.
The information on all locally measured currents is
transmitted via communication channels to remote IEDs.
Then L4CPDIF compares these currents using a classical
current differential principle supplemented by an additional
advanced internal fault detector. This results in fast
protection with very high dependability (relay operates
correctly with faults it was designed for) and very high
security (relay does not operate with faults it was not
designed for).
Line differential protection, 3 or 6 CT sets L3CPDIF,
L6CPDIF
Line differential protection applies the Kirchhoff's law and
compares the currents entering and leaving the protected
multi-terminal circuit, consisting of overhead power lines
and cables. Under the condition that there are no in-line or
tap (shunt) power transformers within the zone of
protection, it offers a phase segregated fundamental
frequency current based differential protection with high
sensitivity and provides phase selection information for
single-pole tripping
L3CPDIF is used for conventional two-terminal lines with or
without a 1½ circuit breaker arrangement in one end, as
well as three-terminal lines with single breaker
arrangements at all terminals.
IED
IEC05000039-3-en.vsd
1MRK 505 379-BEN R
M14917-3 v7
33