The most typical
application
YNdx
d
CB
CT
CT
CB
Y
IED
CB
CB
CB
CB
Autotransformer
The most complicated
application - autotransformer
CT
CT
CT CT
IEC05000058-2 V1 EN
Figure 5. Examples of applications of the REFPDIF
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
The three-terminal version 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.
IEC05000039-3-en.vsd
Protected zone
Communication channel
IED IED
IEC05000039 V3 EN
Figure 6. Example of application on a conventional two-terminal line
The six-terminal versions are 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.
Protected zone
Comm. Channel
IEC05000040_2_en.vsd
IED
IED
IED
Comm. Channel
Comm. Channel
IEC05000040 V2 EN
Figure 7. Example of application on a three-terminal line with 1½ breaker arrangements
The current differential algorithm provides high sensitivity for
internal faults and it has excellent stability for external faults.
Current samples from all CTs are exchanged between the IEDs
in the line ends (master-master mode) or sent to one IED
(master-slave mode) for evaluation.
A restrained dual biased slope evaluation is made where the
bias current is the highest phase current in any line end, giving a
secure through-fault stability even with heavily saturated CTs.
In addition to the restrained evaluation, an unrestrained
(instantaneous) high differential current setting can be used for
fast tripping of internal faults with very high currents.
A special feature with this function is that applications with
small power transformers (rated current less than 50% of the
differential current setting
IdMin
) connected as line taps (that is,
as shunt power transformers), without measurements of
currents in the tap, can be handled. The normal load current is
considered to be negligible, and special measures must be
taken in the event of a short circuit on the LV side of the
transformer. In this application, the tripping of the differential
protection can be time-delayed for low differential currents to
achieve coordination with downstream overcurrent IEDs. The
local protection of the small tap power transformer is given the
time needed to disconnect the faulty transformer.
1MRK 505 346-BEN -
Line differential protection RED670 2.1 IEC
Product version: 2.1
22 ABB
To Next Page
Loading...
