ABB RED650, Applications Manual

Page: 83 / 454

Section 6 Differential protection
6.1 Line differential protection
IP13934-1 v1
6.1.1 Identification
M14844-1 v4
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Line differential protection 3 CT sets,
with in-zone transformers, 2-3 line ends
LT3CPDIF
3Id/I>
SYMBOL-HH V1 EN-US
87LT
Line differential logic LDLPSCH - 87L
6.1.2 Application
IP14947-1 v1
M12022-3 v6
Line differential protection can be applied on overhead lines and cables. It is an
absolute selective unit protection with a number of advantages. Coordination with
other protections is normally simple. All faults on the line, between the line bay
CTs, can be cleared instantaneously. The sensitivity can be made high, which is
especially important for the ability to detect high resistive earth faults. It is not
influenced by possible voltage and/or current inversion, associated with faults in
series compensated networks. It is not influenced by fault current reversal at earth
faults on parallel lines. As it is phase-segregated, the identification of faulted
phases is inherent, and thus the application of single- or two-phase trip and auto-
reclosing can be made robust and reliable. Note that if an in-line or shunt power
transformer is included in the protected circuit, of the type Dy or Yd, then the
protection cannot be phase-segregated. Single-phase automatic re-closing will not
be possible.
Line differential protection can be applied on multi-terminal lines with maximum
three line ends. Depending on the actual network, reliable fault clearance can often
be difficult to achieve with conventional distance protection schemes in these types
of applications.
It is recommended to use the same firmware version as well as
hardware version for a specific line differential scheme.
1MRK 505 393-UEN B
Section 6
Differential protection
Line differential protection RED650 2.2 IEC 77
Application manual