6.3
Line differential protection
IP13934-1 v1
6.3.1
Identification
M14844-1 v4
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Line differential protection, 3 CT
sets, 2-3 line ends
L3CPDIF
3Id/I>
SYMBOL-HH V1 EN-US
87L
Line differential protection, 6 CT
sets, 3-5 line ends
L6CPDIF
3Id/I>
SYMBOL-HH V1 EN-US
87L
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 protection 6 CT
sets, with in-zone transformers, 3-5
line ends
LT6CPDIF
3Id/I>
SYMBOL-HH V1 EN-US
87LT
Line differential logic
LDLPSCH
-
87L
6.3.2
Application
IP14947-1 v1
M12022-3 v5
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 five 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 505 343-UEN B
Section 6
Differential protection
115
Application manual
Summary of Contents for Relion 670 series
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