Section 6 Differential protection6.1 Line differential protection IP13934-1 v16.1.1 IdentificationM14844-1 v4Function description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberLine differential protection 3 CT sets,with in-zone transformers, 2-3 line ends LT3CPDIF 3Id/I>SYMBOL-HH V1 EN-US87LTLine differential logic LDLPSCH - 87L6.1.2 Application IP14947-1 v1M12022-3 v6Line differential protection can be applied on overhead lines and cables. It is anabsolute selective unit protection with a number of advantages. Coordination withother protections is normally simple. All faults on the line, between the line bayCTs, can be cleared instantaneously. The sensitivity can be made high, which isespecially important for the ability to detect high resistive earth faults. It is notinfluenced by possible voltage and/or current inversion, associated with faults inseries compensated networks. It is not influenced by fault current reversal at earthfaults on parallel lines. As it is phase-segregated, the identification of faultedphases 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 powertransformer is included in the protected circuit, of the type Dy or Yd, then theprotection cannot be phase-segregated. Single-phase automatic re-closing will notbe possible.Line differential protection can be applied on multi-terminal lines with maximumthree line ends. Depending on the actual network, reliable fault clearance can oftenbe difficult to achieve with conventional distance protection schemes in these typesof applications.It is recommended to use the same firmware version as well ashardware version for a specific line differential scheme.1MRK 505 393-UEN B Section 6Differential protectionLine differential protection RED650 2.2 IEC 77Application manual
