The outputs of the open CT conditions are OPENCT and OPENCTAL.• OPENCT: Open CT detected• OPENCTAL: Alarm issued after the setting delayOutputs (positive integer) for information on the local HMI:• OPENCTIN: Open CT in CT group inputs (1 for input 1 and 2 for input 2)• OPENCTPH: Open CT with phase information (1 for phase L1, 2 for phase L2, 3 for phase L3)6.2.3 Setting guidelines SEMOD54832-1 v2M12541-86 v4Line differential protection receives information about currents from all line terminals andevaluates this information in three different analysis blocks. The results of these analyses arethen forwarded to an output logic, where the conditions for trip or no trip are checked.The three current analyses are:• Percentage restrained differential analysis• The 2nd and 5th harmonic analysis (only if there is a power transformer included in theprotected circuit)• Internal/external fault discriminator6.2.3.1 General settings M12541-93 v2IBase set in primary Amp M12541-95 v3Set a commonIBase in Global base for the protected line (circuit). Most current settings forthe protection function are then related to theIBase. The setting ofIBase is normally made sothat it corresponds to the maximum rated CT in any of the line terminals. For example, if allCTs used in a protected circuit are 1000A/1A, that is, the primary current rating is 1000 A, thenIBase = 1000 A is a good choice.NoOfUsedCTs M12541-98 v7NoOfUsedCTs indicates to the function the number of three-phase CT sets included in theprotected circuit. Note that one IED can process one or two local current terminals of theprotected circuit. This is the case, for example, in 1½ breaker configurations in the line bay,where one of the two CT sets will be represented as one separate current terminal. A two-terminal line with 1½ breaker configurations at one line end must consequently haveNoOfUsedCTs =3.Current terminalsIEC15000450-1-en.vsdRED670RED670IEC15000450 V1 EN-USFigure 40: Example when setting NoOfUsedCTs = 3 in 1½ breaker configurations(example showing 670 device)1MRK 505 363-UEN A Section 6Differential protection81Application manual
