I_AI_BI_Cen05000343_ansi.vsdTime [cycles]400kV CurrentsCurrent [%]ANSI05000343 V1 ENFigure 36: Inrush currents to a transformer as seen by a protection IED. Typical isa high amount of the 2nd harmonic, and intervals of low current, andlow rate-of-change of current within each period.Cross-blocking between phasesWith the cross-blocking function, one of the three phases can block operation of theother two phases due to the harmonic pollution of the differential current in that phase(that is, waveform, 2nd or 5th harmonic content). In differential algorithm the user cancontrol the cross-blocking between the phases via the setting parameter CrossBlockEn.When parameter CrossBlockEn=Enabled cross blocking between phases is introduced.There is no time settings involved, but the phase with the operating point above the setbias characteristic (in the operate region) will be able to cross-block other two phases ifit is itself blocked by any of the previously explained restrained criteria. If the startsignal in this phase is removed, that is, reset from TRUE to FALSE, cross blockingfrom that phase will be inhibited. In this way cross-blocking of the temporary nature isachieved. It should be noted that this is the default (recommended) setting value forthis parameter.When parameter CrossBlockEn=Disabled, any cross blocking between phases will bedisabled. It is recommended to use the value Disabled with caution in order to avoidthe unwanted tripping during initial energizing of the power transformer.6.1.3.12 Switch onto fault featureTransformer differential function in the IED has a built-in, advanced switch onto faultfeature. This feature can be enabled or disabled by a setting parameter SOTFMode.When enabled this feature ensures quick differential protection tripping in cases whereSection 6 1MRK 502 043-UUS BDifferential protection102Technical Manual
