0 deg180 deg90 deg270 deg120 degIMinNegSeqIf one or theother ofcurrents is toolow, then nomeasurementis done, and120 degreesis mappedExternalfaultregionInternalfaultregionInternal/externalfault boundaryNegSeqROA(RelayOperateAngle)en05000188-3-en.vsdIEC05000188 V3 EN-USFigure 40: Negative sequence current function Relay Operate Angle (ROA)IminNegSeq M12541-223 v4IminNegSeq is set as a multiple of IBase. The local, and the sum of all remotenegative sequence currents are compared separately if they are above the setthreshold value IminNegSeq. If either is below the threshold, no comparison ismade. Neither internal nor external fault is declared in this case. The default value0.04 × IBase can be used if no special considerations, such as extremely weeksources, are taken into account. Observe that internally, whenever the bias currentis higher than 1.5 times IBase, the actual threshold is equal to the sum ofIminNegSeq + 0.1 Ibias. This is in order to prevent wrong decisions of the internal/external fault discriminator under heavy three-phase external fault conditions withsevere CT saturation.6.1.3.5 Power transformers in the protected zone M12541-6 v7One three-winding transformer or two two-winding transformers can be included inthe line protection zone. The alternative with one two-winding transformer in theprotected zone is shown in Figure 41 and Figure 42.1MRK 505 393-UEN B Section 6Differential protectionLine differential protection RED650 2.2 IEC 93Application manual
