5-108 G30 Generator Protection System GE Multilin5.4 SYSTEM SETUP 5 SETTINGS5Figure 5–26: EXAMPLE TRANSFORMERThe above diagram shows the physical connections within the transformer that produce a phase angle in the delta windingthat lag the respective wye winding by 30°. The currents in the windings are also identified. Note that the total current out ofthe delta winding is described by an equation. Now assume that a source, with a sequence of ABC, is connected to trans-former terminals ABC respectively. The currents that would be present for a balanced load are shown the diagram below.Figure 5–27: PHASORS FOR ABC SEQUENCENote that the delta winding currents lag the wye winding currents by 30° (in agreement with the transformer nameplate).Now assume that a source, with a sequence of ACB is connected to transformer terminals A, C, and B, respectively. Thecurrents present for a balanced load are shown in the Phasors for ACB Phase Sequence diagram.Figure 5–28: PHASORS FOR ACB SEQUENCENote that the delta winding currents leads the wye winding currents by 30°, (which is a type Yd11 in IEC nomenclature anda type Y/d330 in GE Multilin nomenclature) which is in disagreement with the transformer nameplate. This is because thephysical connections and hence the equations used to calculate current for the delta winding have not changed. The trans-former nameplate phase relationship information is only correct for a stated phase sequence.828716A1.CDRAII I II I II I II I I- - -= = =I IAa b ca l b l cla l bl c lc l al b lB CB C Na b cIIIIIIIII –––IIAabcIc lblalclalb lBC828718A1.CDRIIIIIIIIII–––IIAabcclb lalcla lblB C
