4.2.4.5 Example on how to connect an open delta VT to the IED for highimpedance earthed or unearthed netwoeks SEMOD55055-163 v8Figure 18 gives an example about the wiring of an open delta VT to the IED for high impedanceearthed or unearthed power systems. It shall be noted that this type of VT connectionpresents a secondary voltage proportional to 3U0 to the IED.In case of a solid earth fault close to the VT location the primary value of 3Uo will be equal to:3 0 3 3Ph Ph Ph NU U U- -= × = ×EQUATION1921 V3 EN-US (Equation 3)The primary rated voltage of an open Delta VT is always equal to UPh-E. Three series connectedVT secondary windings gives a secondary voltage equal to three times the individual VTsecondary winding rating. Thus the secondary windings of open delta VTs quite often have asecondary rated voltage equal to one third of the rated phase-to-phase VT secondary voltage(110/3V in this particular example).Figure 18 gives overview of required actions by the user in order to make this measurementavailable to the built-in protection and control functions within the IED as well.L1IEDL2L36.63 1103kVV+3Uo6.63 1103kVV6.63 1103kVV1243# Not Used5IEC06000601-4-en.vsdx# Not Used# Not UsedSMAI2BLOCKREVROT^GRP2L1^GRP2L2^GRP2L3^GRP2NAI3PAI1AI2AI3AI4AINIEC06000601 V4 EN-USFigure 18: Open delta connected VT in high impedance earthed power systemSection 4 1MRK 504 158-UEN AAnalog inputs48Application manual
