4.2.4.6 Example how to connect the open delta VT to the IED for lowimpedance grounded or solidly grounded power systems SEMOD55055-199 v6Figure 32 gives an example about the connection of an open delta VT to the IED forlow impedance grounded or solidly grounded power systems. It shall be noted that thistype of VT connection presents secondary voltage proportional to 3V0 to the IED.In case of a solid ground fault close to the VT location the primary value of 3Vo will beequal to:3 3Ph PhPh GndVVo V--= =EQUATION1927-ANSI V1 EN-US (Equation 7)The primary rated voltage of such VT is always equal to VPh-Gnd. Therefore, threeseries connected VT secondary windings will give the secondary voltage equal only toone individual VT secondary winding rating. Thus the secondary windings of suchopen delta VTs quite often has a secondary rated voltage close to rated phase-to-phaseVT secondary voltage, that is, 115V or 115/√3V as in this particular example. Figure32 gives an overview of the actions which are needed to make this measurementavailable to the built-in protection and control functions within the IED.1MRK 505 370-UUS A Section 4Analog inputsBusbar protection REB670 2.2 ANSI 93Application manual
