3) are three connections made in Signal Matrix Tool (SMT), which connect these threevoltage inputs to first three input channels of the preprocessing function block 5).Depending on the type of functions which need this voltage information, more then onepreprocessing block might be connected in parallel to these three VT inputs.4) shows that in this example the fourth (that is, residual) input channel of thepreprocessing block is not connected in SMT tool. Thus the preprocessing block willautomatically calculate 3Uo inside by vectorial sum from the three phase to earthvoltages connected to the first three input channels of the same preprocessing block.Alternatively, the fourth input channel can be connected to open delta VT input, asshown in Figure 23.5) is a Preprocessing block that has the task to digitally filter the connected analog inputsand calculate:• fundamental frequency phasors for all input channels• harmonic content for all input channels• positive, negative and zero sequence quantities by using the fundamentalfrequency phasors for the first three input channels (channel one taken asreference for sequence quantities)These calculated values are then available for all built-in protection and controlfunctions within the IED, which are connected to this preprocessing function block in theconfiguration tool. For this application most of the preprocessing settings can be left tothe default values. However the following settings shall be set as shown here:UBase=66 kV (that is, rated Ph-Ph voltage)If frequency tracking and compensation is required (this feature is typically requiredonly for IEDs installed in the generating stations) then the setting parametersDFTReference shall be set accordingly.4.2.4.4 Example on how to connect a phase-to-phase connected VT to theIED SEMOD55055-134 v7Figure 22 gives an example how to connect a phase-to-phase connected VT to theIED. It gives an overview of the required actions by the user in order to make thismeasurement available to the built-in protection and control functions within theIED. It shall be noted that this VT connection is only used on lower voltage levels(that is, rated primary voltage below 40 kV).1MRK 511 401-UEN A Section 4Analog inputsBay control REC670 2.2 IEC 81Application manual