3) are three connections made in Signal Matrix Tool (SMT), which connect these three voltageinputs to first three input channels of the preprocessing function block 5). Depending on thetype of functions which need this voltage information, more then one preprocessing block mightbe connected in parallel to these three VT inputs.4) shows that in this example the fourth (that is, residual) input channel of the preprocessing blockis not connected in SMT tool. Thus the preprocessing block will automatically calculate 3Uoinside by vectorial sum from the three phase to earth voltages connected to the first three inputchannels of the same preprocessing block. Alternatively, the fourth input channel can beconnected to open delta VT input, as shown in figure 18.5) is a Preprocessing block that has the task to digitally filter the connected analog inputs andcalculate:• fundamental frequency phasors for all four input channels• harmonic content for all four input channels• positive, negative and zero sequence quantities by using the fundamental frequencyphasors for the first three input channels (channel one taken as reference for sequencequantities)These calculated values are then available for all built-in protection and control functions withinthe IED, which are connected to this preprocessing function block in the configuration tool. Forthis application most of the preprocessing settings can be left to the default values. However thefollowing 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 required only for IEDsinstalled in the generating stations) then the setting parametersDFTReference shall be setaccordingly.4.2.4.4 Example on how to connect a phase-to-phase connected VT to the IEDSEMOD55055-134 v6Figure 17 gives an example how to connect a phase-to-phase connected VT to the IED. It givesan overview of the required actions by the user in order to make this measurement available tothe built-in protection and control functions within the IED as well. It shall be noted that thisVT connection is only used on lower voltage levels (that is, rated primary voltage below 40 kV).Section 4 1MRK 505 355-UEN AAnalog inputs48Application manual
