3) are three connections made in the Signal Matrix tool (SMT), Application configuration tool(ACT), which connects these three voltage inputs to first three input channels of thepreprocessing function block 5). Depending on the type of functions, which need thisvoltage information, more than one preprocessing block might be connected in parallel tothese three VT inputs4) shows that in this example the fourth (that is, residual) input channel of the preprocessingblock is not connected in SMT. Note. If the parameters UL1, UL2, UL3, UN should be usedthe open delta must be connected here.5) Preprocessing block has a task to digitally filter the connected analog inputs and calculate:• 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 forsequence quantities)These calculated values are then available for all built-in protection and control functionswithin the IED, which are connected to this preprocessing function block in theconfiguration tool. For this application most of the preprocessing settings can be left to thedefault values. However the following settings shall be set as shown here:ConnectionType=Ph-PhUBase=13.8 kVIf frequency tracking and compensation is required (this feature is typically required onlyfor IEDs installed in the generating stations) then the setting parametersDFTReferenceshall be set accordingly.4.2.4.5 Example on how to connect an open delta VT to the IED for highimpedance earthed or unearthed networks SEMOD55055-163 v9Figure 20 gives an example about the wiring of an open delta VT to the IED forhigh impedance earthed or unearthed power systems. It shall be noted that this typeof VT connection presents 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 willbe 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. Threeseries connected VT secondary windings gives a secondary voltage equal to threetimes the individual VT secondary winding rating. Thus the secondary windings ofopen delta VTs quite often have a secondary rated voltage equal to one third of therated phase-to-phase VT secondary voltage (110/3V in this particular example).Figure 20 gives overview of required actions by the user in order to make thismeasurement available to the built-in protection and control functions within theIED as well.1MRK 505 393-UEN B Section 4Analog inputsLine differential protection RED650 2.2 IEC 61Application manual
