Regardless which one of the above two options is selected, busbar differentialprotection will behave correctly.The main CT ratios must also be set. This is done by setting the two parameters CTsecand CTprim for each current channel. For a 1000/5 A CT, the following settings shallbe used:• CTprim = 1000 (value in A)• CTsec =5 (value in A).4.2.2.4 Examples on how to connect, configure and set CT inputs for mostcommonly used CT connections SEMOD55055-296 v7Figure 20 defines the marking of current transformer terminals commonly used aroundthe world:In the SMAI function block, you have to set if the SMAI block ismeasuring current or voltage. This is done with the parameter:AnalogInputType: Current/Voltage. The ConnectionType: phase -phase/phase-ground and GlobalBaseSel.ISecIPriS1 (X1)P1(H1)P2(H2)S2 (X2)P2(H2)P1(H1)x xa) b) c)en06000641.vsdS2 (X2) S1 (X1)IEC06000641 V1 EN-USFigure 20: Commonly used markings of CT terminalsWhere:a) is symbol and terminal marking used in this document. Terminals marked with a squareindicates the primary and secondary winding terminals with the same (that is, positive)polarityb) andc)are equivalent symbols and terminal marking used by IEC (ANSI) standard for CTs. Note thatfor these two cases the CT polarity marking is correct!1MRK 505 370-UUS A Section 4Analog inputsBusbar protection REB670 2.2 ANSI 73Application manual
