Regardless which one of the above two options is selected busbar differential protectionwill behave correctly.The main CT ratios must also be set. This is done by setting the two parameters CTsec andCTprim for each current channel. For a 1000/5 A CT the following setting shall be 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 connectionsFigure 20 defines the marking of current transformer terminals commonly used around theworld: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-earth 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 ENFigure 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) and c) are equivalent symbols and terminal marking used by IEC (ANSI) standard for CTs. Note that forthese two cases the CT polarity marking is correct!1MRK 505 337-UUS - Section 4Analog inputs67Application manual
