For DAB delta connected main CT ratio shall be set for √3 times smaller in RET 670 then theactual ratio of individual phase CTs. The “StarPoint” parameter, for this particular connectionshall be setToObject. It shall be noted that delta DAB connected main CTs must be connectedexactly as shown in figure 28.For more detailed info regarding CT data settings please refer to the three applicationexamples presented in section "Application Examples".6.1.3.3 Application Examples SEMOD167854-5 v2Three application examples will be given here. For each example two differential protectionsolutions will be presented:• First solution will be with all main CTs star connected.• Second solution will be with delta connected main CT on Y (that is, star) connected sidesof the protected power transformer.For each differential protection solution the following settings will be given:1. Input CT channels on the transformer input modules.2. General settings for the transformer differential protection where specific data aboutprotected power transformer shall be entered.Finally the setting for the differential protection characteristic will be given for all presentedapplications.Example 1: Star-delta connected power transformer without on-load tap-changerSEMOD167854-110 v6Single line diagrams for two possible solutions for such type of power transformer with allrelevant application data are given in figure 29.Section 6 1MRK 504 158-UEN ADifferential protection72Application manual
