How to model zero-phase sequence current transformer? This type of current transformer isn't electrical connected to a cable or to bus,
therefore it can't contain Terminal elements.
You can model any kind of equipment without terminals, even non electrical ones, in the Substation hierarchy, and by using the Function / SubFunction elements. The main purpose from IEC 61850 point of view is to provide a plant related (functional) name to the data objects of the attached logical nodes.