Creating a Three-Leg Transformer Core
You can create a three-leg transformer core manually by setting the value of InfoCore to 0.
Examples of a three-leg transformer core are shown in TransCore when Stages is not 1 and WidthYoke is 0, TransCore when Stages is not 1 and WidthYoke is not 0, TransCore when Stages is 1 and WidthYoke is not 0, and Parameters of TransCore in axial direction (when Stages is 1 and WidthYoke is not 0).
You can assign the value of this property either when creating a three-leg transformer or after creating it, as described in Creating a Band and Creating an Outer Region, respectively.