To define a Y-connection:
1. Click Maxwell 2D (or Maxwell 3D)>Excitations>Setup Y Connection.
The Setup Y Connection dialogue appears.
2. In the Winding list on the left, select the windings to be grouped into a Y connection.
3. Click the Group button to create a Y Connection group with the selected windings.
4. Click OK when all required grouping have been created.
You can refer to the "Setting Up a Y Connection in 2D and 3D Transient Designs" section in Maxwell help