Star shunts

[flo-dup]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
Star-connected shunts are not handled

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem
Create a voltage level with at least 3 feeders and connect them all to a single node (see patterns below for better understanding)

What is the expected behavior?
Several way to handle this:

• (1) consider that two of the feeders are connected by a shunt and then add the connections to the other feeders on top of that shunt
• (2) consider that the center of this star can be displayed as a fictitious busbar (hence displayed by default with a thinner line)

I think the first one will change the definition of shunts and might therefore have a significant impact on layout calculations.

The second one is misleading as the node is not a bus, besides it changes the graph structure. But it demands less effort: it's just a matter of detecting this node and replacing it by a BusNode (in fact I already coded it quickly in a draft branch).

What is the motivation / use case for changing the behavior?
Corresponding real cases encountered

Other information
The real case encountered is more complex in fact, the center node can also be connected directly or indirectly to busbars