GroundDisconnector not supported during CGMES import

[miovd]

• Do you want to request a feature or report a bug?
  Feature

• What is the current behavior?
  GroundDisconnector are ignored during CGMES import.

• What is the expected behavior?
  GroundDisconnector objects should be imported as switches during CGMES conversion.

• What is the motivation / use case for changing the behavior?
  It is in CGMES documentation and could be used.

• Please tell us about your environment:

  • PowSyBl Version: 3.2.0-SNAPSHOT

• Other information
  It might be necessary to add another SwitchKind (either GROUND_DISCONNECTOR or OTHER) for switches that do not have defined type.

[So-Fras]

Point of attention:
At first glance, nothing prevents someone from creating a switch with the "GROUND_DISCONNECTOR" type between 2 busbar sections. However, it does not make any sense.
Thus, using a new type of disconnector could be seen as a weak way to model ground disconnectors.

[So-Fras]

Another way to model ground disconnectors is to add a new equipment "Ground" and a ground disconnector will just be a disconnector that connects a Ground to the topology.

Question: what kind of equipment would the "Ground" be? It does not look like an Identifiable or an Extendable. Would it be a Singleton? What would be its electrical properties?

NB: in the CGMES import and export, one would have to be careful when converting ground disconnectors. One object in CGMES becomes two objects in IIDM (disconnector + ground)

[So-Fras]

There is another question about the loadflow calculation: what happen if we decide to close the ground disconnector?
Do we take it into account? If yes, how?

NB: in the current configuration, I think that opening or closing the ground disconnector will have no effect on the loadflow since one side of the ground disconnector is connected to "nothing".