I worked on fixing the pandapower importer in the past. I certainly still need updates and better test coverage in PyPSA. If switches and three-winding transformers are important, I would recommend you to add those components to PyPSA incl. tests. This would probably make a pandapower importer easier to design and generally useful - we could then easily access pandapowers IEEE test networks and CIM importer.
Check out those threads:
- Issues · PyPSA/PyPSA · GitHub
- Restore pandapower importer and add tests by pz-max · Pull Request #332 · PyPSA/PyPSA · GitHub
- Seems someone also worked on the three-winding transformer implementation… and Tom Brown made also some suggestions here: WIP: Switches by jankaeh · Pull Request #137 · PyPSA/PyPSA · GitHub
Having the BZR done with PyPSA would be cool!