Cgmes Export: Multiple islands after exporting an imported UCTE case to CGMES and reloading it

[marqueslanauja]

Describe the current behavior

• A UCTE case is first imported into the system and successfully loaded.
• The network is then exported to CGMES format without errors.
• When the exported CGMES files are loaded again, the network appears split into multiple electrical islands

Describe the expected behavior

After the three steps, the network was expected to remain a single connected component.

Describe the steps

Environment

No response

Relevant Log Output

No response

Extra Information

Issue reported in Slack.
The issue can be reproduced using the following case:
https://github.com/powsybl/pypowsybl/blob/main/data/19700101_0000_FO4_UX1.uct

[marqueslanauja]

A first analysis of the issue:

• After importing the UCTE case, the network has some TieLines represented by two paired danglinglines.
• When the network is exported to CGMES, each dangling line of the TieLine is exported as a ACLinesegment with different topologicalNode at the boundary terminal.
• As the two AcLinesegments created for each TieLine are not connected the network is split into multiple islands.

By default, the CGMES export process produces the CIM 16 version (CGMES 2.4).
When configuring the export process to produce the CIM 100 version (CGMES 3.0), the same ConnectivityNode is assigned to the boundary terminal of both ACLineSegments. The TopologicalNode is still incorrect (it differs), but since the system uses only the ConnectivityNode during the import process in this case, the network will end up as a single connected component.

To configure the CIM 100 version, the following property must be used:

Properties params = new Properties();
params.put("iidm.export.cgmes.cim-version", "100");