A network with mixed topology kind (node-breaker and bus-breaker) should be exported to CGMES as bus-branch.

[rcourtier]

Describe the current behavior

In PowSyBl, a topology kind is defined for each VoltageLevel, and it's perfectly fine to have overall in the network a mixed topology kind, that is have some VoltageLevel in NODE_BREAKER and some other VoltageLevel in BUS_BREAKER topology kind.

With the current CGMES exporter, when at least one VoltageLevel is in NODE_BREAKER, the whole network is considered a NODE_BREAKER and the connectivity is exported as follow:

• NODE_BREAKER VoltageLevel's nodes of the NodeBreakerView will be exported as CGMES ConnectivityNode
• BUS_BREAKER VoltageLevel's buses of the BusBreakerView will be exported as CGMES ConnectivityNode

Quality/UML-wise, the export is correct. However, this is misleading since what is exported is not the detailed connectivity (for bus-breaker voltage levels) but the topology disguised as connectivity.

Describe the expected behavior

The CGMES export of a network with a mixed topology kind should be a bus-branch export: when at least one VoltageLevel is in BUS_BREAKER topology kind, no ConnectivityNode should be exported, only the TopologycalNode from the Buses of the BusBreakerView.

Describe the motivation

The main reason is to not mislead in any way about the exported file and not pretend the network is entirely a node-breaker when it is at least partly a bus-branch.

Extra Information

This is handled in #3315.
The default topology kind for hybrid network depends on the CIM version for export:

• For CIM 16 exports, hybrid networks are exported as BUS_BRANCH. Detailed connectivity of VoltageLevel in NODE_BREAKER will be lost. To remedy it, a NODE_BREAKER export can be requested.
• For CIM 100 exports, hybrid networks are exported as NODE_BREAKER. In that case, ConnectivityNode are written even for VoltageLevel in BUS_BREAKER topology kind (for such VoltageLevel, ConnectivityNode are exported from Buses of the BusBreakerView).

[zamarrenolm]

Be aware that with this approach we will lose information in the export. The parts of the network that were specified as node/breaker will be simplified in the output.

Also, for CGMES 3, even exporting a bus/breaker model requires writing CGMES connectivity nodes. Exporting a bus/breaker model using base connectivity designed for node/breaker is valid, and seems the approach chosen by CGMES.

[rcourtier]

Be aware that with this approach we will lose information in the export. The parts of the network that were specified as node/breaker will be simplified in the output.

Also, for CGMES 3, even exporting a bus/breaker model requires writing CGMES connectivity nodes. Exporting a bus/breaker model using base connectivity designed for node/breaker is valid, and seems the approach chosen by CGMES.

This is handled in #3315. In case of a CIM 16 export, we will indeed by default lose the detailed connectivity in the export. But there is a simple way not to: explicitely request a node-breaker export by setting a parameter (added in 3315) so that the connectivity is exported.
As for CIM 100 export, the node-breaker export will be the default export type for hybrid networks so by default no information will be lost.