CGMES reference priority bad conversion

[annetill]

Describe the current behavior

This is the current conversion of referencePriority in CGMES:

        if (p.asInt("referencePriority", 0) > 0) {
            // We could find multiple generators with the same priority,
            // we will only change the terminal of the slack extension if the previous was not connected
            SlackTerminal st = g.getTerminal().getVoltageLevel().getExtension(SlackTerminal.class);
            if (st == null) {
                SlackTerminal.reset(g.getTerminal().getVoltageLevel(), g.getTerminal());
            } else if (!st.getTerminal().isConnected()) {
                st.setTerminal(g.getTerminal());
            }
        }

But it is a bad interpretation. The slack terminal defines the bus to handle renaming active power slack in a power flow engine. But we also have in a power flow engine a bus to define the angle reference, and it could be different from the slack bus. The reference priority refers to the angle reference bus in CGMES.

Describe the expected behavior

We have to create a specific extension for the angle reference terminal, the same way we have a slack terminal extension. And fix the CGMES conversion.

Describe the steps

No response

Environment

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Relevant Log Output

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Extra Information

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