Deliver i and v values on DC loadflows

[nicow-elia]

Describe the current behavior

When running DC loadflows, powsybl currently returns NaN for net.get_branches()["i1"] and net.get_buses()["v_mag"]

Describe the expected behavior

While it's correct that the DC loadflows don't return q values, v and i values are actually defined in the DC loadflow framework. v is defined to be just v_nominal and hence I can be computed through i = p / (sqrt(3) * v_nominal).

It would be nice if these values are returned, both for the normal loadflows and for the security analysis, as it makes comparing with current limits easier. Especially the i value is important there but logically the v_mag value could also be returned.

Describe the motivation

No response

Extra Information

A simple implementation in python could look like this

injections = pd.merge(
    left=net.get_injections(),
    right=net.get_voltage_levels()["nominal_v"],
    left_on="voltage_level_id",
    right_index=True,
)
injections["i"] = (
    injections["p"] / (injections["nominal_v"] * math.sqrt(3) * 1e-3)
).abs()
del injections["nominal_v"]

and

branches = pd.merge(
    left=net.get_branches(),
    right=net.get_voltage_levels()["nominal_v"].rename("nominal_v_1"),
    left_on="voltage_level1_id",
    right_index=True,
)
branches = pd.merge(
    left=branches,
    right=net.get_voltage_levels()["nominal_v"].rename("nominal_v_2"),
    left_on="voltage_level2_id",
    right_index=True,
)
branches["i1"] = (
    branches["p1"] / (branches["nominal_v_1"] * math.sqrt(3) * 1e-3)
).abs()
branches["i2"] = (
    branches["p2"] / (branches["nominal_v_2"] * math.sqrt(3) * 1e-3)
).abs()
del branches["nominal_v_1"]
del branches["nominal_v_2"]

[vidaldid-rte]

It makes sense since I is estimated in DC Security Analysis to compute volations.
However for consitency it should use the same formula as the one used in the ClosedBranchDcCurrent equation, that uses the DCPowerFactor parameter (definition at https://powsybl.readthedocs.io/projects/powsybl-core/en/latest/simulation/loadflow/configuration.html) - which 1 by default, by the way, and not sqrt(3) and accounts for some non null average reactive power.