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"]