[bug] Can not read-in Matpower file with various voltage levels

[Paulnkk]

Bug report checklis

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• Browse the tutorials and tests for usefull code snippets and examples of use

• Reproduced the issue after updating with pip install --upgrade pandapower (or git pull)

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Reproducible Example

# Convert MATPOWER case to pandapower network
# mat_file_path is file to the 14-IEEE case
net = pc.from_mpc(
        mat_file_path, f_hz=50, casename_mpc_file="mpc", validate_conversion=False
    )
# Run power flow to calculate the Ybus matrix
pp.runpp(net)

Issue Description and Traceback

Hey,

in the context of the following issue: #2338, I tried to transform the following .m-file from https://github.com/MATPOWER/matpower/blob/master/data/case14.m into a pandapower format but here I got the error message from #2338. Technically the issue mainly arises from the fact that net.bus["vn_kv"] is 0 for each bus. When I read-in the adjusted 14 IEEE case which is built-in pandapower with net = pn.case14(), the net.bus["vn_kv"] includes the actual values. How can I resolve this issue ?

Thanks and best

Paul-Niklas

Expected Behavior

I should get a pandapower file which contains values similar to the built-in 14 bus case from net = pn.case14()

Installed Versions

• python version: 3.10 pandas version: 2.2.2 networkx version: 3.3 scipy version: 1.13.1 numpy version: 1.26.4 packaging version: * tqdm version: 4.66.5 deepdiff version: - Operating System name/version: macos Monterrey M1

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[Paulnkk]

Edit: I receive similar issues when I try to read-in the following cases:

https://github.com/MATPOWER/matpower/blob/master/data/case39.m and https://github.com/MATPOWER/matpower/blob/master/data/case57.m

Update:
Those cases do not work as well:
https://github.com/MATPOWER/matpower/blob/master/data/case12da.m
https://github.com/MATPOWER/matpower/blob/master/data/case15da.m