[FIX] Unbalance Percent in res_bus_3ph

[furqan463]

To make it consistent with Pandapower. Currently Unbalance percent in pandapower_converter.py is V_zero / V_pos, while that defined in Pandapower is V_neg / V_pos. As per my knowledge, this is also consistent with IEC.

https://github.com/e2nIEE/pandapower/blob/develop/pandapower/results_bus.py#L71

[furqan463]

@mgovers @nitbharambe can you please review

[mgovers]

Hi @furqan463, Good find!

@nitbharambe can you please review as the EE expert?

Can we somehow validate this? I do think this change is simple enough that we don't need explicit tests but it would be interesting to think about such a test case.

[furqan463]

https://cigre-usnc.org/wp-content/uploads/2017/10/C4_Laughner.pdf

This papers refers the definitions under "Standards" section at 3.
ANSI Standard & IEEE Standards define voltage unbalance as ratio of deviation to average voltage
IEC defines voltage unbalance as ratio of negative sequence to positive sequence.

But I cannot find a reference for ratio of zero seq to positive sequence.

In Power System Protection, negative sequence is used as a measure of unbalance.

[nitbharambe]

Good find indeed @furqan463
Agreed per the IEC standard and the code at pandapower.

I think we were referring to pandapower documentation when we developed the feature which is likely incorrect:

Missed the validation part. My bad.

[furqan463]

I think we were referring to pandapower documentation

Documentation Now corrected for next release of PP.

e2nIEE/pandapower#2726