openego / eDisGo / 39956436107

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Option to choose the cheaper measure for voltage issues: split the feeder or reinforce the path (#791)

* fix: reinforce all line segments on path to critical node

reinforce_lines_voltage_issues() determines the node at two thirds of the
feeder length (node_2_3) and normally disconnects the line there and
reconnects it to the station. If node_2_3 turns out to be the feeder
representative - the bus directly connected to the station - no line can
be disconnected and the measure falls back to reinforcing lines instead.

In that fallback only the single line between the station and the
representative was reinforced, not the remaining lines on the path to the
critical node. Since the voltage deviation at the critical node is
generally dominated by the segments further away from the station, the
measure frequently did not change the reported voltage issue at all. Grid
reinforcement then repeated the same ineffective measure in every
iteration and aborted with MaximumIterationError, typically reporting a
residual deviation in the per mille range.

LVGrid_5 of the test grid shows this: for a voltage issue at
Bus_BranchTee_LVGrid_5_2, node_2_3 is moved back to the representative
Bus_BranchTee_LVGrid_5_1. Only Line_50000003 was reinforced, which is
0.56 m long, while Line_50000002 - 30 m of NAYY 4x1x35 causing nearly all
of the voltage drop - was left untouched.

All lines on the path from the station to the critical node are now
reinforced. Feeders consisting of a single line are unaffected.

Short feeders are affected most, which is why the error shows up
predominantly in grids that went through spatial complexity reduction,
where node_2_3 frequently coincides with the representative.

Test expectations for the number of equipment changes and grid expansion
costs are updated accordingly, as more lines are reinforced per measure.

* fix: reinforce lines with largest resistance reduction on path

When node_2_3 is the feeder representative, no line can be disco... (continued)

50 of 52 new or added lines in 2 files covered. (96.15%)

9824 of 11439 relevant lines covered (85.88%)

0.86 hits per line