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docs: explain phase-shifting transformers with GenericBranch#1485

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nightcityblade:fix/issue-1484
Open

docs: explain phase-shifting transformers with GenericBranch#1485
nightcityblade wants to merge 1 commit into
PowerGridModel:mainfrom
nightcityblade:fix/issue-1484

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Fixes #1484

Summary

  • document how generic_branch parameters map to a static phase-shifting transformer
  • include a finite-reactance lossless example
  • warn that an impedance-free ideal phase link is singular in the branch model

Testing

  • PATH=/Users/shensheng/.nvm/versions/node/v24.18.0/bin:$PATH uv run --frozen --group lint pre-commit run markdownlint --files docs/user_manual/components.md
  • git diff --check

The full Sphinx build could not reach the changed page locally because the generated Doxygen XML (docs/doxygen/build/xml/index.xml) is absent and Doxygen is not installed in this environment.

Signed-off-by: nightcityblade <nightcityblade@gmail.com>
@mgovers mgovers added the documentation Improvements or additions to documentation label Jul 23, 2026

@mgovers mgovers left a comment

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Hi @nightcityblade,

Thank you for your contribution! I only have one minor comment. After you've resolved that, I will kick off CI.

Comment on lines +274 to +291
#### Phase-shifting transformer

A `generic_branch` can represent a static phase-shifting transformer with finite series impedance. For the tap position
being calculated, use:

* `k` for the transformer magnitude ratio;
* `theta` for the fixed and tap-dependent phase shift, in radians;
* `r1` and `x1` for the transformer series resistance and reactance; and
* `g1` and `b1` for the magnetizing conductance and susceptance.

For example, a lossless phase-shifting transformer that still has finite series reactance can use `r1 = 0`, `x1 > 0`,
`g1 = 0`, `b1 = 0`, `k = 1`, and `theta` equal to the desired phase shift.

```{warning}
An impedance-free ideal phase link cannot be represented by setting both `r1` and `x1` to zero. The branch model uses
`1 / (r1 + j x1)` for its series admittance, so zero series impedance would make the model singular.
```

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It explains it quite well, but please move it to docs/user_manual/non-pgm-components.md and instead make a reference here to that location.

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[IMPROVEMENT] Improve documentation on how to use GenericBranch for Phase Shifting Transformer

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