diff --git a/docs/user_manual/calculations.md b/docs/user_manual/calculations.md index e7bce21fe..f29e3dba8 100644 --- a/docs/user_manual/calculations.md +++ b/docs/user_manual/calculations.md @@ -216,6 +216,31 @@ Hence, they can be constructed by PGM output attributes in the following way: The `side` here can be `from`, `to` for {hoverxreftooltip}`user_manual/components:Branch`es, `1`, `2`, `3` for {hoverxreftooltip}`user_manual/components:Branch3`s. +#### Symmetric vs asymmetric calculations + +Power-grid-model can solve the grid either as a balanced single-phase equivalent (symmetric) or in full three-phase +detail (asymmetric). +The option affects which attributes are required and how results are exposed. + +- **Symmetric calculations (`symmetric=True`, default):** Assume a perfectly balanced three-phase system so every phase + shares the same voltage and current. + The solver builds a positive-sequence network using `r1`, `x1`, `c1`, … parameters and collapses any asymmetric + appliance to a single equivalent (asymmetric loads/generators are averaged across phases as described in + [Component Type Hierarchy and Graph Data Model](./data-model.md#symmetry-of-components-and-calculation)). + Output returns single values and voltages are line-to-line voltage magnitudes. +- **Asymmetric calculations (`symmetric=False` or any non-three-phase fault):** Builds a full $abc$ nodal admittance + matrix and solves each phase separately. + Next to the positive-sequence parameters, the model now also needs the zero-sequence parameters (e.g. `r0`, `x0`, + `c0`), or per-phase parameters (`r_matrix` & `x_matrix`) for `asym_line`; symmetric components are expanded by evenly + splitting their totals across the three phases. + Output returns arrays with values per phase and voltages are line-to-neutral voltage magnitudes. + +```{note} +For short-circuit calculations, a three-phase `fault_type` is calculated with a symmetric calculation, while any other +`fault_type` (e.g. single- or two-phase faults) automatically triggers the asymmetric calculation. +Outputs for short circuit calculations are always giving asymmetric output, independent of the fault type present. +``` + ### Power flow algorithms Two types of power flow algorithms are implemented in power-grid-model; iterative algorithms (Newton-Raphson / Iterative