Editing Power-flow study (section)

==Model==
An '''alternating current power-flow model''' is a model used in electrical engineering to analyze [[power grids]]. It provides a [[Nonlinear systems|nonlinear system]] of equations which describes the energy flow through each transmission line. The problem is non-linear because the power flow into load impedances is a function of the square of the applied voltages. Due to nonlinearity, in many cases the analysis of large network via AC power-flow model is not feasible, and a linear (but less accurate) DC power-flow model is used instead.

Usually analysis of a three-phase power system is simplified by assuming balanced loading of all three phases. Sinusoidal steady-state operation is assumed, with no transient changes in power flow or voltage due to load or generation changes, meaning all current and voltage waveforms are sinusoidal with no DC offset and have the same constant frequency. The previous assumption is the same as assuming the power system is linear time-invariant (even though the system of equations is nonlinear), driven by sinusoidal sources of same frequency, and operating in steady-state, which allows to use [[phasor]] analysis, another simplification. A further simplification is to use the [[per-unit system]] to represent all voltages, power flows, and impedances, scaling the actual target system values to some convenient base. A system [[one-line diagram]] is the basis to build a mathematical model of the generators, loads, buses, and transmission lines of the system, and their electrical impedances and ratings.