Power-flow study

In power engineering, a power-flow study is a numerical analysis of the flow of electric power in an interconnected system. It is also known as power-flow analysis, load-flow study or load-flow analysis, with or without the hyphen. It analyzes the power systems in normal steady-state operation and may analyze the system’s capability to adequately supply the connected load. The principal information obtained from the power-flow study is the magnitude and phase angle of the voltage at each bus, and the real power and reactive power flowing in each line. The total system losses and individual line losses are also tabulated. A power-flow study usually uses simplified notations such as a one-line diagram and per-unit system.

In terms of its approach to uncertainties, power-flow study can be divided to deterministic power-flow study and uncertainty-concerned power-flow study. Deterministic power-flow study does not take into account the uncertainties arising from both power generations and load behaviors. To take the uncertainties into consideration, there are several approaches that has been used such as probabilistic, possibilistic, information gap decision theory, robust optimization, and interval analysis.

Performing a power-flow study on an existing system provides insight and recommendations as to the system operation and optimization of control settings to obtain maximum capacity while minimizing the operating costs. Power-flow studies are important for planning future expansion of power systems as well as in determining the best operation of existing systems, especially for the optimal operations of groups of generating units. A power-flow study is especially valuable for a system with multiple load centers, such as a refinery complex.

Commercial power systems are usually too complex to allow for hand solution of the power flow. Special-purpose network analyzers were built between 1929 and the early 1960s to provide laboratory-scale physical models of power systems. Large-scale digital computers replaced the analog methods with numerical solutions.

In addition to a power-flow study, computer programs perform related calculations such as short-circuit fault analysis, stability studies (transient and steady-state), unit commitment and economic dispatch. In particular, some programs use linear programming to find the optimal power flow, the conditions which give the lowest cost per kilowatt hour delivered.