Load flow study is an important tool involving numerical analysis applied to a power system. Unlike traditional circuit analysis, a load flow study usually uses simplified notation such as a one-line diagram and per-unit system, and focuses on various forms of AC power (i.e.: reactive, real, and apparent) rather than voltage and current. There exist a number of software implementations of power flow studies.

In addition to a load flow study itself, sometimes called the base case, PSS performs other types of analysis, such as fault analysis and economic analysis. In particular, we use linear programming to find the optimal power flow, the conditions which give the lowest cost per kW generated.

The great importance of load flow studies is in planning the future expansion of power systems as well as in determining the best operation of existing systems. The principal information obtained from the load flow study is the magnitude and phase angle of the voltage at each bus and the real and reactive power flowing in each line.