Skip to main content
Engineering LibreTexts

5: Introduction to Load Flow

  • Page ID
    54443
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    Even though electric power networks are composed of components which are (or can be approximated to be) linear, electric power flow, real and reactive, is a nonlinear quantity. The calculation of load flow in a network is the solution to a set of nonlinear equations. The purpose of this note is to describe how network load flows may be calculated.

    This is only an elementary treatment of this problem: there is still quite a bit of activity in the professional literature concerning load flow algorithms. The reason for this is that electric utility networks are often quite large, having thousands of buses, so that the amount of computational effort required for a solution is substantial. A lot of effort goes into doing the calculation efficiently. This discussion, and the little computer program at the end of this note, uses the crudest possible algorithm for this purpose. However, for the relatively simple problems we will be doing, it should work just fine.

    • 5.1: Power Flow
      Power flow in a network is determined by the voltage at each bus of the network and the impedances of the lines between buses. Power flow into and out of each of the buses that are network terminals is the sum of power flows of all of the lines connected to that bus.
    • 5.2: Bus Admittance
      Now, if the network itself is linear, interconnections between buses and between buses and ground can all be summarized in a multiport bus impedance matrix or its inverse, the bus admittance matrix. As it turns out, the admittance matrix is easy to formulate.
    • 5.3: Gauss–Seidel Iterative Technique
      This is one of many techniques for solving the nonlinear load flow problem. It should be pointed out that this solution technique, while straightforward to use and easy to understand, has a tendency to use a lot of computation, particularly in working large problems.
    • 5.4: Example- Simple–Minded Program
      Attached to this note is a MATLAB script which will set up carry out the Gauss–Seidel procedure for networks with the simple constraints described here.
    • 5.5: Example
      Consider the system shown in Figure 1. This simple system has five buses (numbered 1 through 5) and four lines. Two of the buses are connected to generators, two to loads and bus 5 is the “swing bus”, represented as an “infinite bus”, or voltage supply.


    This page titled 5: Introduction to Load Flow is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by James Kirtley (MIT OpenCourseWare) via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.