MatLab package for calculating GIC

Calculation of GICs in a power system is conveniently done in two steps:

  1. Estimate (or measure) the horizontal geoelectric field.
  2. Calculate GICs produced by this electric field external to the power system. Assume that the geometry, galvanic connections and resistances of the grid are known.
A collection of MatLab routines has been written at FMI/GEO to perform these steps. The flow of operation is as follows:

  1. In an ASCII file locations of transformers, their names, resistances and power line resistances are given in a certain format.
  2. Give the geoelectric field in a regular rectangular grid covering the power system (i.e. give it as a matrix). If measured field is available it can be used, but generally theoretical models are applied in this step. It is also possible to give the electric field as a time series. The electric field needs not be curl-free. This is essential, because the natural field seldom is curl-free.
  3. Calculate voltages between stations (= nodes, earthing points) as line integrals along transmission lines. Lines between nodes are assumed to be straight. To model a geometrically complex line, fictitious earthing points with infinite earthing resistances can be added to construct the line of shorter pieces.
  4. Calculate GICs at stations solving a linear set of equations. Then compute transmission line currents using linear expressions including earthing currents.
A simple example is presented on a separate page.

The present version is written in MatLab 4.2a, and run mainly in Macintosh Quadra 700. A typical run takes some tens of seconds in this computer (with about 50 nodes). Selection of MatLab also allows for using other platforms. The code is immediately portable.

The number of nodes can be arbitrary as long as matrix computations are possible in a computer. More exactly, if N is the number of nodes then NxN matrixes are used. Large power systems with hundreds of nodes can be divided into smaller parts without loosing accuracy. For example, the Finnish power system is treated independently of the power systems of neighbour countries (their effects are included as equivalents resistances at border stations).

The simple structure of the program and its efficiency allow for performing complex simulations and time series calculations. An example is shown on a separate page.