Examples of GIC calculation

1. GICs due to an ionospheric sheet current

Assume that an eastward ionospheric sheet current flows at a height of 110 km. The width of the uniform sheet is 400 km, and its centre is approximately above the northernmost transformers (of the old 1978-79 Finnish 400 kV power system). The amplitude of the current is normalized so that the average electric field is 1 V/km in the area of the power system.

Absolute values of the earthing currents are shown as histograms:

As expected, GICs are largest under the ionospheric current.

The original output of the program is on another page.

2. Effect of the direction of a constant electric field

Assume now that the electric field has a constant magnitude of 1 V/km in the grid area. Let the direction of the field vary, and calculate GICs for each direction. The figure below shows the direction of the electric field causing the largest GIC at each station. Especially the "corner effect" is clear.