Calculation of GIC

A theoretical calculation of GIC in a given network (power grid, pipeline etc.) is conveniently divided into two steps:

  1. "Geophysical step": Calculate the geoelectric field created primarily by ionospheric-magnetospheric currents and affected secondarily by the earth's conductivity distribution.
  2. "Engineering step": Calculate the currents produced by the geoelectric field in the circuit system constituted by the network and its earthings.

The geophysical step is generally more difficult, partly because the space and geophysical input parameters are not well known.The complex image method (CIM) (see list of publications) allows for a fast computation.

In the engineering step two different cases may be separated: a discretely-earthed network (like a power system earthed at transformers), and a continuously-earthed network (like a buried pipeline earthed through the coating). Formulas for considering the former case were derived at FMI/GEO in the 1980's. The distributed-source transmission line (DSTL) theory recently investigated and extended in connection with the collaborative project between Gasum Oy and FMI/GEO makes the treatment of a pipeline possible.