 This is partly due to the increase in the interconnectedness at higher voltages, connections in terms of power transmission to grids in the auroral zone, and grids operating closer to capacity than in the past.To understand the flow of GIC in power grids and to advise on GIC risk, analysis of the quasi-DC properties of the grid is necessary.This must be coupled with a geophysical model of the Earth that provides the driving surface electric field, determined by combining time-varying ionospheric source fields and a conductivity model of the Earth.