  Constructing a power network model for geomagnetically induced current (GIC)
calculations requires information on the DC resistances of elements within a
network. This information is often not known, and power network models are
simplified as a result, with assumptions used for network element resistances.
Ireland's relatively small, isolated network presents an opportunity to model a
complete power network in detail, using as much real-world information as
possible. A complete model of the Irish 400, 275, 220 and 110 kV network was
made for GIC calculations, with detailed information on the number, type and DC
resistances of transformers. The measured grounding resistances at a number of
substations were also included in the model, which represents a considerable
improvement on previous models of the Irish power network for GIC calculations.
Sensitivity tests were performed to show how calculated GIC amplitudes are
affected by different aspects of the model. These tests investigated: (1) How
the orientation of a uniform electric field affects GICs. (2) The effect of
including/omitting lower-voltage elements of the power network. (3) How the
substation grounding resistances assumptions affected GIC values. It was found
that changing the grounding resistance value had a considerable effect on
calculated GICs at some substations, and no discernible effect at others.
Finally, five recent geomagnetic storm events were simulated in the network. It
was found that heavy rainfall prior to the 26-28 August 2015 geomagnetic storm
event may have had a measurable impact on measured GIC amplitudes at a 400/220
kV transformer ground.
