Abstract
This thesis consists of a detailed study into geomagnetically induced currents
(GIC) in the New Zealand power network.
To estimate how geomagnetic disturbances drive GICs in the New Zealand power
network, a thin-sheet model with a conductance map of New Zealand and magnetic
field input was used to calculate the induced surface electric fields. A model of the
New Zealand power network, down to the transformer level was constructed using
data from our industry partner, Transpower. This model takes into consideration
the network resistances and connections. The model was subjected to a number of
network sensitivity tests to understand how important each factor is to the GIC calculations.
Our GIC modelling approach was also validated against a test network
from the literature.
GICs were modelled for 25 geomagnetic disturbances over a 20 year period. The
calculated GIC was then compared with a large dataset of GIC observations to identify
aspects where the model is limited. Various scaling techniques in the frequency
domain were calculated to correct for these limitations. A network scaling factor
was determined from the 73 transformers with observations. This allowed modelled
GIC at transformers with no measurements to be scaled along with those with
observations.
Using this scale factor, multiple different extreme storm scenarios with variouslatitude
varying magnetic fields were modelled. These extreme storm scenarios
hope to capture the worst-case geomagnetic storm that could occur in the future.
Between 13% and 35% of transformers reached danger level thresholds provided
by Transpower. These danger levels indicate GIC magnitudes and durations that
would likely cause stress and damage to the transformer. This indicates significant
impact to the New Zealand power network and suggests mitigation efforts should
be undertaken.
Transpower’s current mitigation method, which focuses on the lower South Island,
was tested for the extreme storm scenarios previously modelled. After promising
results, this mitigation method was extended to the whole power network. The
GIC in New Zealand was significantly decreased for this nationwide mitigation
method, however that plan was deemed unfeasible for implementation. Following
this a more targeted mitigation plan, with less impact on the power distribution
in New Zealand, was formulated in collaboration with Transpower. Despite
significantly less network modifications, the GIC at locations of most concern was
decreased by a similar amount. The total network GIC decreased by 16% and fewer
transformers reached the various danger level thresholds. This new mitigation method is currently being integrated into Transpower’s official response to large
geomagnetic disturbances.