Tim Divett
I am a postdoctoral research fellow in the physics department at the University of Otago, researching the effect of space weather on electrical grids through geomagnetically induced currents (GIC). I am working with Craig Rodger at the University of Otago, Malcolm Ingham at Victoria University of Wellington, Allan Thomson, Ciaran Beggan, Gemma Richardson, and Ellen Clarke at the British Geological Survey developing models of the geoelectric field and electrical transmission network in New Zealand.
My PhD was about optimising arrangement and tuning of large arrays of tidal stream turbines within tidal channels. This required modelling and understanding the fluid flow structures ranging from oceanographic drivers of the channel dynamics to the interaction of wakes from individual turbines. My PhD was through the University of Otago's Ocean Physics Group and NIWA's Marine Physics Group, supervised by Ross Vennell and Craig Stevens.
I have used a range of numerical modelling and data analysis techniques to explore applied energy projects. These projects range from thermodynamic modelling and analysis of long term field measurements for building energy efficiency projects to further tidal energy research.
Supervisors: Prof. Craig Rodger (GIC), Assoc. Prof. Ross Vennell (tidal energy), Assoc. Prof. Craig Stevens (tidal energy), and Dr Inga Smith (building energy projects)
Phone: +64 (0)3 4771677
Address: Deparment of Physics
University of Otago
PO Box 56
Dunedin
New Zealand
My PhD was about optimising arrangement and tuning of large arrays of tidal stream turbines within tidal channels. This required modelling and understanding the fluid flow structures ranging from oceanographic drivers of the channel dynamics to the interaction of wakes from individual turbines. My PhD was through the University of Otago's Ocean Physics Group and NIWA's Marine Physics Group, supervised by Ross Vennell and Craig Stevens.
I have used a range of numerical modelling and data analysis techniques to explore applied energy projects. These projects range from thermodynamic modelling and analysis of long term field measurements for building energy efficiency projects to further tidal energy research.
Supervisors: Prof. Craig Rodger (GIC), Assoc. Prof. Ross Vennell (tidal energy), Assoc. Prof. Craig Stevens (tidal energy), and Dr Inga Smith (building energy projects)
Phone: +64 (0)3 4771677
Address: Deparment of Physics
University of Otago
PO Box 56
Dunedin
New Zealand
less
Related Authors
InterestsView All (14)
Uploads
Papers by Tim Divett
be induced in high voltage transmission networks, damaging individual transformers
within substations. A common approach to modeling a transmission
network has been to assume that every substation can be represented by a
single resistance to Earth. We have extended that model by building a transformerlevel
network representation of New Zealand’s South Island transmission network.
We represent every transformer winding at each earthed substation
in the network by its known DC resistance. Using this network representation
significantly changes the GIC hazard assessment, compared to assessments
based on the earlier assumption. Further, we have calculated the GIC
flowing through a single phase of every individual transformer winding in the
network. These transformer-level GIC calculations show variation in GICs
between transformers within a substation due to transformer characteristics
and connections. The transformer-level GIC calculations alter the hazard assessment
by up to an order of magnitude in some places. In most cases the
calculated GIC variations match measured variations in GIC flowing through
the same transformers. This comparison with an extensive set of observations
demonstrates the importance of transformer-level GIC calculations in
models used for hazard assessment.
be induced in high voltage transmission networks, damaging individual transformers
within substations. A common approach to modeling a transmission
network has been to assume that every substation can be represented by a
single resistance to Earth. We have extended that model by building a transformerlevel
network representation of New Zealand’s South Island transmission network.
We represent every transformer winding at each earthed substation
in the network by its known DC resistance. Using this network representation
significantly changes the GIC hazard assessment, compared to assessments
based on the earlier assumption. Further, we have calculated the GIC
flowing through a single phase of every individual transformer winding in the
network. These transformer-level GIC calculations show variation in GICs
between transformers within a substation due to transformer characteristics
and connections. The transformer-level GIC calculations alter the hazard assessment
by up to an order of magnitude in some places. In most cases the
calculated GIC variations match measured variations in GIC flowing through
the same transformers. This comparison with an extensive set of observations
demonstrates the importance of transformer-level GIC calculations in
models used for hazard assessment.
New Zealand's latitude and island setting, mean that modelling approaches successfully applied in the UK in the past can be used. However, deep water (4000 m) near the coast means even stronger spatial gradients of conductance can occur around New Zealand compared to the situation in the UK's shallow continental shelf. This strong gradient poses challenges for the thin-sheet model (of Vasseur and Weidelt) used to model the electric field as a function of magnetic field and conductance.
The NZ electrical transmission grid consists of lines carrying 220kV, 110kV and 66kV with multiple earthing nodes at each transformer substation. The relative importance of the 66kV network is explored in this study, in relation to currents induced in the higher voltage lines. Transpower have measured DC earth currents at 17 substations at selected locations in the South Island grid for up to 15 years, including through multiple transformers at the same substation. Different transformers at the same substation can experience quite different GIC during space weather events. Therefore, in this work, each transformer at each substation is modelled separately to compare directly with the measured currents. The sensitivity of induced current in the grid to the direction of an imposed electric field is also explored.
Our model will eventually be used as an operational and validated tool to explore the risk to the New Zealand grid from geomagnetic storms. Further, mitigation tactics which could be used to reduce the threat to the electrical grid will be evaluated. Ultimately this study aims to develop a modelling tool that will be used to strengthen New Zealand's grid against the risks of space weather. In particular we will focus at the transformer level where the risk lies, and not at the substation level as has been commonly done to date. As we will validate our model against the extensive Transpower observations, this will be a valuable confirmation of the approaches used by the wider international community.
geomagnetically induced currents (GIC) during geomagnetic storms, for example in November
2001. In this study we have developed an initial model of the South Island's power grid to advance
understanding of the impact of GIC on New Zealand's (NZ) grid.
NZ's latitude and island setting mean that modelling approaches successfully used in the UK in the
past can be used. Vasseur and Weidelt's thin sheet model is applied to model the electric field as a
function of magnetic field and conductance. However the 4 km deep ocean near NZ's coast
compared to the UK's relatively shallow continental shelf waters restricts the range of frequency
and spatial grid that can be used due to assumptions in the thin sheet model. Some early
consequences of these restrictions will be discussed.
Lines carrying 220kV, 110kV and 66kV make up NZ's electrical transmission grid with multiple
earthing nodes at each substation. Transpower have measured DC earth currents at 17 nodes in
NZ's South Island grid for 15 years, including observations at multiple transformers for some
substations. Different transformers at the same substation can experience quite different GIC
during space weather events. Therefore we have initially modelled each transformer in some
substations separately to compare directly with measured currents.
Ultimately this study aims to develop a validated modelling tool that will be used to strengthen NZ's
grid against the risks of space weather. Further, mitigation tactics which could be used to reduce
the threat to the electrical grid will be evaluated. In particular we will focus at the transformer level
where the risk lies, and not at the substation level as has been commonly done to date. As we will
validate our model against the extensive Transpower observations, this will be a valuable
confirmation of the approaches used by the wider international community.