1. Recent advances and validation of GIC modelling in the UK
Gemma Richardson, Ciaran Beggan, Alan Thomson

2. Modelling GIC
Models of geomagnetically induced currents (GIC) require:
Input geomagnetic field
Electric field calculation (including ground conductivity model)
Estimation of GICs in the network
We have recently been upgrading our network and trying to validate each step in the process
Look at the three things above and the full process

3. Input geomagnetic field
How does distance from observatory affects GIC estimates?
Use Spherical Elementary Current Systems (SECS) to interpolate magnetic field
Compare with using data from individual observatories across the whole grid

4. Input geomagnetic field
Results shown for October 2003 storm
Observatories within the network, or on the same geomagnetic latitude within 400km gave estimates within 25% on average with correlation >0.8
More distant observatories become less reliable, for example experiencing max GIC at different times

5. Electric field calculation
Measurements
We have electric field measurements at the three UK observatories
10Hz
Probes ~100m apart in NS and EW directions
Conductivity model using data from airborne geophysical surveys of UK and associating with geology from the 86 lithologies using UK geological map
And 10km grid
So we will obviously not have the local detail that will be included in the measurements – but during a storm when regional signal is larger we would hopefully get a bit of a match

6. Electric field calculation
Model
Thin-sheet model
The conductivity model of top 3km based on UK lithologies and bathymetry
10km grid
Anomalous conductance

7. Electric field
Measured (blue) and modelled (red) E at 1 minute resolution
With a 10minute moving average on the measured data to smooth it (used 10minutes for E calculation)
Not included Lerwick as its so far off the model anyway
Hartland still very affected by tidal signal – will look at removing that this week
Overestimate hartland Y particularly – still need to to a lot of work on understanding local effects
Correlation NS : 0.43
EW : 0.43
Correlation NS : 0.04
EW : 0.29

8. Electric field
We need to account for local effects better, e.g. galvanic distortion, tidal signals, local conductivity etc. (see poster 5 – Baillie et al.)
More storms will help
During the SWIGS project (see Poster 4 – Thomson et al.) we will measure E-fields at more sites in the UK so we can also test the model away from the observatories

9. GIC calculation
Horton et al 2012 (IEEE Transactions on power delivery, 27) provides a test grid and calculated GIC for a uniform electric field
Mix of transformer types, single and parallel connections and blocking devices

10. Comparison
Despite some differences in the method we get results which are consistent with the Horton paper
Horton et al. (2012)
BGS
North
East
Sub1
0.00
Sub2
115.63
114.25
Sub3
139.85
137.87
Sub4
19.98
19.22
Sub5
-65.46
-63.94
Sub6
-57.29
354.52
-53.24
353.99
Sub7
Sub8
60.90
134.30
62.45
134.14
We use a more sophisticated approach for getting the voltage - they just do V = E_N*L_N + E_E*L_E - which is fine here as E is constant.
We use nodal admittance method -
The root-mean-square differences is 2.3 A for the North direction and 0.7 A for the East direction
Per transformer we the difference was <1A per phase for all but 3 transformers and they were all <2A

11. Power network upgrade
Network upgrade using data from the 2016 Electricity Ten Year Statement
Better representation of substation nodes
Better inclusion of parallel lines

12. Comparsion with GIC measurements
Correlation
0.469
0.448
0.503
0.615
Quite an underestimate at Strathaven – which is odd – with the EURISGIC grid Strathaven was pretty good I think. I tried changing the way the grounding is done at this one site (as it was one with separate earthing mats) but it didn’t make much difference. I’m not sure whether changing that for all the sites will change anything
Maybe Strathaven is related to the e-field underestimating Esk?
Hartland E isn’t great but its far from these particular sites

13. Summary Electric field on a broad scale we capture the storm
need to account for local effects better to truly compare the model and measured data
Future work will help with validation across the UK
Validated GIC calculation
Full GIC calculation
Getting the size and timing of GIC largely correct although these are relatively small GIC measurements
SWIGS project will really help with validation – providing more measurements of both E and GIC

15. Ler – Mar 2015

16. Had - unfiltered
0.1406
0.0314

17. Sep 2017 – E-field

18. Sep 2017 - GIC correlation HUNT 0.5343286546782464
correlation NEIL
correlation STRA
correlation TORN

19. Mar2015 resampled to 1min means