MIST
Magnetosphere, Ionosphere and Solar-Terrestrial
Assessing the Impact of Weak and Moderate Geomagnetic Storms on UK Power Station Transformers
By Zoë Lewis (Imperial College London)
Geomagnetically induced currents (GICs) are known to cause damage to power station transformers, as they can flow through the grounded neutral and generate extra magnetic flux, causing localised heating. This heating can break down the insulation and cooling oil that surrounds the core, so can be measured through small changes in the concentrations of dissolved gases within the oil.
In this work, we analysed dissolved gas data from 13 UK based transformers during geomagnetic storms from 2010-2015. We used a list of storms outlined in [1] and looked for an increase in the levels of carbon monoxide, hydrogen, and methane at the onset of the storm, as well as any correlation between the rate of gas increase and the SYM-H index. We also used the Low Energy Degradation Triangle (LEDT) method [2] as a measure of degradation.
Figure 1 shows the results of a superposed epoch analysis (SEA) for carbon monoxide, methane and hydrogen in one transformer. The epochs are centred on the start of the main phase of each storm, as defined in [1]. There is no systematic increase in the gas concentrations at the storm onset or in the following days. The interquartile range (shaded blue) is also very large owing to the highly variable data.
We conclude that during this period, the transformers studied were unaffected by space weather events. However, it is noted that 2010-2015 lies within a relatively quiet solar cycle, and there were no storms in this period that would be considered large on the scale of the past few decades. Therefore, in future work it would be desirable to expand this study to look at a more geomagnetically active period.
[1] Walach, M. T., & Grocott, A. (2019). SuperDARN Observations During Geomagnetic Storms, Geomagnetically Active Times, and Enhanced Solar Wind Driving. Journal of Geophysical Research: Space Physics, 124 (7), 5828–5847. doi: 10.1029/2019JA026816
[2] Moodley, N., & Gaunt, C. T. (2017). Low Energy Degradation Triangle for power transformer health assessment. IEEE Transactions on Dielectrics and Electrical Insulation, 24 (1), 639–646. doi: 10.1109/TDEI.2016.006042
Please see paper for full details: , , , & (2022). Assessing the impact of weak and moderate geomagnetic storms on UK power station transformers. Space Weather, 20, e2021SW003021. https://doi.org/10.1029/2021SW003021