Differential Magnetometer Measurements of Geomagnetically Induced Currents in a Complex High Voltage Network. Issue 4 (6th April 2020)

• Record Type: Journal Article
• Authors: Hübert, J.; Beggan, C. D.; Richardson, G. S.; Martyn, T.; Thomson, A. W. P.
• Is Part Of: Space weather. Volume 18:Issue 4(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-04-06
• Subjects: Geomagnetically Induced Currents -- Complex HV network -- Differential Magnetometer Method; Space environment -- Periodicals; 551.509992
• DOI: 10.1029/2019SW002421
• Languages: English
• ISSNs: 1542-7390

Abstract

Abstract: Space weather poses a hazard to grounded electrical infrastructure such as high voltage (HV) transformers, through the induction of geomagnetically induced currents (GICs). Modeling GICs requires knowledge of the source magnetic field and the Earth's electrical conductivity structure, in order to calculate the geoelectric fields generated during magnetic storms, as well as knowledge of the topology of the HV network. Direct measurement of GICs at the ground neutral in substations is possible with a Hall effect probe, but such data are not widely available. To validate our HV network model, we use the differential magnetometer method (DMM) to measure GICs in the 400 kV grid of Great Britain. We present DMM measurements for the 26 August 2018 storm at a site in eastern Scotland with up to 20 A recorded. The line GIC correlates well with Hall probe measurements at a local transformer, though they differ in amplitude by an order of magnitude (a maximum of ∼ 2 A). We deployed a long‐period magnetotelluric (MT) instrument to derive the local impedance tensor which can be used to predict the geoelectric field from the recorded magnetic field. Using the MT‐derived electric field estimates, we model GICs within the network, accounting for the difference in magnitude between the DMM‐measured line currents and earth currents at the local substation. We find that the measured line and earth GICs match the expected GICs from our network model, confirming that detailed knowledge of the complex network topology and its resistance parameters is essential for accurately computing GICs. Plain Language Summary: Large geomagnetic storms create time‐varying magnetic fields, which induce secondary electric fields in the conductive Earth resulting in geomagnetically induced currents (GICs). The high voltage (HV) power transmission network is connected to the Earth at grounding points in substations. These offer a low‐resistance path for GICs to flow into the power network, potentially causing the transformers to malfunction. It is possible to directly measure GICs at substations using Hall effect probes, but due to cost and operational reasons, at present only four substations in the United Kingdom are monitored. Therefore, we have developed a new instrument to measure GICs indirectly using two magnetometers, one placed under the HV line and another a few hundred meters away. By examining the differences between the magnetometers, we work out the additional current flowing in the HV line. We compare our measurements to observations made by a Hall probe at a nearby transformer during a geomagnetic storm in August 2018. The GICs from the line measurements match the shape of the Hall probe, but there is a difference in amplitude. Further analysis shows that the amplitude differences arise from the resistance and earthing properties of the individual HV lines and transformers within the power network. Key Points: Geomagnetically induced currents are measured in high voltage lines using the differential magnetometer method Line currents are compared with measurements from a transformer Hall probe at a local substation Measurements are compared with modeled line currents from a network representation