Abstract
One of the modern applications of geomagnetism is determining the effect of geomagnetic disturbances on critical infrastructure such as power systems and pipelines. Assessing the geomagnetic hazard to such systems requires calculation of the geoelectric fields produced during geomagnetic disturbances. Such geoelectric fields can then be used as input to system models to calculate the impact on the system. This paper describes what is involved in calculating the geoelectric fields produced during real geomagnetic disturbances. The theory of geomagnetic induction is presented and used to derive the Earth transfer function relating the geoelectric and geomagnetic field variations at the Earth’s surface. It is then shown how this can be used to make practical calculations of the geoelectric fields and how the calculation process can be verified by comparison with analytic solutions obtained with synthetic geomagnetic variation data. The accuracy of the calculated geoelectric fields for geomagnetic risk assessments is limited, not by the accuracy of the calculation methods, but by the availability of geomagnetic field measurements and Earth conductivity information over the whole extent of the affected infrastructure.
Highlights
Geomagnetism has always been an applied science because of the use of the magnetic field for navigation purposes, e.g. [1] [2]
The geoelectric field can be calculated by taking a Fourier Transform of a time series of magnetic field data, multiplying the magnetic field spectral components by the Earth transfer function to obtain the electric field spectrum, and taking the inverse Fourier transform to obtain the geoelectric field in the time domain
The numerical calculation process has been verified by testing with a synthetic magnetic field time series for which an exact analytic solution of the geoelectric field is available
Summary
Geomagnetism has always been an applied science because of the use of the magnetic field for navigation purposes, e.g. [1] [2]. The telegraph was the first system to suffer from natural voltages [4], and in 1859 the “Carrington storm” caused disruption to telegraph systems around the world [5] Pipelines represent another type of long conductor subjected to geomagnetic induction. Starting in 1940, geomagnetically induced currents produced in high-voltage power transmission systems during large geomagnetic disturbances have led to equipment damage and power blackouts [8] [9] [10] [11]. Concern about these effects has led to extensive work to understand the geomagnetic effects and to assess the hazard they pose to the operation of these systems, e.g. Concern about these effects has led to extensive work to understand the geomagnetic effects and to assess the hazard they pose to the operation of these systems, e.g. [12] [13] [14]
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