Determination of ground conductivity and system parameters for optimal modeling of geomagnetically induced current flow in technological systems

Abstract

In this work, methods to determine technological system parameters and the ground conductivity structure from different sets of geomagnetically induced current (GIC), magnetic field and geoelectric field observations are explored. The goal of the work is to enable optimal modeling of induced currents in any technological system experiencing GIC. As an additional product, the introduced methods can also be applied to utilize GIC observations in the imaging of the subsurface geological structures. Here a robust processing scheme and Occam's inversion technique familiar from magnetotelluric (MT) studies are applied to the determination of the ground conductivity structure. The application of the methods to GIC data from the Finnish pipeline for a storm period of October 24-November 1, 2003 demonstrate that optimal system parameters and ground conductivity structure can be obtained using time series comprising only 8 days worth of data. Importantly, the obtained ground model is in agreement with models obtained in earlier MT studies. Furthermore, it is shown that although in an ideal case the magnetic field data used should be obtained from the immediate vicinity of the GIC observation site, some spatial separation (200-300 km) between the sites can be tolerated.

Geomagnetically induced currents in a power grid of northeastern Spain

“…The ratio c t = b t /a t is equal to À1.18. This ratio can be obtained directly from the measured ground geomagnetic variations [Pulkkinen et al, 2007]:…”

Electromagnetic Source Equivalence and Extension of the Complex Image Method for Geophysical Applications

“…Accordingly, the corresponding requirement for R n to be negligible for the point source is p − 1 pk 2 h. In a typical geophysical setting the source is located in the ionosphere at the height of about 110 km and one is interested in periods of about 1-1000 seconds. Then by using the plane wave surface impedance derived for southern Finland by [21], one can estimate the magnitudes of p − 1 pk 2 and |p| and compare them to the height h of the source. For the relatively long periods associated with geophysical signals p − 1 pk 2 is several orders of magnitude larger than 110 km.…”

“…(63) and (64) and (64). The fields were evaluated on the ground by using the period of 100 s, I = 10 6 A, h = 110 km, the vacuum permeability and the plane wave surface impedance derived for southern Finland by [21]. the fields were evaluated by using the period of 100 s, I = 10 6 A, h = 110 km, the vacuum permeability and the plane wave surface impedance derived for southern Finland by [21].…”

“…The current loop having amplitude of I = 10 6 A is closed in the infinity. Again, layered ground model derived for southern Finland by [21] was used in the calculations. The total electromagnetic field generated by the external current system was computed on the ground at z = 0 for the period of 100 s using both the extended CIM as described above and the exact formulation by [18].…”

“…However, in geophysical situations a homogeneous ground is often not a very good approximation, and the usage of a layered ground enables a more accurate inclusion of the wide frequency band associated with the geomagnetic induction (e.g., [21]). Thus, it is of interest to formulate CIM in a way that allows for the usage of layered ground structures, as in the works by [22] and [17].…”