Telluric Currents: A Meeting of Theory and Observation

Abstract

Pipe-to-soil (P/S) potential variations resulting from telluric currents have been observed on pipelines in many locations.However, it has never been clear which parts of a pipeline will experience the worst effects. Two studies were conducted to answer this question. Distributed-source transmission line (DSTL) theory was applied to the problem of modeling geomagnetic induction in pipelines. This theory predicted that the largest P/S potential variations would occur at the ends of the pipeline. The theory also predicted that large P/S potential variations, of opposite sign, should occur on either side of an insulating flange. Independently, an observation program was conducted to determine the change in telluric current P/S potential variations and to design counteractive measures along a pipeline in northern Canada. Observations showed that the amplitude of P/S potential fluctuations had maxima at the northern and southern ends of the pipeline. A further set of recordings around an insulating flange showed large P/S potential variations, of opposite sign, on either side of the flange. Agreement between the observations and theoretical predictions was remarkable. While the observations confirmed the theory, the theory explains how P/S potential variations are produced by telluric currents and provides the basis for design of cathodic protection systems for pipelines that can counteract any adverse telluric effects.

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“…[17] The trends in the effective impedance curves are consistent with the E/B ratio given by Campbell [1986] and Pirjola [1982] and the 180°phase difference is consistent with PSP signals on either side of a pipeline insulating joint [Boteler and Seager, 1998]. The order of magnitude difference between the effective impedance curves for different PSP sites on a pipeline may be due to the distance between grounding points, or pipeline orientation with respect to the source fields.…”

“…Similar studies have also been conducted in the Tierra del Fuego region of South America [Osella et al, 1998;Osella and Favetto, 2000]. Large GICs have been correlated with the largest rate of change of the geomagnetic field [Viljanen, 1997;Viljanen et al, 1999;Trichtchenko and Boteler, 2004] and simulations of PSPs on Canadian and Scandinavian pipelines have also been conducted [Boteler and Seager, 1998;Pulkkinen et al, 2001b;Trichtchenko and Boteler, 2002;Fernberg et al, 2007]. GIC signals observed on low-latitude pipelines [Martin, 1993;Waters et al, 2006] are likely to have different ionospheric source fields to those observed on high-latitude pipelines and provide additional spectral information for comparison with model predictions.…”

“…The first step is to determine the geoelectric field and the next step involves applying the calculated geoelectric field to the engineering problem for the appropriate infrastructure. The geoelectric field has been applied to the calculation of GICs in power networks using Kirchhoff's current laws [Viljanen and Pirjola, 1994a] and Complex Image methods Viljanen et al, 1999], and to the calculation of PSPs using Distributed Source Transmission Line (DSTL) theory [Boteler and Seager, 1998;Boteler, 2000;Pulkkinen et al, 2001b;Trichtchenko and Boteler, 2002].…”

“…Further, the GIC index defined in this paper can be derived entirely from geomagnetic field data and does not require knowledge of the Earth's conductivity, ionospheric current geometry and the relevant infrastructure details required for the more accurate simulations of PSPs [Boteler and Seager, 1998;Osella et al, 1998;Favetto and Osella, 1999;Pulkkinen et al, 2001b;Trichtchenko and Boteler, 2002;Fernberg et al, 2007]. The GIC index would be an indicator of space weather activity applicable to both pipeline and power networks.…”

“…[3] Previous research in this area has identified Geomagnetic Induced Currents (GICs) as the major source of variations in the PSPs routinely recorded on long pipelines [Campbell, 1978[Campbell, , 1986Boteler and Seager, 1998]. GICs have their ultimate source in the dynamics of space weather.…”