The National Academy of Sciences founded The National Academies Press (NAP) with the goal of publishing reports of all four national academies. Annually, NAP publishes more than 200 books from the fields of science, engineering and medicine and offers more than 4000 titles in PDF on its website (http://www.nap.edu/) free of charge.

/pdf/the-national-academies-press-3oqc1apmt7.pdf

The National Academies Press

The effects of geomagnetic disturbances on electrical systems at the earth's surface

Abstract Geomagnetic disturbances have affected electrical systems on the ground for over 150 years. The first effects were noted on the early telegraph in the 1840s and in this century magnetic storms have caused power system blackouts and phone system outages. Affected systems include all those that use electrical conductors: whether for transmission of power or signals or where the conducting properties are incidental to their use such as with pipelines and railway tracks. In power systems geomagnetically induced currents cause partial saturation of power transformers producing transformer heating and distortion of the ac waveform leading to misoperation of relays and other equipment. On pipelines, induced currents may contribute to corrosion but also present a problem with the electrical surveys of the pipe performed to monitor the corrosion prevention systems. Severity of these effects depends on disturbance size, proximity to the auroral zone, and the conductivity structure of the Earth. Also significant are system parameters such as the use of higher resistance coatings on pipelines and the linking of power systems into larger networks. In this paper we have attempted to catalogue all the published reports of geomagnetic effects on electrical systems and show their occurrence in the context of the solar cycle and geomagnetic activity variations for the years 1844 to 1996.

The Effects of Geomagnetic Disturbances on Electrical Systems at the Earth's Surface - An Update

An efficient method allowing the transformer flux offset and exciting-current waveform to be determined for combined AC and geomagnetically induced current (GIC) excitation, without lengthy time-domain simulations, is described. This iterative approach solves for the equilibrium saturation condition using lumped-parameter nonlinear magnetic-circuit models. In addition to investigating single-phase transformer performance, the authors examine the performance of certain three-phase transformer types for which GIC results in phase imbalance. >

Characteristics of transformer exciting-current during geomagnetic disturbances

We consider geomagnetically induced currents (GICs) in power systems from the viewpoint of a geophysicist. Special attention is paid to the Finnish high-voltage power system, in which exact theoretical model calculations together with recordings have been performed for several years. We present several examples of theoretically computed GICs using different geophysical models for estimating the geoelectric field driving GICs. Statistical prediction of GICs is outlined referring to studies made in Finland. We show that a combination of GIC recordings at few sites with theoretical modelling of ionospheric currents and the earth's conductivity, and data of geomagnetic activity makes it possible to derive GIC statistics of the entire power system. Finally, we discuss requirements for a long-range prediction of GICs, which will obviously be a widely-studied topic in future.

Geomagnetically induced currents in the Finnish high-voltage power system

This paper summarizes a research effort investigating the effects of geomagnetic storms on electric power systems. Geomagnetic storms, which are caused by solar flares, can cause spurious quasi-dc currents in power systems; these are termed solar-induced-currents (SIC). A summary of SIC data recorded on over 30 power systems across the United States is presented, and power system effects are discussed. The important problem of internal localized heating in power transformers due to SIC is presented, as well as a consideration of possible methods of mitigation of the SIC.

Solar-Induced-Currents in Power Systems: Cause and Effects

Geomagnetic field fluctuations produce spurious, quasi-dc currents in power systems. The currents enter through system grounding points, and are of sufficient magnitude to cause half-cycle saturation in power transformers. These currents have been recorded and are summarized, and recommendations made in the significant problem areas of system disturbances and equipment effects due to geomagnetic storms. The major problem areas include increased VAR requirements and shifts in VAR flow, system-voltage fluctuations, generation of harmonics, protective relayiing misoperations, and possible localized internal heating in transformers. Recommendations relating to these effects have Pot been published previously.

The Effects of Geomagnetic Storms on Electrical Power Systems

Solar flares can trigger severe fluctuations in the earth's magnetic field, termed geomagnetic storms. Geomagnetic storms produce quasi-dc currents in 60 Hz electric power systems. These spurious dc currents caused tundesirable equipment and system operating effects. A moderately severe geomagnetic storm occurred on August 4, 1972. The effects of that storm on electric power systems in the continental United States and parts of Canada are documented and related to latitude, geological factors, and intensity of the recorded geomagnetic field variations.

Power System Disturbances During A K-8 Geomagnetic Storm: August 4, 1972

Physical parallels of transmission lines with communication circuits and railroad signal circuits cause induced voltages which may interfere with normal operation. Due to the demand for more efficient uses of existing rights-of-way, and to the trend toward higher line currents and voltages, such parallel problems will become more frequent and more difficult. This paper recommends a system approach to the problem in which candid discussion, mutual understanding and a willingness to adopt new techniques can benefit both utilities. New limits are discussed, new computational techniques mentioned, and the general subject of inductive coordination is covered. Shielding, protection systems and substation problems are examined.

John M. Thorson

Papers

Solar-Induced-Currents in Power Systems: Cause and Effects

The Effects of Geomagnetic Storms on Electrical Power Systems

Power System Disturbances During A K-8 Geomagnetic Storm: August 4, 1972

A System Approach to Inductive Coordination