The Earth's magnetic field varies over a wide range of timescales. The longer-term variations, typically occurring over decades to millennia, are predominantly the result of dynamo action in the Earth's core. Geomagnetic variations on timescales of seconds to years also occur, due to dynamic processes in the ionosphere, magnetosphere and heliosphere. These changes are ultimately tied to variations associated with the solar activity (or sunspot) cycle and are manifestations of space weather.
The fact that the geomagnetic field does respond to solar conditions can be useful, for example, in investigating Earth structure using magnetotellurics, but it also creates a hazard. This geomagnetic hazard is primarily a risk to technology under the Earth's protective atmospheric blanket.[1]
The basic principle for the generation of GIC: variations of the ionospheric currents (I(t)) generate an electric field (E(t)) driving GIC. Shown are also real GIC recordings from the Finnish natural gas pipeline.
A time-varying magnetic field external to the Earth induces telluric currents—electric currents in the conducting ground. These currents create a secondary (internal) magnetic field. As a consequence of Faraday's law of induction, an electric field at the surface of the Earth is induced associated with time variations of the magnetic field. The surface electric field causes electrical currents, known as geomagnetically induced currents (GIC), to flow in any conducting structure, for example, a power or pipeline grid grounded in the Earth. This electric field, measured in V/km, acts as a voltage source across networks.
Examples of conducting networks are electrical power transmission grids, oil and gas pipelines, non-fiber optic undersea communication cables, non-fiber optic telephone and telegraph networks and railways. GIC are often described as being quasi direct current (DC), although the variation frequency of GIC is governed by the time variation of the electric field. For GIC to be a hazard to technology, the current has to be of a magnitude and occurrence frequency that makes the equipment susceptible to either immediate or cumulative damage. The size of the GIC in any network is governed by the electrical properties and the topology of the network. The largest magnetospheric-ionospheric current variations, resulting in the largest external magnetic field variations, occur during geomagnetic storms and it is then that the largest GIC occur. Significant variation periods are typically from seconds to about an hour, so the induction process involves the upper mantle and lithosphere. Since the largest magnetic field variations are observed at higher magnetic latitudes, GIC have been regularly measured in Canadian, Finnish and Scandinavian power grids and pipelines since the 1970s. GIC of tens to hundreds of amperes have been recorded. GIC have also been recorded at mid-latitudes during major storms. There may even be a risk to low latitude areas, especially during a storm commencing suddenly because of the high, short-period rate of change of the field that occurs on the day side of the Earth.
GIC were first observed on the emerging electric telegraph network in 1847–8 during Solar cycle 9.[2] Technological change and the growth of conducting networks have made the significance of GIC greater in modern society. The technical considerations for undersea cables, telephone and telegraph networks and railways are similar. Fewer problems have been reported in the open literature, about these systems because efforts have been made to ensure resiliency.[3]
In power grids
Modern electric power transmission systems consist of generating plants inter-connected by electrical circuits that operate at fixed transmission voltages controlled at substations. The grid voltages employed are largely dependent on the path length between these substations and 200-700 kV system voltages are common. There is a trend towards using higher voltages and lower line resistances to reduce transmission losses over longer and longer path lengths. Low line resistances produce a situation favourable to the flow of GIC. Power transformers have a magnetic circuit that is disrupted by the quasi-DC GIC: the field produced by the GIC offsets the operating point of the magnetic circuit and the transformer may go into half-cycle saturation. This produces harmonics in the AC waveform, localised heating and leads to higher reactive power demands, inefficient power transmission and possible mis-operation of protective measures. Balancing the network in such situations requires significant additional reactive power capacity.[4] The magnitude of GIC that will cause significant problems to transformers varies with transformer type. Modern industry practice is to specify GIC tolerance levels on new transformers.
On 13 March 1989, a severe geomagnetic storm caused the collapse of the Hydro-Québec power grid in a matter of seconds as equipment protective relays tripped in a cascading sequence of events.[5] Six million people were left without power for nine hours, with significant economic loss. Since 1989, power companies in North America, the United Kingdom, Northern Europe, and elsewhere have invested in evaluating the GIC risk and in developing mitigation strategies.
GIC risk can, to some extent, be reduced by capacitor blocking systems, maintenance schedule changes, additional on-demand generating capacity, and ultimately, load shedding. These options are expensive and sometimes impractical. The continued growth of high voltage power networks results in higher risk. This is partly due to the increase in the interconnectedness at higher voltages, connections in terms of power transmission to grids in the auroral zone, and grids operating closer to capacity than in the past.
To understand the flow of GIC in power grids and to advise on GIC risk, analysis of the quasi-DC properties of the grid is necessary.[6] This must be coupled with a geophysical model of the Earth that provides the driving surface electric field, determined by combining time-varying ionospheric source fields and a conductivity model of the Earth. Such analyses have been performed for North America, the UK and in Northern Europe. The complexity of power grids, the source ionospheric current systems and the 3D ground conductivity make an accurate analysis difficult.[7] By being able to analyze major storms and their consequences we can build a picture of the weak spots in a transmission system and run hypothetical event scenarios.
Grid management is also aided by space weather forecasts of major geomagnetic storms. This allows for mitigation strategies to be implemented. Solar observations provide a one- to three-day warning of an Earthbound coronal mass ejection (CME), depending on CME speed. Following this, detection of the solar wind shock that precedes the CME in the solar wind, by spacecraft at the L1Lagrangian point, gives a definite 20 to 60 minutes warning of a geomagnetic storm (again depending on local solar wind speed). It takes approximately two to three days after a CME launches from the Sun for a geomagnetic storm to reach Earth and to affect the Earth's geomagnetic field.[8]
GIC hazard in pipelines
Schematic illustration of the cathodic protection system used to protect pipeline from corrosion.
Major pipeline networks exist at all latitudes and many systems are on a continental scale. Pipeline networks are constructed from steel to contain high-pressure liquid or gas and have corrosion resistant coatings. Damage to the pipeline coating can result in the steel being exposed to the soil or water possibly causing localised corrosion. If the pipeline is buried, cathodic protection is used to minimise corrosion by maintaining the steel at a negative potential with respect to the ground. The operating potential is determined from the electro-chemical properties of the soil and Earth in the vicinity of the pipeline. The GIC hazard to pipelines is that GIC cause swings in the pipe-to-soil potential, increasing the rate of corrosion during major geomagnetic storms.[9] GIC risk is not a risk of catastrophic failure, but a reduced service life of the pipeline.
Pipeline networks are modeled in a similar manner to power grids, for example through distributed source transmission line models that provide the pipe-to-soil potential at any point along the pipe [10] (Boteler, 1997). These models need to consider complicated pipeline topologies, including bends and branches, as well as electrical insulators (or flanges) that electrically isolate different sections. From a detailed knowledge of the pipeline response to GIC, pipeline engineers can understand the behaviour of the cathodic protection system even during a geomagnetic storm, when pipeline surveying and maintenance may be suspended.
Bolduc, L., GIC observations and studies in the Hydro-Québec power system. J. Atmos. Sol. Terr. Phys., 64(16), 1793–1802, 2002.
Boteler, D. H., Distributed source transmission line theory for electromagnetic induction studies. In Supplement of the Proceedings of the 12th International Zurich Symposium and Technical Exhibition on Electromagnetic Compatibility. pp.401–408, 1997.
Boteler, D. H., Pirjola, R. J. and Nevanlinna, H., The effects of geomagnetic disturbances on electrical systems at the Earth's surface. Adv. Space. Res., 22(1), 17-27, 1998.
Erinmez, I. A., Kappenman, J. G. and Radasky, W. A., Management of the geomagnetically induced current risks on the national grid company's electric power transmission system. J. Atmos. Sol. Terr. Phys., 64(5-6), 743-756, 2002.
Lanzerotti, L. J., Space weather effects on technologies. In Song, P., Singer, H. J., Siscoe, G. L. (eds.), Space Weather. American Geophysical Union, Geophysical Monograph, 125, pp.11–22, 2001.
Lehtinen, M., and R. Pirjola, Currents produced in earthed conductor networks by geomagnetically-induced electric fields, Annales Geophysicae, 3, 4, 479-484, 1985.
Pirjola, R., Kauristie, K., Lappalainen, H. and Viljanen, A. and Pulkkinen A., Space weather risk. AGU Space Weather, 3, S02A02, doi:10.1029/2004SW000112, 2005.
Thomson, A. W. P., A. J. McKay, E. Clarke, and S. J. Reay, Surface electric fields and geomagnetically induced currents in the Scottish Power grid during the 30 October 2003 geomagnetic storm, AGU Space Weather, 3, S11002, doi:10.1029/2005SW000156, 2005.
Pulkkinen, A. Geomagnetic Induction During Highly Disturbed Space Weather Conditions: Studies of Ground Effects, PhD thesis, University of Helsinki, 2003. (available at eThesis)Archived 2013-05-27 at the Wayback Machine
In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force (EMF) across any other coils wound around the same core. Electrical energy can be transferred between separate coils without a metallic (conductive) connection between the two circuits. Faraday's law of induction, discovered in 1831, describes the induced voltage effect in any coil due to a changing magnetic flux encircled by the coil.
Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines that facilitate this movement form a transmission network. This is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as electric power distribution. The combined transmission and distribution network is part of electricity delivery, known as the electrical grid.
In electrical engineering, two conductors are said to be inductively coupled or magnetically coupled when they are configured in a way such that change in current through one wire induces a voltage across the ends of the other wire through electromagnetic induction. A changing current through the first wire creates a changing magnetic field around it by Ampere's circuital law. The changing magnetic field induces an electromotive force (EMF) voltage in the second wire by Faraday's law of induction. The amount of inductive coupling between two conductors is measured by their mutual inductance.
Space weather is a branch of space physics and aeronomy, or heliophysics, concerned with the varying conditions within the Solar System and its heliosphere. This includes the effects of the solar wind, especially on the Earth's magnetosphere, ionosphere, thermosphere, and exosphere. Though physically distinct, space weather is analogous to the terrestrial weather of Earth's atmosphere. The term "space weather" was first used in the 1950s and popularized in the 1990s. Later, it prompted research into "space climate", the large-scale and long-term patterns of space weather.
Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic field is generated by electric currents due to the motion of convection currents of a mixture of molten iron and nickel in Earth's outer core: these convection currents are caused by heat escaping from the core, a natural process called a geodynamo.
A geomagnetic storm, also known as a magnetic storm, is a temporary disturbance of the Earth's magnetosphere caused by a solar wind shock wave.
A balun is an electrical device that allows balanced and unbalanced lines to be interfaced without disturbing the impedance arrangement of either line. A balun can take many forms and may include devices that also transform impedances but need not do so. Sometimes, in the case of transformer baluns, they use magnetic coupling but need not do so. Common-mode chokes are also used as baluns and work by eliminating, rather than rejecting, common mode signals.
A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through several substations at different voltage levels. A substation may include transformers to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages. They are a common component of the infrastructure. There are 55,000 substations in the United States.
Single-wire earth return (SWER) or single-wire ground return is a single-wire transmission line which supplies single-phase electric power from an electrical grid to remote areas at lowest cost. The earth is used as the return path for the current, to avoid the need for a second wire to act as a return path.
A telluric current, or Earth current, is an electric current that flows underground or through the sea, resulting from natural and human-induced causes. These currents have extremely low frequency and traverse large areas near or at the Earth's surface. The Earth's crust and mantle are host to telluric currents, with around 32 mechanisms generating them, primarily geomagnetically induced currents caused by changes in the Earth's magnetic field due to solar wind interactions with the magnetosphere or solar radiation's effects on the ionosphere. These currents exhibit diurnal patterns, flowing towards the Sun during the day and towards the poles at night.
Atmospheric electricity describes the electrical charges in the Earth's atmosphere. The movement of charge between the Earth's surface, the atmosphere, and the ionosphere is known as the global atmospheric electrical circuit. Atmospheric electricity is an interdisciplinary topic with a long history, involving concepts from electrostatics, atmospheric physics, meteorology and Earth science.
This is an alphabetical list of articles pertaining specifically to electrical and electronics engineering. For a thematic list, please see List of electrical engineering topics. For a broad overview of engineering, see List of engineering topics. For biographies, see List of engineers.
Galvanic isolation is a principle of isolating functional sections of electrical systems to prevent current flow; no direct conduction path is permitted.
The Carrington Event was the most intense geomagnetic storm in recorded history, peaking from 1–2 September 1859 during solar cycle 10. It created strong auroral displays that were reported globally and caused sparking and even fires in multiple telegraph stations. The geomagnetic storm was most likely the result of a coronal mass ejection (CME) from the Sun colliding with Earth's magnetosphere.
The March 1989 geomagnetic storm occurred as part of severe to extreme solar storms during early to mid March 1989, the most notable being a geomagnetic storm that struck Earth on March 13. This geomagnetic storm caused a nine-hour outage of Hydro-Québec's electricity transmission system. The onset time was exceptionally rapid. Other historically significant solar storms occurred later in 1989, during a very active period of solar cycle 22.
Solar cycle 22 was the 22nd solar cycle since 1755, when extensive recording of solar sunspot activity began. The solar cycle lasted 9.9 years, beginning in September 1986 and ending in August 1996. The maximum smoothed sunspot number observed during the solar cycle was 212.5, and the starting minimum was 13.5. During the minimum transit from solar cycle 22 to 23, there were a total of 309 days with no sunspots.
The impact of the solar wind onto the magnetosphere generates an electric field within the inner magnetosphere - the convection field-. Its general direction is from dawn to dusk. The co-rotating thermal plasma within the inner magnetosphere drifts orthogonal to that field and to the geomagnetic field Bo. The generation process is not yet completely understood. One possibility is viscous interaction between solar wind and the boundary layer of the magnetosphere (magnetopause). Another process may be magnetic reconnection. Finally, a hydromagnetic dynamo process in the polar regions of the inner magnetosphere may be possible. Direct measurements via satellites have given a fairly good picture of the structure of that field. A number of models of that field exists.
Solar phenomena are natural phenomena which occur within the atmosphere of the Sun. They take many forms, including solar wind, radio wave flux, solar flares, coronal mass ejections, coronal heating and sunspots.
This glossary of electrical and electronics engineering is a list of definitions of terms and concepts related specifically to electrical engineering and electronics engineering. For terms related to engineering in general, see Glossary of engineering.
The solar storms of August 1972 were a historically powerful series of solar storms with intense to extreme solar flare, solar particle event, and geomagnetic storm components in early August 1972, during solar cycle 20. The storm caused widespread electric‐ and communication‐grid disturbances through large portions of North America as well as satellite disruptions. On 4 August 1972 the storm caused the accidental detonation of numerous U.S. naval mines near Haiphong, North Vietnam. The coronal mass ejection (CME)'s transit time from the Sun to the Earth is the fastest ever recorded.
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