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Background
The sun continually emits ions and subatomic particles into space̵2;the solar wind. Occasionally it discharges much larger amounts of matter̵2;called coronal mass ejections̵2;mostly ionized hydrogen and helium. These coronal mass ejections, measuring up to a million degrees Celsius at the sun̵7;s surface, approach the earth at about 450 kilometers per second. The ejections̵7; large amount of matter and great speed interact with the earth̵7;s magnetic sphere and can cause disruptions in communications, electrical power and satellite operations. The tendency to send electricity over long transmission lines makes these systems especially vulnerable to geomagnetic disturbances or storms. Other factors that increase the vulnerability of technological systems to geomagnetic storms include their proximity to the polar auroral zone, locations in coastal areas, transmission line orientation and length, DC resistance of conductor components, connections modes and station grounding methods.
Problems Caused by the Solar Wind
In power systems especially, geomagnetic storms induce strong currents within transformers. These currents overpower the systems̵7; filters and compensators and disrupt transformer function. First noted in 1940, these disruptions caused major power disturbances in 1957, 1958, 1968, 1970, 1972, 1974, 1979, 1982, 1983 and 1989. In 1989, geomagnetically induced currents̵2;or GICs̵2;destroyed a transformer associated with a nuclear power plant. The currents also increase harmonics in sensitive digital relays, creating false trips in equipment which in turn shut down electrical systems. Other problems caused by solar disturbances include unusual transformer noise and heating, power swings, frequency excursions, harmonic currents, voltage fluctuations, failure of protective relays and neutral ground currents tripping capacitor banks.
Minimizing Solar Wind Impacts
Utility companies and other technology-based operations can minimize the impacts from geomagnetic storms. They should study their systems for vulnerabilities to GIC effects and evaluate the risks of harmonic resonances and voltage collapses from transformer failures. As their budgets allow, they should replace all transformers with more GIC-immune models, such as those with three-phase, three-leg core designs, and redesign their systems to tolerate large voltage swings. Other preventive measures include hardening buildings and systems, providing backup communication alternatives for system operators, separating interconnected systems into several non-synchronous islands, balancing loads between transmission lines and improving and exercising recovery capabilities. Companies should also access the daily and three-hourly indexes of solar activity provided by the National Oceanic and Atmospheric Administration̵7;s Space Weather Prediction Center, designate an employee to report any watches, alerts and warnings from the Center and establish procedures to respond to these alerts.