Vacuum interrupter

In electrical engineering, a vacuum interrupter is a switch which uses electrical contacts in a vacuum. It is the core component of medium-voltage circuit-breakers, generator circuit-breakers, and high-voltage circuit-breakers. Separation of the electrical contacts results in a metal vapour arc, which is quickly extinguished. Vacuum interrupters are widely used in utility power transmission systems, power generation unit, and power-distribution systems for railways, arc furnace applications, and industrial plants. Since the arc is contained within the interrupter, switchgear using vacuum interrupters are very compact compared with switchgear using air, SF6 or oil as arc-suppression medium. Vacuum interrupters can be used for circuit-breakers and load switches. Circuit-breaker vacuum interrupters are used primarily in the power sector in substation and power-generation facilities, and load-switching vacuum interrupters are used for power-grid end users. The use of a vacuum for switching electrical currents was motivated by the observation that a one-centimeter gap in an X-ray tube could withstand tens of thousands of volts. Although some vacuum switching devices were patented during the 19th century, they were not commercially available. In 1926, a group led by Royal Sorensen at the California Institute of Technology investigated vacuum switching and tested several devices; fundamental aspects of arc interruption in a vacuum were investigated. Sorenson presented the results at an AIEE meeting that year, and predicted the switches' commercial use. In 1927, General Electric purchased the patent rights and began commercial development. The Great Depression and the development of oil-filled switchgear caused the company to reduce development work, and little commercially important work was done on vacuum power switchgear until the 1950s. In 1956, H. Cross revolutionized the high-frequency-circuit vacuum switch and produced a vacuum switch with a rating of 15 kV at 200 A. Five years later, Thomas H.