Vacuum circuit breakers are circuit breakers that are used to protect medium and high voltage circuits from dangerous electrical situations. Like other types of circuit breakers, they literally break the circuit so that energy cannot continue flowing through it, thereby preventing fires, power surges, and other problems which may emerge. These devices have been used since the 1920s, and several companies have introduced refinements to make them even safer and more effective.
In a vacuum circuit breaker, two electrical contacts are enclosed in a vacuum. One of the contacts is fixed and one is movable. When the circuit breaker detects a dangerous situation, the movable contact pulls away from the fixed contact, interrupting the current. Because the contacts are in a vacuum, arcing between the contacts is suppressed, ensuring that the circuit remains open. As long as the circuit is open, it will not be energized.
Vacuum reclosers will automatically reset when conditions are safe again, closing the circuit and allowing electricity to flow through it. Reclosers can usually go through several cycles before they will need to be manually reset. Some types of vacuum circuit breakers must be reset every time the breaker trips. Before a manual reset, the person doing the resetting needs to check the system to determine what caused the unsafe conditions in the first place, and make sure that they have been addressed.
These circuit breakers are very durable, and they are designed to last for an extended period of time. They can be made with a variety of materials, depending on the need and the preference of the manufacturer. As with other devices used to interrupt current for safety, they're given a rating that indicates the kind of conditions they can handle. When people install circuit breakers, they must confirm that the breaker they are using is suitable for the conditions; a breaker which is rated too low can fail catastrophically.
Other techniques can be used for arc suppression with medium and high voltage electrical systems, such as filling circuit breakers with inert gases to suppress arcing. Arc suppression is a major concern with heavy duty power systems because, if an arc forms, it can override the circuit breaker and create very dangerous conditions. Companies that develop circuit breakers for these applications usually test their designs extensively to confirm that they are safe.