Vacuum interrupter is an electric vacuum device that uses high vacuum working insulating arc extinguishing medium and realizes the on-off function of power circuit by a pair of contacts sealed in vacuum. When it disconnects a certain amount of current, at the moment of separation of the dynamic and static contacts, the current shrinks to the point where the contacts just separate, resulting in a sharp increase in resistance between electrodes and a rapid increase in temperature, until the evaporation of electrode metal occurs, and at the same time, a very high electric field intensity is formed, resulting in extremely strong emission and gap breakdown, resulting in vacuum arc. When the power frequency voltage is close to zero, and at the same time, due to the increase of contact opening distance, The plasma of the vacuum arc quickly diffuses around.
A vacuum interrupter generally has one fixed and one moving contact, a flexible bellows to allow movement of that contact, and arc shields enclosed in a hermetically-sealed glass, ceramic or metal housing with a high vacuum. The moving contact is connected by a flexible braid to the external circuit, and is moved by a mechanism when the device is required to open or close. Since air pressure tends to close the contacts, the operating mechanism must hold the contacts open against the closing force of air pressure on the bellows.
The vacuum interrupter bellows allows the moving contact to be operated from outside the interrupter enclosure, and must maintain a long-term high vacuum over the expected operating life of the interrupter. The bellows is made of stainless steel with a thickness of 0.1 to 0.2 mm. Its fatigue life is affected by heat conducted from the arc.
To enable them to meet the requirements for high endurance in real practice, the bellows are regularly subjected to an endurance test every three months. The test is carried out in a fully automatic test cabin with the travels adjusted to the respective type.