"Vacuum circuit breaker" is named because its arc extinguishing medium and the insulation medium of contact clearance after arc extinguishing are high vacuum; It has the advantages of small volume, light weight, suitable for frequent operation, arc extinguishing without maintenance, and is widely used in distribution networks. Vacuum circuit breaker is an indoor power distribution device in 3 ~ 10kV, 50Hz three-phase AC system. It can be used as the protection and control of electrical equipment in industrial and mining enterprises, power plants and substations. It is especially suitable for places requiring no oil, less maintenance and frequent operation. Circuit breakers can be configured in central cabinets, double cabinets and fixed cabinets for control and protection of high voltage electrical equipment.
In 1893, Rittenhouse of the United States proposed a simple structure of the vacuum arc extinguishing chamber, and obtained a design patent. The first vacuum switch was made in 1920 by The Swedish Foga Company. Research results published in 1926 also showed the possibility of breaking current in vacuum, but due to the small breaking capacity and the limitation of vacuum technology and vacuum material development, it could not be put into practical use. With the development of vacuum technology, the United States in the 1950s made the first batch of vacuum switches suitable for cutting capacitor banks and other special requirements, the breaking current is still stopped at the level of 4 thousand ampere. Due to the progress of vacuum material smelting technology and the breakthrough of vacuum switch contact structure research, in 1961, the production of 15 kV, breaking current of 12.5 kv vacuum circuit breaker began. In 1966, 15 kv, 26 kv and 31.5 kV vacuum circuit breakers were trial-produced, thus making the vacuum circuit breakers enter the power system of high voltage and large capacity. In the mid 80's, the breaking capacity of vacuum circuit breaker has reached 100 kAMP. Subsequently made of 10 kv, breaking capacity of 1.5 kv three-phase vacuum switch. Since 1970s, China has been able to independently develop and produce vacuum switches of various specifications.
1. Vacuum circuit breakers are usually divided into multiple voltage levels. Low voltage type is generally used for explosion-proof electrical use. Like coal mines and so on.
2. Rated current up to 5000A, breaking current up to a better level of 50kA, and has been developed to the voltage up to 35kV grade.
3. Before the 1980s, vacuum circuit breaker was in the initial stage of development, and the technology was constantly groping. It was not until 1985 that the relevant product standards were made.
Vacuum circuit breaker mainly consists of three parts: vacuum arc extinguishing chamber, electromagnetic or spring operating mechanism, bracket and other parts.
Vacuum arc extinguishing chamber
According to different switch types, there are external shield cover ceramic vacuum arc extinguishing chamber, middle sealing cup-shaped longitudinal magnetic field miniaturization vacuum arc extinguishing chamber, inner sealing glass bubble arc extinguishing chamber, its basic structure is as follows:
Air tight insulation system (shell)
The air-tight insulation system is a vacuum container made of ceramic, glass or glass microcrystalline air-tight insulated cylinder, moving end cover plate, fixed end cover plate and stainless steel bellows. In order to ensure air tightness, in addition to the sealing type to have a strict operation process, but also requires the material itself permeability and small internal ventilation.
It consists of a fixed conductive rod, a fixed running arc surface, a fixed contact head, a moving contact head, a moving running arc surface and a moving conductive rod. There are three kinds of contact structure: cylindrical contact, transverse magnetic contact with spiral groove running arc surface, longitudinal magnetic contact. At present using longitudinal magnetic field technology, this arc extinguishing chamber has strong and stable arc breaking ability.
Shielding cover is an indispensable component in vacuum arc extinguishing chamber, and there are many kinds of shielding cover around contact, bellows shielding and pressure equalizing shielding. The function of the main shielding cover is: a to prevent arc products from splashing into the inner wall of the insulating shell during the arc burning process, thus reducing the insulating strength of the shell. B Improve the uniformity of electric field distribution in the arc extinguishing chamber, which is beneficial to reduce the local field intensity and promote the miniaturization of the vacuum arc extinguishing chamber. C Condenses arc products, absorbs part of arc energy, and contributes to the recovery of the strength of the back-arc clearance medium.
According to the different type of circuit breaker, the operating mechanism is different. Commonly used operating mechanisms are spring operating mechanism, CD10 electromagnetic operating mechanism, CD17 electromagnetic operating mechanism, CT19 spring energy storage operating mechanism, CT8 spring energy storage operating mechanism.
The other part
Base, insulation support, insulator, etc.
(1) The contact opening distance is small, the contact opening distance of 10KV vacuum circuit breaker is only about 10mm, the operation power of the operating mechanism is small, the travel of the mechanical part is small, and the mechanical life is long.
(2) The arc burning time is short, and has nothing to do with the size of the switching current, generally only half cycle.
(3) After extinguishing, the contact clearance medium has fast recovery speed and good fault performance in the near zone of break.
(4) Because the contact wear is small in breaking current, so the electrical life of the contact is long, full capacity breaking up to 30-50 times, rated current breaking up to more than 5000 times, low noise for frequent operation.
(5) Small size, light weight.
(6) Suitable for breaking capacitive load current.
Due to its many advantages, it is widely used in substation, the current models are mainly: ZN12-10, ZN28A-10, ZN65A-12, ZN12A-12, VS1, ZN30 and so on.