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Related knowledge about vacuum circuit breaker

2022-08-15

2021-11-09

Features:
"Vacuum circuit breaker" is named after its arc extinguishing medium and the insulating medium of the contact gap after arc extinguishing are both high vacuum; it has the advantages of small size, light weight, suitable for frequent operation, and no need for maintenance of arc extinguishing. The application in the power grid is more popular. The vacuum circuit breaker is an indoor power distribution device in a 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. For maintenance and frequent operation places, circuit breakers can be configured in middle cabinets, double-layer cabinets, and fixed cabinets to control and protect high-voltage electrical equipment.

Specification:
1. Vacuum circuit breakers can usually be divided into multiple voltage levels. The low-voltage type is generally used for explosion-proof electrical applications. Like coal mines and so on.
2. The rated current reaches 5000A, and the breaking current reaches a good level of 50kA, and has developed to a voltage of 35kV.

Main domestic standards
JB/T 3855-2008 "High Voltage AC Vacuum Circuit Breaker"
DL/T 403-2017 "High Voltage AC Vacuum Circuit Breaker"
It needs to be explained here: There is no special standard corresponding to China's JB 3855 in the IEC standard, but "IEC56 AC high-voltage circuit breaker" is applied. Therefore, China's vacuum circuit breaker standards are higher or stricter than IEC standards in at least the following aspects:

(1) Insulation level:

Description Test voltage IEC China
1min power frequency withstand voltage (kV) 42 42 (between poles, pole to ground) 48 (between fractures)
1.2/50 Impulse withstand voltage (kV) 75 75 (between poles, pole to ground) 84 (between fractures)

(2) The withstand voltage level of the vacuum interrupter fracture after the end of the electrical life test: there is no regulation in IEC56.
China's JB3855-96 stipulates that the insulation capacity of the vacuum circuit breaker after completing the electrical life test should not be less than 80% of the initial insulation level, that is, the power frequency is 1min 33.6kV and the impact is 60kV.
(3) Contact bounce time: IEC has no regulations, but China's regulations require no more than 2ms.
(4) Test current for temperature rise test: In the IEC standard, the test current is equal to the rated current of the product. China DL403-91 stipulates that the test current is 110% of the rated current of the product.

The main structure
Vacuum circuit breakers mainly include three parts: vacuum interrupter, electromagnetic or spring operating mechanism, bracket and other components.

Vacuum interrupter
According to different switch types, there are outer shielded ceramic vacuum interrupter, middle sealed cup-shaped longitudinal magnetic field miniaturized vacuum interrupter, and inner sealed glass bubble interrupter. The basic structure is as follows:

① Airtight insulation system (housing)
The airtight insulation system composed of ceramic, glass or glass-ceramics airtight insulation cylinder, moving end cover plate, fixed end cover plate and stainless steel bellows is a vacuum airtight container. In order to ensure air tightness, in addition to strict operation techniques in the sealing type, the material itself is also required to have a small air permeability and internal outgassing.

② Conductive system
It is composed of a fixed conductive rod, a fixed arc surface, a fixed contact, a movable contact, a movable arc surface, and a movable conductive rod. There are roughly three types of contact structures: cylindrical contact, transverse magnetic field contact with spiral groove arc surface, and longitudinal magnetic field contact. At present, using longitudinal magnetic field technology, this kind of arc extinguishing chamber has strong and stable arc breaking ability.

③ Shielding system
The shielding cover is an indispensable element in the vacuum interrupter, and there are many kinds of main shielding covers surrounding the contacts, bellows shielding covers, and pressure equalizing shielding covers. The function of the main shielding cover is to:
a) prevent the arc product from splashing to the inner wall of the insulating shell during the arcing process, thereby reducing the insulation strength of the shell.
b) Improve the uniformity of the electric field distribution inside the arc extinguishing chamber, which is beneficial to reduce the local field strength and promote the miniaturization of the vacuum interrupter.
c) Condensing the arc product, absorbing part of the arc energy, and helping to restore the strength of the gap after the arc.

Operating mechanism
According to different types of circuit breakers, different operating mechanisms are used. Commonly used operating mechanisms are:
    1) spring operating mechanism,
    2) CD10 electromagnetic operating mechanism,
    3) CD17 electromagnetic operating mechanism,
    4) CT19 spring energy storage operating mechanism,
    5) CT8 spring energy storage operating mechanism.

Other parts
Base, insulating support, insulator, etc.

Features
①The contact distance is small, the contact distance of 10KV vacuum circuit breaker is only about 10mm, the operating power of the operating mechanism is small, the stroke of the mechanical part is small, and the mechanical life is long.
②The arcing time is short and has nothing to do with the magnitude of the switching current, generally only half a cycle.
③After the arc is extinguished, the recovery speed of the contact gap medium is fast, and the performance of the near-breaking fault is better.
④Since the wear of the contact is small when breaking current, the electrical life of the contact is long, with full capacity breaking up to 30-50 times, rated current breaking up to more than 5000 times, low noise and suitable for frequent operation.
⑤Small size and light weight.
⑥Suitable for breaking capacitive load current.
Because of its many advantages, it is widely used in substations. The current models mainly include: ZN12-10, ZN28A-10, ZN65A-12, ZN12A-12, VS1, ZN30, ZW32, ZW43 etc.

Working principle
The working principle of the vacuum circuit breaker is: when the moving and static contacts are opened under the action of the operating mechanism, an arc is generated between the contacts, and the contact surface volatilizes steam at high temperature. Because the contact is designed with a special shape, When passing through, a magnetic field is generated. Under the action of this magnetic field, the arc moves rapidly along the tangential direction of the contact surface. Part of the metal vapor is condensed on the metal cylinder (shielding cover). The strength of the medium quickly recovered.

Well, I introduce it here today, and you can learn more about the specific products on the product page.