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Composition Principle and Application of Vacuum Switch Tube (Vacuum Arc Extinguishing Chamber)
EECTECH Vacuum switch tube (vacuum interrupter)
Vacuum switch tube (vacuum interrupter)
Vacuum switch tube, also known as vacuum arc extinguishing chamber, is the core component of medium and high voltage power switch. Its main function is to quickly extinguish the arc and suppress the current after cutting off the power supply of medium and high voltage circuit through the excellent insulation of vacuum in the tube, so as to avoid accidents and accidents. It is mainly used in power transmission and distribution control system, and also applied in metallurgy, mining, petroleum, chemical industry, railway and broadly. Distribution systems such as broadcasting, communication, industrial high frequency heating, etc. It has the characteristics of energy saving, material saving, fire prevention, explosion proof, small size, long life, low maintenance cost, reliable operation and pollution-free. The vacuum interrupter can be divided into circuit breaker interrupter and load switch interrupter. The circuit breaker interrupter is mainly used in substations and power network facilities in power departments, and the load switch interrupter is mainly used for end users of power grid.
structural style
It mainly consists of air-tight insulation shell, conductive circuit, shielding system, bellows and other parts.
1. Air-tight insulation system
The air-tight insulation system consists of an air-tight insulation shell made of glass or ceramic, a movable end cover plate, a fixed end cover plate and a stainless steel bellows. In order to ensure good air tightness between glass, ceramics and metal, in addition to strict operation technology, the material itself is required to be as small as possible and the internal air release is limited to a minimum. The function of stainless steel bellows can not only isolate the vacuum state inside the vacuum interrupter from the atmospheric state outside, but also make the movable contacts and the movable conductive rods move in a specified range to complete the closing and breaking operation of the vacuum switch.
2. Conductive system
The conductive system of the arc extinguishing chamber consists of a fixed conductive rod, a fixed arc surface, a fixed contact, a moving contact, a running arc surface and a moving conductive rod. Among them, the fixed conductive rod, the fixed arc surface and the fixed contact are called the fixed electrode, the movable contact, the moving arc surface and the movable conductive rod are called the movable electrode. When the vacuum circuit breaker, the vacuum load switch and the vacuum contactor are closed, the operating mechanism closes the two contacts through the movement of the movable conductive rod and completes the circuit connection. In order to reduce the contact resistance between two contacts as much as possible and maintain stability and have good mechanical strength when the arc extinguishing chamber withstands dynamic stable current, a guide sleeve is arranged at one end of the dynamic conductive rod of the vacuum switch, and a set of compression springs are used to maintain a rated pressure between the two contacts. When the vacuum switch breaks off the current, the two contacts of the interrupter are separated and the arc is generated between them until the arc is extinguished when the current naturally passes zero.
3. Shielding System
The shielding system of vacuum interrupter is mainly composed of shielding barrel, shielding cover and other parts.
The main functions of the shielding system are:
(1) Prevent the contact from splashing a large amount of metal vapor and droplets during arc ignition, pollute the inner wall of the insulation case, and avoid the decrease of insulation strength or flashover of the vacuum interrupter case.
(2) Improving the electric field distribution inside the vacuum interrupter is beneficial to the miniaturization of the insulation shell of the vacuum interrupter, especially for the miniaturization of the high voltage vacuum interrupter.
(3) Absorbing part of arc energy and condensing arc products. Especially when short circuit current is interrupted in vacuum interrupter, most of the heat energy generated by arc is absorbed by shielding system, which is conducive to improving the dielectric recovery strength between contacts. The larger the amount of arc products absorbed by the shielding system, the greater the energy absorbed by the shielding system, which plays a good role in increasing the interruption capacity of the vacuum interrupter.
4. Contacts
Contacts are the places where arcs are generated and extinguished, which require high materials and structures.
4.1 The requirements for contact materials are as follows:
(1) High interruption capability. The material itself is required to have high conductivity, low thermal conductivity, large thermal capacity and low thermal electron emission capability.
(2) High breakdown voltage. If the breakdown voltage is high, the dielectric recovery strength will be high, which is beneficial to arc extinguishing.
(3) High resistance to electric corrosion. That is to say, it can withstand the ablation of arc and has less metal evaporation.
(4) Anti-welding ability.
(5) Low cut-off current, expected to be less than 2.5A.
(6) Low gas content. Low gas content is the requirement of all materials used in vacuum interrupter. Especially for copper, oxygen-free copper must be treated by special process with low gas content. The solder is made of silver and copper alloys.
At present, most contact materials of vacuum interrupter for circuit breaker are copper-chromium alloy, with copper and chromium accounting for 50% respectively. A copper-chromium alloy sheet is welded on the butt surfaces of the upper and lower contacts with a thickness of 3 mm. The rest is called contact base, which can be made of oxygen-free copper.
4.2 Contact Structure
The contact structure has a great influence on the interruption ability of the isolation chamber. The arc-extinguishing effect of different structure contacts is different. In the early stage, simple cylindrical contacts were used. Although the structure was simple, the breaking ability could not meet the requirements of circuit breakers. Only the current below 10 kA could be interrupted. At present, only vacuum switches such as vacuum load switches and high-voltage vacuum contactors were used. At present, three kinds of contacts are commonly used: spiral groove type contacts, cup type contacts with inclined grooves and cup type contacts with longitudinal magnetic field. Among them, cup type contacts with longitudinal magnetic field are mainly used.
5. Bellows
The bellows of vacuum interrupters are mainly responsible for ensuring the movement of moving electrodes within a certain range and keeping high vacuum for a long time, as well as ensuring the vacuum interrupters.