Vacuum interrupter is the core components of the high-voltage switches, its main role is through the tube vacuum excellent insulation to quickly extinguish the arc and suppress the current when the medium/high voltage circuit was cut off, to avoid accidents, mainly used in power transmission control system, but also used in metallurgy, mining, petroleum, chemical, railway, radio, communications, industrial high-frequency heating and other power distribution systems. With energy saving, fire-proof, explosion-proof, small size, long life, low maintenance costs, reliable operation and non-polluting and so on. Vacuum interrupter could use for circuit breaker and load switch, circuit breaker’s vacuum interrupter is mainly used in the power sector in the substation and power grid facilities, load switch’s vacuum interrupter is mainly used for power grid Of the end user.

Classification

According to the shell: glass vacuum interrupter, ceramic vacuum interrupter.
According to the usage: Vacuum interrupter for circuit breakers, vacuum interrupter for load switch, vacuum interrupter for contactor, vacuum interrupter for recloser, vacuum interrupter for splitter and other special purpose vacuum interrupter.
According to the type: VG, VS, HCJ3, WL, HCJ5, VN, CE, VX different type vacuum interrupter for vacuum contactor and vacuum switches.

Structure type

Mainly by the airtight insulation shell, conductive circuit, shielding system, contacts, bellows and other components of the ceramic shell vacuum interrupter.

Airtight insulation system

Made of glass or ceramic airtight insulation shell, movable flange, fixed flange, stainless steel bellows composed of airtight insulation system. In order to ensure that the good airtight between the glass, ceramic and metal, in addition to sealing when there is a strict operating process, but also requires the material itself as small as the permeability and internal deflation limit to a minimum. The function of the stainless steel bellows not only isolates the vacuum state inside the vacuum interrupter from the external atmosphere, but also moves the movable contact with the conductor within a specified range to complete the closing and breaking of the vacuum switch operating.

Conductive system

Fixed conductor, fixed arcing surface, fixed contact, movable contact, movable arcing surface, the movable conductor constitutes the conductive system of the vacuum interrupter.
Which the fixed conductor, fixed arcing surface and fixed contact called fixed electrode, the movable conductor, movable arcing surface and movable contact called movable electrode, When closing the vacuum circuit breaker, vacuum load switch and vacuum contactor(which is assembled by the vacuum interrupter), the operating mechanism through the movement of the conductor to closed the movable/fixed contacts to complete the circuit connected. In order to make the contact resistance between the two contacts as small as possible and to maintain stability and the vacuum interrupter to withstand the dynamic current with good mechanical strength, the vacuum switch has set the guide sleeve in the side of the conductor, and use a set of compression springs, To make a stable pressure between the two contacts. When the vacuum switch breaking current, the vacuum interrupter’s two contacts separated and generated the arc between in it, until the current crossing zero by nature to extinguished the arc, they completed the circuit breaking.

Shielding system

Vacuum interrupter shielding system mainly by the arcshield, shield cover and other components.
The main role of the shielding system is:
1.To prevent the contacts to produce a large number of metal vapor and droplet splashing during the arcing process, pollution of the inner wall of the insulating shell, to avoid lower the vacuum interrupter shell insulation strength or produce flashover.
2. Improve the electric field inside the vacuum interrupter distribution, is conducive to vacuum interrupter’s insulation shell of the miniaturization, especially has a significant effect for high voltage vacuum interrupter’s miniaturization.
3. Absorb a part of the arc energy, condensation arc resultant. In particular the vacuum interrupter in the breaking short-circuit current, the shielding system is absorbed the most of heat generated by the arc, help to improve the strength of the media between the contacts recovery. The bigger the amount of absorption of the arc resultant, the bigger the energy absorbs, which is good for increasing the breaking capacity of the vacuum interrupter.

Contact system

Contacts is the area which arcing and extinguish the arc, high requirements of the material and structure.
4.1 The following requirements apply to contact materials:
1. High breaking ability. Requirements excellent conductivity of the material, small thermal conductivity, bigger heat capacity, low hot electron emission capability.
2. Requirements High breakdown voltage. Breakdown voltage is high the medium recovery strength is high, favorable for arc suppression.
3. High resistance to electrical corrosion. Can withstand the ablation of the arc, metal evaporation less.
4. Resistance to welding.
5. Low cuf-off current value, hope below 2.5A.
6. Low air content. The low air content is a requirement for all materials used inside the vacuum interrupter. Especially copper, must require low air content of the special process to deal with oxygen-free copper. While the solder is used silver-copper alloy.
Circuit breaker’s vacuum interrupter contact materials are mostly copper-chromium alloy, copper and chromium each 50%. Welding of a copper-chrome alloy sheet on the upper and lower contacts surface , the general thickness of each 3mm. The rest is called a contact seat and can be made of oxygen-free copper.
4.2 contact’s structure
The contact’s structure has a great influence on the breaking capacity of the vacuum interrupter. The different contact’s structure different arc extinguishing performence, early period use of simple cylindrical contact, the structure is simple, but the breaking capacity can not meet the requirements of the circuit breaker, can only break the current below 10ka, and only use on the vacuum load switch and vacuum contactor’s vacuum interrupter only. Usually is Spiral Diameter Structural Contact, With chute cup structure contacts and Longitudinal magnetic field cup structure contact, But mostly use the longitudinal magnetic field cup structure contact.

Bellows

Vacuum interrupter bellows is mainly responsible for ensuring that the moving electrode’s movement in a certain range and keep long-term high vacuum level function, and ensure that the vacuum interrupter has a high mechanical life.
The vacuum interrupter’s bellows is a thin-walled element made of stainless steel with a thickness of 0.1 to 0.2 mm. In the vacuum switche’s open/close process, the vacuum interrupter’s bellows on telescopic effect, the bellows section by the stress effect, so the life of the bellows should be determined by the value of repeated contraction and the working pressure..
The fatigue life of the bellows is related to the heating temperature of the working conditions. After the vacuum interrupter has broken the large short circuit current, the residual heat of the conductor is transferred to the bellows, and the temperature of the bellows is increased. When the temperature rise reaches a certain degree , Which will affect the fatigue strength of bellows.

Working principle

The vacuum interrupter is an electric vacuum device which utilizes the high vacuum working insulating arc extinguished medium to realize the on-off function of the power circuit by a pair of contacts sealed in vacuum environment. When it breaks a certain value of the current, the moving/fixed contact in the separation moment, the current shrink to the contacts just separated point, there is a sharp increase in resistance between the electrodes and the temperature increased rapidly until the occurrence of electrode metal evaporation, while forming xtremely high electric field strength, resulting in a very strong launch and gap breakdown, resulting in vacuum arc, when the power frequency current close to zero, but also the contact’s opening distance increases, the vacuum arc plasma quickly spread to the surrounding, After the arc current is zero, the medium of the contacts gap is rapidly changed from the conductor to the insulator, and the current is broken. Due to the special construction of the contacts, the contact gap will produce a suitable longitudinal magnetic field during the arcing, which allows the arc to be evenly distributed on the contact surface to maintain a low arc voltage, so that the vacuum interrupter has a higher after arc medium strength recovery rate, small arc energy and small corrosion rate. In this way, it improves the ability and life of the vacuum interrupter to break the current.

Production Process

Exhaust plate craft
Refers to the parts of the vacuum interrupter through brazing and argon arc welding process to be made into the exhaust pipe, and then connected to the exhaust plate for vacuum and baking degassing, finally the process of cold folder sealing. This craft, the process is complex, long route, generally 9 processes. So the efficiency is low and the many pollution links of vacuum interrupter parts. Moreover, according to this process to produce vacuum interrupter baking temperature is low (about 450 ℃), and thus degassing is not complete.
Once sealed exhaust craft
It means to brazing the each parts of vacuum interrupter into several parts first, and then several parts assembled into the complete vacuum interrupter, and then complete the exhaust process in the vacuum furnace, bake to the air and brazing sealing process. This craft, the process is simple, there are generally 7 processes, and thus more efficient and less polluting. In addition, according to this process produced vacuum interrupter baking temperature (800 ℃ ~ 900 ℃), and thus exhaust completely.
Completely once sealed exhaust craft
It means to assembled all parts into a complete vacuum interrupter directly, and then one time completion the exhaust, baking, brazing of sealing process in a vacuum furnace. This craft, the process is the most simple, generally only 5 processes, the least man-made links, most stable quality in process, but the requirements of the sealed exhaust equipment is very high.
History of the Vacuum Switches
Humans engaged in the application of vacuum as an extinguishing and insulating medium, and now has a history of more than 100 years. As early as 1893, An American Mr. Rittenhause to design the world’s first vacuum interrupter and published in the form of patents; 1920, Sweden Birka company developed the world’s first Vacuum switch; 1926, the California Institute of Technology Professor Sornsen published a vacuum switch test results, and predicted the application of vacuum switch age will coming soon.
In 1956, H.Cross revolutionized the high frequency circuits vacuum switch produced by Jenning and produced a vacuum switch of 15kv, 200A.
In 1961, the United States General Electric Company first sucessful development the rated voltage 15kv, 12.5ka vacuum circuit breakers basis on previous experience, 1966 successively developed a rated voltage of 15kv, breaking current of 25ka and 31.5ka vacuum circuit breaker , The vacuum switch from the official entry into the ranks of the power switch, the United States therefore become the world’s first mass production and use of vacuum switch country, in its influence and driven, Europe and Asia, some countries have also started the development work, Since then the Vacuum switch get recognition and development from the global.
The 20 century early 70s, With its own huge technical advantages, vacuum switch only took less than 20 years to replace the less oil switch and become the leading product in the medium voltage. At present, single-break vacuum circuit breaker has reached 145kv voltage level, short-circuit breaking current has reached 200ka.

Jucro Electric

Mr. Qiu Min

21/Feb/2017