[Research on the old refining process of miniaturized vacuum interrupter]: Abstract: This paper focuses on the old refining process of miniaturized vacuum interrupter according to the experience in the research and development and production practice of miniaturized vacuum interrupter. 1 Overview After nearly thirty years of development, vacuum switch technology has increased its market share year by year, and there are more and more manufacturers, and the market competition is very fierce. ...
Abstract: This paper focuses on the old refining process of miniaturized vacuum interrupter according to the experience in the research and development and production practice of miniaturized vacuum interrupter.
1 Overview
After nearly 30 years of development, vacuum switch technology has increased its market share year by year, and there are more and more manufacturers, and the market competition is very fierce. Especially since joining the WTO, foreign vacuum switch manufacturing industries have entered the Chinese market in the form of sole proprietorship and joint venture, making the competition more intense. The market demand for advanced miniaturized vacuum switches is becoming more and more urgent, and users need products with small dimensions, small footprint, low cost and superior performance. Therefore, in recent years, countries around the world, especially Japan, the United States and other countries with a high level of scientific and technological development, have been committed to the research of vacuum interrupter miniaturization, and have made breakthroughs.
In order to realize the miniaturization of vacuum interrupter, the technical researchers of Jinzhou Huaguang Power Electronics (Group) Company have conducted in-depth research on vacuum arc, electric vacuum materials, distribution of electric field strength and production methods inside the interrupter, and the design level and manufacturing process of vacuum interrupter have been continuously improved and perfected, and a new generation of U series miniaturized vacuum interrupter has been launched.
U series miniaturized vacuum interrupter has changed the previous design mode and process mode, adopted a new design concept in the design of the internal structure of the product, and made a great breakthrough in the manufacturing process, and its product features are as follows:
(1) The new longitudinal magnetic uniform contact structure developed by itself is adopted. This contact structure generates a stronger and more uniform longitudinal magnetic field in the contact gap during arc ignition than the current common longitudinal magnetic contact structure. Under the action of strong magnetic field, the arc is effectively controlled to burn in a larger area, expand the effective utilization area of the contact, improve the current density distribution on the surface of the contact, and keep the arc always diffusion type, thereby reducing the arc voltage and arc energy, greatly improving the breaking ability, and increasing the breaking capacity by more than 15% compared with the original cup-shaped contact structure.
(2) Through computer-aided design, the uniformity of the electric field intensity distribution inside the arc extinguishing chamber is improved, the internal structure of the arc extinguishing chamber is optimized, and the insulation level inside the arc extinguishing chamber is improved, so as to realize the miniaturization of the arc extinguishing chamber, and its volume is only 50%~70% of the original structure.
(3) The new "one-time sealing and discharging" process is adopted to complete the one-time sealing and discharging of the arc extinguishing chamber from the components to the whole pipe, which reduces the secondary pollution of the components by people and the environment, improves the vacuum degree and cleanliness inside the arc extinguishing chamber, and improves the breaking performance, insulation level and coaxial level of the arc extinguishing chamber. At the same time, the new process structure reduces the sealing weld of the arc extinguishing chamber, from the original 9 welds to 6 welds, the probability of air leakage of the arc extinguishing chamber is greatly reduced, and the reliability of the seal is increased by 33%.
(4) The new type of bellows anti-torsion structure is adopted, which not only prevents the bellows from being sprained and leaks, but also makes the appearance of the whole pipe more beautiful, and also brings convenience to the installation.
Jinzhou Huaguang Power Electronics (Group) Co., Ltd. has developed a 12kV grade of 20kA, 25kA, 31.5kA, 40kA, 80kA for circuit breakers and 40.5kV grades of 25kA, 31.5kA and 20kA for load switch U series miniaturized vacuum interrupter, which is a replacement product developed by the company and has independent intellectual property rights.
The superior performance and miniaturized volume of the U series vacuum interrupter and the application of composite insulation not only reduce the phase spacing and reduce the overall size of the vacuum circuit breaker, but also can meet the larger breaking capacity and higher post-arc insulation level. In addition, after using a miniaturized vacuum interrupter for the current switch, the additional insulation between phases can also be removed, which can not only reduce costs, but also facilitate installation and debugging.
The superior breaking performance and high post-arc insulation level of the U series miniaturized vacuum interrupter are due to the advanced design method and the adoption of the new "primary sealing and discharge" process, which is also inseparable from the improvement of the old refining process. The old refining process of vacuum interrupter is divided into current old refining and voltage old refining, and this paper focuses on the old refining process of miniaturized vacuum interrupter according to the experience in the research and development and production practice of miniaturized vacuum interrupter.
2 High current old refining
High-current old refining is that the vacuum arc extinguishing chamber pulls the contact at the same time with a large current of hundreds of amperes, so that a diffusion arc is generated between the contacts, and the burning arc peels off the dirt, oxides and gases covered with the surface of the contact, so that the surface of the contact becomes a completely fresh active surface, which plays a role in purifying the surface of the contact. Therefore, it can be said that compared with the old current refining and the voltage refining, it has the effect of complete degassing.
Jinzhou Huaguang Power Electronics (Group) Company adopts the DC old refining method, takes the DC voltage of about 100V, adjusts the arc current to 100 amperes to hundreds of amps, and divides the contact 10~20 times. Each time the arc is combined, the arc has a long enough arc burning time, and after accumulating a certain time, the purpose of purifying and degassing the surface of the contact can be achieved. The ablative effect of current aging on the contact surface mainly comes from the bombardment of positive ions on the cathode, which has a good ablative effect on the cathode surface [1], in order to perform aging on the other contact, it is necessary to change the polarity of the DC power supply and repeat the last operation. The performance of the breaking short-circuit current and opening and closing capacitor bank of the vacuum interrupter chamber after high-current aging is more stable than that of the arc extinguishing chamber without current aging [2], mainly because the purification of the surface of the contact and the gas absorbed by the surface layer are removed, and the arc combustion contact releases less gas during the breaking, and the recovery of the medium strength between the contacts is very powerful.
U series miniaturized vacuum interrupter adopts a new longitudinal magnetic uniform contact structure, this contact structure during arc ignition, in the contact gap to produce a stronger and more uniform longitudinal magnetic field than the current general longitudinal magnetic contact structure, the arc is effectively controlled in a larger area of combustion, expanding the effective utilization area of the contact, under the same current level, the contact surface area is reduced by more than 20%. In order to avoid the specification of high-current aging is too heavy, the surface of the contact is seriously burned, affecting the insulation level, especially affecting the impact withstand voltage level, U series miniaturized products high-current aging test, arc current adjusted to 80~100 amps, combined contact positive and negative polarity 5~10 times, the specific number of times according to the arc, arc color from white or red to light blue-green is appropriate.
3. Ultra-high pressure old refining
The high-voltage aging effect is one of the main factors determining the breakdown characteristics of insulation in vacuum, and it has become a topic to achieve high voltage and miniaturization. There are four commonly used high-pressure old refining methods: glow discharge old refining method, inflatable old refining method, current old refining method, and spark old refining method. For the sealed vacuum interrupter, the spark old refining method is the only practical way to improve the pressure resistance level of the vacuum interrupter [3], and the spark old refining method is also the power frequency old refining method. Jinzhou Huaguang Power Electronics (Group) Company adopts ultra-high voltage power frequency old refining, which is characterized by:
(1) The arc extinguishing chamber is immersed in an insulating medium, and the old refining voltage is increased by about 1.5 times compared to the air, making the internal smelting of the vacuum arc extinguishing chamber more thorough;
(2) The boost of ultra-high voltage power frequency old refining has protective measures, once the breakdown current is large and threatens the safety of the product, it will automatically reduce the voltage to protect the arc extinguishing chamber from damage;
(3) Under static conditions, the vacuum arc extinguishing chamber is subjected to high voltage, causing strong spark discharge between contacts and between contacts and shielding covers. The vacuum interrupter uses this method to eliminate the high β emission point on the surface of the contact and shielding case, improve the surface condition of the contact and shielding case, and improve its breakdown voltage and stability under long-term operation.
After the miniaturization of the vacuum interrupter, the volume of the interrupter becomes smaller and smaller, so the old refining process also needs to be reexplored to determine the old refining process that is more suitable for the mass production of miniaturized products. Here we focus on the exploration process of high-voltage old refining process of miniaturized vacuum interrupter, including the protection of external insulation, the opening distance of old refining, the boost speed of old refining, the determination of the voltage value of old refining and the determination of voltage stability time.
3.1 External insulation protection
One of the key technologies to solve the vacuum interrupter withstand high voltage and strong electric field is the improvement of insulation along the surface, especially after the vacuum interrupter is miniaturized to the greatest extent, the external insulation of the vacuum interrupter itself (mainly refers to the external insulation of the vacuum interrupter for composite insulation) can no longer meet the higher old refining voltage and normal insulation requirements
