The vacuum interrupter, also known as the vacuum switch tube or vacuum bubble, is the core component of the vacuum switch. Its core function is to utilize the excellent insulation and arc extinguishing characteristics of the vacuum. It realizes the closing and opening operations of the circuit through a pair of electrodes (contacts) and other components sealed in a vacuum. After the power is cut off, the device can quickly extinguish the arc and effectively suppress the current, thereby ensuring the safe and stable operation of the power system.
Vacuum interrupters can be classified according to different standards. According to the shell material, they can be divided into glass vacuum interrupters and ceramic vacuum interrupters. According to the purpose, vacuum interrupters are divided into vacuum interrupters for circuit breakers, load switches, contactors, reclosers, sectionalizers, and other special purposes.
Basic structure of vacuum interrupter
The core components of the vacuum interrupter include the airtight insulation system, which ensures the insulation performance of the equipment in a vacuum state; the conductive system, which is responsible for the closing and opening operations of the circuit; the shielding system, which is used to protect the contacts from external interference; and the contact system, which is a key component for current transmission. These components together constitute the basic structure of the vacuum interrupter, ensuring its efficient and safe operation.
The airtight insulation system is mainly composed of an insulating shell made of glass or ceramic, a moving end cover, a fixed end cover, and a stainless steel bellows. Among them, the insulating shell is the core component of the system, which not only plays a supporting role, but also is the key guarantee of airtightness. The bellows, as a guide and sealing component for the movement of the moving electrode, has extremely high mechanical life requirements to ensure the stable operation of the vacuum interrupter.
The conductive system of the arc extinguishing chamber is composed of multiple components such as a fixed conductive rod, a fixed arc surface, a fixed contact, a moving contact, a moving arc surface, and a moving conductive rod. Among them, the fixed conductive rod, the fixed arc surface, and the fixed contact are collectively referred to as the fixed electrode, while the moving contact, the moving arc surface, and the moving conductive rod are collectively referred to as the moving electrode. This design enables the operating mechanism to easily achieve the closure of the two contacts through the movement of the moving conductive rod, thereby completing the circuit connection.
In order to ensure that the contact resistance between the two contacts remains minimal and stable, and to enhance the mechanical strength of the arc extinguishing chamber when it is subjected to dynamic and stable current, the vacuum switch is specially equipped with a guide sleeve at one end of the moving conductive rod, and supplemented by a set of compression springs, so that the two contacts always maintain a constant rated pressure. When the vacuum switch breaks the current, the two contacts of the arc extinguishing chamber will separate and generate an arc until the arc extinguishes itself when the current naturally passes zero, thereby completing the circuit breaking.
In addition, the moving and static conductive rods of the vacuum arc extinguishing chamber are refined with oxygen-free copper. As the main conductive circuit, they undertake the important task of conducting current. The guide sleeve is usually refined with insulating materials. Its core function is to ensure that the moving conductive rod can make smooth linear motion along the axis of the vacuum arc extinguishing chamber during the opening and closing process. At the same time, it can also effectively prevent the current of the conductive circuit from being shunted to the bellows, thereby extending the service life of the vacuum arc extinguishing chamber.
The shielding system is mainly composed of a shielding tube, a shielding cover and other related parts. Among them, the shielding tube is the core component of the system, and its material can be selected from a variety of materials such as oxygen-free copper, stainless steel, electrical pure iron or copper-chromium alloy. The main functions of the system include:
- Reduce the pollution of the inner wall of the insulating shell by metal vapor and droplets generated by the contacts during the arcing process, thereby preventing the reduction of the insulation strength of the vacuum interrupter shell or the occurrence of flashover.
- Optimize the electric field distribution inside the vacuum interrupter and promote the miniaturization of the insulating shell of the vacuum interrupter, especially in the miniaturization of vacuum interrupters with high voltage levels.
- Condensation of arc products. Especially when the vacuum interrupter breaks the short-circuit current, the shielding system can absorb most of the heat energy generated by the arc, thereby enhancing the dielectric recovery strength between the contacts. The more arc products the shielding tube condenses, the greater the energy it absorbs, and the more conducive it is to improving the breaking capacity of the vacuum interrupter.
Contact system
As the core component of the vacuum switch, the key to the performance of the vacuum interrupter lies in the contact system. The contact system plays a vital role in the opening and closing process of the circuit.
●Contact structure
When the vacuum interrupter breaks the short-circuit current, the contact structure plays a vital role. It effectively limits the formation of anode spots on the contact surface by forming a transverse or longitudinal magnetic field, thereby improving the breaking capacity of the interrupter. The contact structure generates the required magnetic field by changing the direction of the current and by using magnetic materials to gather the magnetic lines of force.
The contact structure of the vacuum interrupter is diverse, including cylindrical contacts, transverse magnetic field contacts such as spiral groove transverse magnetic, cup transverse magnetic and swastika groove transverse magnetic, and longitudinal magnetic field contacts such as open oblique groove longitudinal magnetic, coil longitudinal magnetic and horseshoe longitudinal magnetic. In addition, there are R-type contacts, whose contact structure and contact are integrated, and the magnetic field direction is alternating longitudinal magnetic.
●Contact material
The contact is the key part of conducting arc and extinguishing arc, so the requirements for materials are extremely strict. At present, the contact materials of the vacuum interrupter for circuit breakers are mainly copper-bismuth alloy, copper-chromium alloy and copper-tungsten alloy. Among them, copper-chromium alloy is widely used due to its excellent performance. A copper-chromium alloy sheet with a thickness of 3mm is welded on the butt surface of the upper and lower contacts. The rest can be made of oxygen-free copper.
● Transverse and longitudinal magnetic field contacts and their functions
When the transverse magnetic field contact breaks the short-circuit current in the vacuum interrupter, a magnetic field perpendicular to the electrode axis is generated. This magnetic field makes the vacuum arc move at high speed along the contact surface, avoiding serious melting of the contact surface, and quickly restores the insulation strength after the current passes zero, which is conducive to the extinction of the arc.
The longitudinal magnetic field contact generates a magnetic field consistent with the direction of the electrode axis. This magnetic field can increase the conversion current value from the diffuse arc to the contraction arc. Under the action of a sufficiently strong longitudinal magnetic field, the arc spots are evenly distributed on the surface of the electrode contact, avoiding local serious melting of the contact surface, and at the same time have the advantages of low arc voltage and small arc energy, which is very beneficial to the recovery of insulation strength after the arc and the improvement of breaking capacity.
At present, in the field of vacuum interrupters, large-capacity products generally adopt the longitudinal magnetic field contact design. This is mainly due to the excellent performance of the longitudinal magnetic field contact, including its low electrical wear, long durability and strong breaking capacity.