Overview of the development and characteristics of vacuum circuit breaker

[Overview of the development and characteristics of vacuum circuit breaker]: vacuum circuit breaker refers to the circuit breaker whose contacts are closed and opened in vacuum. Vacuum circuit breakers were initially studied by the United Kingdom and the United States, and then developed to Japan, Germany, the former Soviet Union and other countries. China began to study the theory of vacuum circuit breaker from 1959, and formally produced various vacuum circuit breakers in the early 1970s

Vacuum circuit breaker refers to the circuit breaker whose contacts are closed and opened in vacuum.

Vacuum circuit breakers were initially studied by the United Kingdom and the United States, and then developed to Japan, Germany, the former Soviet Union and other countries. China began to study the theory of vacuum circuit breakers in 1959, and formally produced various types of vacuum circuit breakers in the early 1970s. The continuous innovation and improvement of manufacturing technologies such as vacuum interrupter, operating mechanism and insulation level have made the vacuum circuit breaker develop rapidly, and a series of significant achievements have been made in the research of large capacity, miniaturization, intelligence and reliability.

With the advantages of good arc extinguishing characteristics, suitable for frequent operation, long electrical life, high operation reliability, and long maintenance free period, vacuum circuit breakers have been widely used in the urban and rural power grid transformation, chemical industry, metallurgy, railway electrification, mining and other industries in China’s power industry. The products range from several varieties of ZN1-ZN5 in the past to dozens of models and varieties now. The rated current reaches 4000A, the breaking current reaches 5OKA, even 63kA, and the voltage reaches 35kV.

The development and characteristics of vacuum circuit breaker will be seen from several main aspects, including the development of vacuum interrupter, the development of operating mechanism and the development of insulation structure.

Development and characteristics of vacuum interrupters

2.1 Development of vacuum interrupters

The idea of using vacuum medium to extinguish the arc was put forward at the end of the 19th century, and the earliest vacuum interrupter was manufactured in the 1920s. However, due to the limitations of vacuum technology, materials and other technical levels, it was not practical at that time. Since the 1950s, with the development of new technology, many problems in the manufacture of vacuum interrupters have been solved, and the vacuum switch has gradually reached the practical level. In the mid-1950s, General Electric Company of the United States produced a batch of vacuum circuit breakers with rated breaking current of 12KA. Subsequently, in the late 1950s, due to the development of vacuum interrupters with transverse magnetic field contacts, the rated breaking current was raised to 3OKA. After the 1970s, Toshiba Electric Company of Japan successfully developed a vacuum interrupter with longitudinal magnetic field contacts, which further increased the rated breaking current to more than 5OKA. At present, vacuum circuit breakers have been widely used in 1KV and 35kV power distribution systems, and the rated breaking current can reach 5OKA-100KAo. Some countries have also produced 72kV/84kV vacuum interrupters, but the number is small. DC high-voltage generator

In recent years, the production of vacuum circuit breakers in China has also developed rapidly. At present, the technology of domestic vacuum interrupters is on a par with that of foreign products. There are vacuum interrupters using vertical and horizontal magnetic field technology and central ignition contact technology. The contacts made of Cu Cr alloy materials have successfully disconnected 5OKA and 63kAo vacuum interrupters in China, which have reached a higher level. The vacuum circuit breaker can completely use domestic vacuum interrupters.

2.2 Characteristics of vacuum interrupter

The vacuum arc extinguishing chamber is the key component of the vacuum circuit breaker. It is supported and sealed by glass or ceramics. There are dynamic and static contacts and shielding covers inside. There is negative pressure in the chamber. The vacuum degree is 133 × 10 Nine 133 × LOJPa, to ensure its arc extinguishing performance and insulation level when breaking. When the vacuum degree decreases, its breaking performance will be significantly reduced. Therefore, the vacuum arc extinguishing chamber shall not be impacted by any external force, and shall not be knocked or slapped by hands. It shall not be stressed during moving and maintenance. It is prohibited to put anything on the vacuum circuit breaker to prevent the vacuum arc extinguishing chamber from being damaged when falling. Before delivery, the vacuum circuit breaker shall undergo strict parallelism inspection and assembly. During maintenance, all bolts of the arc extinguishing chamber shall be fastened to ensure uniform stress.

The vacuum circuit breaker interrupts the current and extinguishes the arc in the vacuum arc extinguishing chamber. However, the vacuum circuit breaker itself does not have a device to qualitatively and quantitatively monitor the vacuum degree characteristics, so the vacuum degree reduction fault is a hidden fault. At the same time, the vacuum degree reduction will seriously affect the vacuum circuit breaker’s ability to cut off the over-current, and lead to a sharp decline in the service life of the circuit breaker, which will lead to the switch explosion when serious.

To sum up, the main problem of the vacuum interrupter is that the vacuum degree is reduced. The main reasons for vacuum reduction are as follows.

(1) The vacuum circuit breaker is a delicate component. After leaving the factory, the electronic tube factory may have leakage of glass or ceramic seals after many times of transportation bumps, installation shocks, accidental collisions, etc.

(2) There are problems in the material or manufacturing process of the vacuum interrupter, and leakage points appear after multiple operations.

(3) For the split type vacuum circuit breaker, such as the electromagnetic operating mechanism, when operating, due to the large distance of the operating linkage, it directly affects the synchronization, bounce, overtravel and other characteristics of the switch to speed up the vacuum degree reduction. DC high-voltage generator

Treatment method for decreasing vacuum degree of vacuum interrupter:

Frequently observe the vacuum interrupter, and regularly use the vacuum tester of vacuum switch to measure the vacuum degree of the vacuum interrupter, so as to ensure that the vacuum degree of the vacuum interrupter is within the specified range; When the vacuum degree decreases, the vacuum interrupter must be replaced, and the characteristic tests such as stroke, synchronization and bounce must be done well.

3. Development of operating mechanism

Operating mechanism is one of the important aspects to evaluate the performance of vacuum circuit breaker. The main reason that affects the reliability of vacuum circuit breaker is the mechanical characteristics of operating mechanism. According to the development of operating mechanism, it can be divided into the following categories. DC high-voltage generator

3.1 Manual operating mechanism

The operating mechanism relying on direct closing is called manual operating mechanism, which is mainly used to operate circuit breakers with low voltage level and low rated breaking current. The manual mechanism has been rarely used in outdoor power departments except industrial and mining enterprises. The manual operating mechanism is simple in structure, does not require complex auxiliary equipment and has the disadvantage that it cannot automatically reclose and can only be operated locally, which is not safe enough. Therefore, the manual operating mechanism has almost been replaced by the spring operating mechanism with manual energy storage.

3.2 Electromagnetic operating mechanism

The operating mechanism that is closed by electromagnetic force is called electromagnetic operating mechanism d. CD17 mechanism is developed in coordination with domestic ZN28-12 products. In structure, it is also arranged in front of and behind the vacuum interrupter.

The advantages of the electromagnetic operating mechanism are simple mechanism, reliable operation and low manufacturing cost. The disadvantages are that the power consumed by the closing coil is too large, and it needs to be prepared [Overview of the development and characteristics of the vacuum circuit breaker]: The vacuum circuit breaker refers to the circuit breaker whose contacts are closed and opened in vacuum. Vacuum circuit breakers were initially studied by the United Kingdom and the United States, and then developed to Japan, Germany, the former Soviet Union and other countries. China began to study the theory of vacuum circuit breaker from 1959, and formally produced various vacuum circuit breakers in the early 1970s

Expensive batteries, large closing current, bulky structure, long operation time, and gradually reduced market share.

3.3 Spring operating mechanism DC high-voltage generator

The spring operating mechanism uses the stored energy spring as the power to make the switch realize closing action. It can be driven by manpower or small power AC and DC motors, so the closing power is basically not affected by external factors (such as power supply voltage, air pressure of air source, hydraulic pressure of hydraulic pressure source), which can not only achieve high closing speed, but also realize fast automatic repeated closing operation; In addition, compared with the electromagnetic operating mechanism, the spring operating mechanism has low cost and low price. It is the most commonly used operating mechanism in the vacuum circuit breaker, and its manufacturers are also more, which are constantly improving. CT17 and CT19 mechanisms are typical, and ZN28-17, VS1 and VGl are used with them.

Generally, the spring operating mechanism has hundreds of parts, and the transmission mechanism is relatively complex, with high failure rate, many moving parts and high manufacturing process requirements. In addition, the structure of the spring operating mechanism is complex, and there are many sliding friction surfaces, and most of them are in key parts. During long-term operation, the wear and corrosion of these parts, as well as the loss and curing of lubricants, will lead to operational errors. There are mainly the following shortcomings.

(1) The circuit breaker refuses to operate, that is, it sends operation signal to the circuit breaker without closing or opening.

(2) The switch cannot be closed or is disconnected after closing.

(3) In case of accident, relay protection action and circuit breaker cannot be disconnected.

(4) Burn out the closing coil.

Failure cause analysis of operating mechanism:

The circuit breaker refuses to operate, which may be caused by the loss of voltage or undervoltage of the operating voltage, the disconnection of the operating circuit, the disconnection of the closing coil or the opening coil, and the poor contact of the auxiliary switch contacts on the mechanism.

The switch cannot be closed or is opened after closing, which may be caused by undervoltage of the operating power supply, excessive contact travel of the moving contact of the circuit breaker, disconnection of the interlocking contact of the auxiliary switch, and too small amount of connection between the half shaft of the operating mechanism and the pawl;

During the accident, the relay protection action and the circuit breaker could not be disconnected. It may be that there are foreign matters in the opening iron core that prevented the iron core from acting flexibly, the opening tripping half shaft could not rotate flexibly, and the opening operation circuit was disconnected.

The possible reasons for burning the closing coil are: the DC contactor cannot be disconnected after closing, the auxiliary switch does not turn to the opening position after closing, and the auxiliary switch is loose.

3.4 Permanent magnet mechanism

The permanent magnet mechanism uses a new working principle to organically combine the electromagnetic mechanism with the permanent magnet, avoiding the adverse factors caused by mechanical tripping at the closing and opening position and the locking system. The holding force generated by the permanent magnet can keep the vacuum circuit breaker in the closing and opening positions when any mechanical energy is required. It is equipped with a control system to realize all the functions required by the vacuum circuit breaker. It can be mainly divided into two types: monostable permanent magnetic actuator and bistable permanent magnetic actuator. The working principle of bistable permanent magnetic actuator is that the opening and closing of the actuator depend on permanent magnetic force; The working principle of the monostable permanent magnet operating mechanism is to quickly open with the help of the energy storage spring and keep the opening position. Only closing can keep the permanent magnetic force. Trede Electric’s main product is the monostable permanent magnet actuator, and the domestic enterprises mainly develop the bistable permanent magnet actuator.

The structure of the bistable permanent magnet actuator varies, but there are only two kinds of principles: double coil type (symmetrical type) and single coil type (asymmetrical type). These two structures are briefly introduced below.

(1) Double coil permanent magnet mechanism

The double coil permanent magnet mechanism is characterized by: using permanent magnet to keep the vacuum circuit breaker at the opening and closing limit positions respectively, using excitation coil to push the iron core of the mechanism from the opening position to the closing position, and using another excitation coil to push the iron core of the mechanism from the closing position to the opening position. For example, ABB’s VMl switch mechanism adopts this structure.

(2) Single coil permanent magnet mechanism

The single coil permanent magnet mechanism also uses permanent magnets to keep the vacuum circuit breaker at the limit positions of opening and closing, but one exciting coil is used for opening and closing. There are also two excitation coils for opening and closing, but the two coils are on the same side, and the flow direction of the parallel coil is opposite. Its principle is the same as that of single coil permanent magnet mechanism. The closing energy mainly comes from the excitation coil, and the opening energy mainly comes from the opening spring. For example, the GVR column mounted vacuum circuit breaker launched by Whipp&Bourne Company in the UK adopts this mechanism.

According to the above characteristics of the permanent magnet mechanism, its advantages and disadvantages can be summarized. The advantages are that the structure is relatively simple, compared with the spring mechanism, its components are reduced by about 60%; With fewer components, the failure rate will also be reduced, so the reliability is high; Long service life of mechanism; Small size and light weight. The disadvantage is that in terms of opening characteristics, because the moving iron core participates in the opening movement, the motion inertia of the moving system increases significantly when opening, which is very unfavorable to improve the speed of rigid opening; Due to high operating power, it is limited by capacitor capacity.

4. Development of insulation structure

According to the statistics and analysis of the accident types in the operation of high-voltage circuit breakers in the national power system based on relevant historical data, the failure to open accounts for 22.67%; Refusal to cooperate accounted for 6.48%; The breaking and making accidents accounted for 9.07%; Insulation accidents accounted for 35.47%; Misoperation accident accounted for 7.02%; River closure accidents account for 7.95%; External force and other accidents accounted for 11.439 gross, of which insulation accidents and separation rejection accidents were the most prominent, accounting for about 60% of all accidents. Therefore, insulation structure is also a key point of vacuum circuit breaker. According to the changes and development of phase column insulation, it can be basically divided into three generations: air insulation, composite insulation, and solid sealed pole insulation.