Application and Analysis of Vacuum Circuit Breaker in Power System

This paper briefly describes the working principle and main structure of the vacuum circuit breaker and its characteristics. Through the analysis of the practicality of the vacuum circuit breaker in the substation field, the advantages and disadvantages and the faults and treatment methods that are easy to occur in the application are found, which provides a basis for the operation and maintenance of the vacuum circuit breaker.
Keywords: vacuum circuit breaker principle structural characteristics fault and treatment method
1 Overview

In the power system, the transformers, lines and other components on the substation need to be connected or withdrawn due to the failure of the inspection and modification operation mode, and thus some operations are performed. For example, under normal circumstances, it is necessary to reliably turn on and off the circuit. When changing the operation mode, it is necessary to flexibly perform the switching operation. In the case of a circuit failure, the fault current can be quickly removed, and the accident is limited to the local part. The area continues and the unfailed portion continues to operate to improve the reliability of the power system. In the event of power failure and isolation of the live parts during the maintenance of the equipment, to ensure the safety of the staff, etc., in order to complete the above operations, some switching appliances must be installed in the power system substation. It is one of the important equipments of the power system. Among them, the task of the circuit breaker is the most important and the most important, and its structure is also the most complicated, especially the high voltage circuit breaker is especially important.

A high voltage circuit breaker is a switching device that is used to turn the circuit on and off under normal conditions and automatically and quickly break the fault current in the event of a fault. Therefore, the basic requirement for it is: in each case, it should have sufficient breaking capacity, the shortest possible operating time and high working reliability. The most important task of the circuit breaker is to extinguish the arc, so all kinds of circuit breakers have different structure of arc extinguishing device, which greatly affects the arc extinguishing performance of the circuit breaker. According to the arc extinguishing medium and the principle of action adopted by the circuit breaker, the circuit breaker can be divided into the following types: oil circuit breaker, compressed air circuit breaker, SF6 circuit breaker, vacuum circuit breaker, self-produced gas circuit breaker and magnetic circuit breaker. Vacuum circuit breaker is a new type of circuit breaker developed in recent years. It is widely used in 10KV substation equipment. Vacuum circuit breaker uses vacuum as arc extinguishing medium and insulating medium. This paper introduces and analyzes vacuum circuit breaker.

2 working principle and main structure and characteristics of vacuum circuit breaker

2.1 Working principle of vacuum circuit breaker

The working principle of the vacuum circuit breaker is: when the moving and static contacts are opened under the action of the operating mechanism, an arc is generated between the contacts, and the surface of the contact volatilizes steam at a high temperature, because the contact is designed to have a special shape at the current When a magnetic field is generated, the arc moves rapidly along the tangential direction of the contact surface under the action of the magnetic field, and a part of the metal vapor is condensed on the metal cylinder (shield), and the arc is extinguished when the natural zero-crossing occurs, and between the contacts The strength of the medium quickly recovered.

2.2 The composition of the vacuum circuit breaker

The main structure of the vacuum circuit breaker is composed of a vacuum interrupter, an operating mechanism and an insulating support base.

2.2.1 Vacuum interrupter

According to the switch type, there are external shield type ceramic vacuum interrupter, intermediate sealing cup-shaped longitudinal magnetic field miniaturized vacuum interrupter, and inner sealed glass bubble interrupter. The basic structure is as follows:

1 airtight insulation system (outer casing)

The hermetic insulation system consisting of a gas-tight insulating cylinder made of ceramic, glass or glass-ceramic, a movable end cover, a fixed end cover, and a stainless steel bellows is a vacuum-tight container. In order to ensure airtightness, in addition to the strict operation process in the sealing type, the material itself is required to have a gas permeability and a small amount of internal air release.

2 conductive system

It consists of a fixed conductive rod, a fixed running surface, a fixed contact, a moving contact, a moving running surface, and a moving conductive rod. There are roughly three types of contact structures: cylindrical contacts, transverse magnetic field contacts with spiral groove running surfaces, and longitudinal magnetic field contacts. At present, the longitudinal magnetic field technology is adopted, and the arc extinguishing chamber has a strong and stable arc breaking capability.

3 shielding system

The shield is an indispensable component in the vacuum interrupter, and has a plurality of main shields, bellows shields, and shroud shields for the contacts. The function of the main shield is to prevent the arc product from splashing onto the inner wall of the insulating casing during the arcing process, thereby reducing the insulation strength of the casing. b Improve the uniformity of the electric field distribution inside the arc extinguishing chamber, which is beneficial to reduce the local field strength and promote the miniaturization of the vacuum interrupter. c Condensing the arc product, absorbing a part of the arc energy, and contributing to the recovery of the strength of the medium after the arc gap.

2.2.2 Operating mechanism of the circuit breaker

The operating mechanism used is different depending on the type of circuit breaker. Commonly used operating mechanisms include spring operating mechanism, CD10 electromagnetic operating mechanism, CD17 electromagnetic operating mechanism, CT19 spring energy storage operating mechanism, and CT8 spring energy storage operating mechanism.

2.2.3 Other components: base, insulation support, insulators, etc.

2.3 vacuum circuit breaker features the following

1 The contact opening distance is small, the contact opening distance of the 10KV vacuum circuit breaker is only about 10mm, the operating work of the operating mechanism is small, the mechanical part stroke is small, and the mechanical life is long.
2 arcing time is short, and has nothing to do with the size of the switch current, generally only half cycle.
3 After the arc is extinguished, the contact gap medium recovery speed is fast, and the fault performance of the near-breaking near-zone is better.
4Because the amount of wear during the breaking current is small, the electrical life of the contact is long, the full capacity is interrupted for 30-50 times, the rated current is interrupted for more than 5000 times, and the noise is small for frequent operation.
5 small in size and light in weight.
6 is suitable for breaking capacitive load current.

Because of its many advantages, it is widely used in substations. The current models mainly include: ZN12-10, ZN28A-10, ZN65A-12, ZN12A-12, VS1, ZN30.

3 Commonly occurring faults and treatment methods in vacuum circuit breaker applications

Vacuum circuit breakers have many advantages, so they are used in many substations. Due to the use of special vacuum elements, the failure of the arc extinguishing chamber portion is significantly reduced as the manufacturing level has increased in recent years. The vacuum interrupter does not require maintenance, and when it is damaged, it can only be replaced. The faults occurring during the operation of the vacuum circuit breaker account for a large proportion of the operating mechanism, followed by the primary conductive portion, the conductive rod of the contact, and the like. The following analysis and processing of the faults that often occur in vacuum circuit breakers have the following aspects:

3.1 Reduced vacuum

The vacuum degree of the vacuum interrupter in operation is lower than 6.6x10-2pa, and the new vacuum interrupter of the factory is lower than 7.5x10-4pa, which is unqualified. The reason for the decrease of vacuum is: vacuum interrupter leakage Gas, mainly due to tight welds or tiny leaks in the seal.

The metal material inside the vacuum interrupter is released with gas. In this case, the vacuum is lowered for a period of time during the first several discharges of the vacuum interrupter, and the vacuum is maintained at a certain level after the trace gas is exhausted.

Common methods for checking the degree of vacuum:

1 spark meter method: This method is simple, only can be qualitatively checked, let the spark gauge touch the wire on the surface of the switch tube, observe the light inside the tube. If it is light cyan, it can be judged that the vacuum is qualified. If it is red and blue, it can be judged. The arc chute has failed and this method is not suitable for ceramic enclosures.
2 Observe the arc light when the current is interrupted. Normally, it should be light cyan. If the arc is purple, it can be judged that the arc extinguishing chamber has failed.
3 power frequency withstand voltage method: for the 10KV vacuum switch tube in the fracture plus 42KV1min power frequency voltage should be qualified.
4 Vacuum degree tester method: After the vacuum degree is reduced, the vacuum interrupter should be replaced.

3.2 arc chamber contact electrical wear

After the contact surface of the vacuum interrupter contacts is subjected to multiple breaking currents, it will gradually be abraded by wear (commonly called electric wear). The contact thickness is reduced, the stroke of the bellows becomes larger, and the contact resistance is increased. Arc performance and electrical conductivity can have an adverse effect. The change in the overtravel of the switch during maintenance is the electrical wear of the contact. When the electrical wear value reaches the manufacturer's specifications, the arc extinguishing chamber cannot continue to be used. Electrical wear can be used to check the change of the length of the conductive rod of the arc extinguishing chamber. If the variation exceeds 3mm, the wear is serious. The qualitative method can also be used to measure the contact resistance. Generally, the measured value is not greater than the factory value. 1.2 times. Treatment method: The electrical contact of the contact is severe. When the specified value is reached or exceeded, the vacuum tube must be replaced and replaced with three phases. If the specification is not exceeded or the contact resistance is significantly increased but the specified value is not exceeded, the contact gap can be adjusted and used. However, the vacuum of the arc extinguishing chamber should be measured. If the arc extinguishing chamber does not meet the requirements, it should be replaced.

3.3 Vacuum circuit breaker rejection reasons and search methods

3.3.1 Electrical circuit failure

1 DC voltage is too low; 2 operation insurance and trip circuit components are in poor contact or short-term;

3 The trip coil is disconnected; 4 switch low voltage is unqualified; 5 car or switch interlock contact is poor.

3.3.2 Mechanical loop failure

1 three-plate three-point too low; 2 tripping ejector pinning or falling off; 3 closing buffer offset, roller and bumper stuck. Search method: When the electric trip fails, it should first judge whether it is an electrical loop fault or a mechanical loop fault. When the jack iron core does not move, it means that it is a trip circuit, otherwise it is a mechanical loop fault, and then further find out the cause. When the switch is found to be out of order, it should be manually opened.

3.4 Vacuum circuit breakers refuse to join and cause jumps and treatment methods

3.4.1 The length of the closing iron core rod of the electromagnetic operating mechanism is not enough. The length of the iron core rod should be adjusted so that the gap between the roller and the bracket meets the requirement of 2±0.5mm.
3.4.2 The auxiliary switch is disconnected too early. At this time, adjust the length of the auxiliary switch lever to open it after the breaker contacts are closed.
3.4.3 Spring energy storage operation mechanism The closing spring limit is unreliable and the closing is not in place. The closing spring energy storage ends, but the motor potential cannot be cut off.
3.5 spring energy storage switch can not be gated
3.5.1 The closing spring power is not enough, replace the closing spring.
3.5.2 When the switch is closed, it is in the semi-divided and semi-closed state. Adjust the gap between the cam and the roller to increase it, and adjust the overtravel to reduce it.

4 Conclusion

This paper analyzes the characteristics and main structure of the vacuum circuit breaker. Because the vacuum circuit breaker has the advantages of high breaking capacity, strong arc extinguishing ability, long service life, simple structure and convenient maintenance, it is widely used in the power system and shows its huge Advantages: Vacuum circuit breakers have an absolute advantage in high-voltage circuit breakers with a voltage rating of 10KV. These switches are used in our substations. However, it is known from the introduction of this paper that vacuum circuit breakers are also prone to some faults, and maintenance personnel should master these treatment methods to ensure safe production and reliable power supply.