What is sulfur hexafluoride circuit breaker used for? How does it work?- SF6在线监测系统_SF6检漏仪_SF6传感器_SF6密度继电器

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What is sulfur hexafluoride circuit breaker used for? How does it work?

发布时间：2024-07-05 来源：ydlcb 浏览次数：24次

SF6 gas with excellent arc extinguishing performance and insulation performance is used as the circuit breaker of arc extinguishing medium, called SF6 circuit breaker, which is widely used in power system. Suitable for frequent operation and high-speed breaking occasions, it is recommended to use SF6 circuit breakers in 7.2-40.5 in China, especially almost all SF6 circuit breakers above 126KV. But not at high altitudes.

SF6 circuit breaker can not only cut off and connect high-voltage lines and various no-load and load currents during the normal operation of the system, but also automatically, quickly and reliably cut off various overload currents and short-circuit currents through the role of relay protection devices when the system fails to prevent the occurrence and expansion of the accident range.

A circuit breaker using sulfur hexafluoride (SF6) gas as arc extinguishing medium and insulating medium, referred to as SF6 circuit breaker. It belongs to the same air-blown circuit breaker as the air circuit breaker, the difference is:

① The working pressure is low;

In the arc blowing process, the gas is not discharged to the atmosphere, but is recycled in a closed system. The use of sulfur hexafluoride as an arc extinguishing medium in circuit breakers began in the early 1950s. Due to the excellent characteristics of this gas, the single break of this circuit breaker is much higher than the compressed air circuit breaker and less oil circuit breaker in terms of voltage and current parameters, and does not require high air pressure and a considerable number of series breaks. In the 1960s and 1970s,SF6 circuit breakers have been widely used in ultra-high voltage and large capacity power systems. In the early 1980s, SF6 circuit breakers with 363 kV single break, 550 kV double break and rated breaking current of 80 and 100 kV were successfully developed.

SF6 circuit breakers use sulfur hexafluoride density relays to monitor changes in gas pressure. When the sulfur hexafluoride gas pressure drops to the first alarm value, the density relay operates and gives a signal of the gas pressure. When the sulfur hexafluoride gas pressure drops to the second alarm value, the density relay operates, reports the signal of the locking pressure, and disconnects the switch's jump circuit to realize the opening and closing of the lock.

At below 150 ° C,SF6 has good chemical inertness and does not chemically interact with metals, plastics and other materials commonly used in circuit breakers. When it is decomposed into various components at high temperatures caused by high-power arc, it will be synthesized again within a very short time after the arc is extinguished. There is no carbon in SF6 and no air exists to avoid contact oxidation. The dielectric strength of SF6 is very high and increases with the increase of pressure. At 1 atmosphere pressure, the dielectric strength of SF6 is about 2 to 3 times that of air. When the absolute pressure is 3 atmospheres, the dielectric strength of SF6 can reach or exceed that of common insulating oils. SF6 arc extinguishing performance is good, in a simple break of the arc extinguishing chamber, its arc extinguishing capacity is 100 times larger than air. In SF6, when the arc current is close to zero, there is only a very high temperature in the center of the arc column with a very small diameter, and a non-conductive layer around it. In this way, the dielectric strength of arc gap will recover quickly after the current crossing zero.

SF6 circuit breaker has two structural layout forms, one is porcelain pillar structure. The circuit breaker consists of three independent single-phase and a hydraulic and electrical control cabinet. Each phase consists of four arc-extinguishing chambers (fractures) connected in series by two pillar porcelain sleeves. Both the interrupter chamber and the pillar porcelain sleeve are filled with SF6 gas at rated pressure. The second is the tank structure. The circuit breaker adopts bidirectional longitudinal blowing type arc extinguishing chamber. When opening, the cylinder and the moving contact are driven by the transmission mechanism of the arm box.

The molecules and free electrons of SF6 have very good miscibility. When the electrons and SF6 molecules are in contact, almost 100% of them are mixed to form heavy negative ions, which has great value for deionization and arc extinguishing of residual arc columns. That is, SF6 has good electronegativity, and its molecules can quickly capture free electrons and form negative ions. The conduction effect of these negative ions is very slow, which accelerates the recovery rate of the arc gap medium strength, so it has a good arc extinguishing performance. Under the pressure of 1.01×105Pa, the arc extinguishing performance of SF6 is 100 times that of air, and it does not deteriorate after arc extinguishing and can be reused. SF6 gas excellent insulation and arc extinguishing performance, so that SF6 circuit breaker has the following advantages: strong breaking ability, break voltage to do higher, allow more continuous breaking times, suitable for frequent operation, low noise, no fire danger, mechanical and electrical wear is small, is an excellent performance of "no maintenance" circuit breaker.

With the rapid development of the national economy, the demand for electricity in all walks of life has also increased sharply, the load of the power system is growing day by day, and the reliability of power supply is gradually improved. The switch of the substation is gradually replaced by the oil switch into a new type of SF6 circuit breaker, which has been widely used in the power system.

First, sulfur hexafluoride circuit breaker work introduction:

Sulfur hexafluoride circuit breaker is a new type of circuit breaker which uses sulfur hexafluoride gas as insulating medium and arc extinguishing medium. Sulfur hexafluoride gas is colorless, tasteless, non-toxic, non-flammable inert gas, with high electrical strength and good arc extinguishing performance, dielectric strength far exceeds the traditional insulating gas. Therefore, it is used in electrical equipment, which can reduce the size of equipment, eliminate fires, and improve the reliability and safety of the power system.

Second, sulfur hexafluoride circuit breaker structure:

Sulfur hexafluoride circuit breaker: by the body structure (using a three-box structure), operating mechanism, arc extinguishing device composed of three parts. It has the advantages of simple structure, small size, light weight, large breaking capacity, rapid arc extinguishing, many allowable breaking times, long maintenance cycle, etc., and it is the direction of popularization and application of power system in the future.

Three, sulfur hexafluoride circuit breaker working principle:

The sulfur hexafluoride circuit breaker is often filled with 3 to 5 atmospheres of sulfur hexafluoride gas as the internal insulation of the circuit breaker. In the process of breaking the circuit breaker, the piston is driven by the moving contact to form an air flow used to blow off the arc.

The basic structure of the sulfur hexafluoride circuit breaker interrupter chamber is connected by a moving contact, an insulating nozzle and a pressure piston, which is driven by an operating mechanism through an insulating connecting rod. The fixed contact is made of tube shape, the moving contact is a socket type, and the end of the moving and fixed contact are inlaid with copper tungsten alloy. The insulated nozzle is made of high temperature and corrosion resistant polytetrafluoroethylene.

When the circuit breaker is opened, the moving contact and the piston move to the right together. The arc is generated after the moving and fixed contacts are separated. When the piston moves rapidly to the right, the gas on the right side is compressed, and the air flow is generated through the nozzle to blow the arc and extinguish the arc. Thereafter, the gas in the extinguishing chamber is discharged into the switch body through the inner hole of the fixed contact and the cooler.

When the circuit breaker is closed, the operating mechanism drives the moving contact, nozzle and piston to the left, so that the fixed contact is inserted into the moving contact seat, so that the moving contact and the fixed contact have good electrical contact to achieve the purpose of closing.

The sulfur hexafluoride switch uses the sulfur hexafluoride density relay to monitor the change of gas pressure. When the sulfur hexafluoride gas pressure drops to the first alarm value, the density relay operates and gives a signal of the gas pressure. When the sulfur hexafluoride gas pressure drops to the second alarm value, the density relay operates, reports the signal of the locking pressure, and disconnects the switch's jump circuit to realize the opening and closing of the lock.