SF6 Circuit Breaker

High-voltage SF6 circuit breaker is an important component in power grid, which has an important impact on the reliability of power grid operation.

1. When electrons and SF6 molecules are in contact, almost 100% of them are mixed to form heavy negative ions, which has great value for the deionization and extinguishing of the residual arc column. 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.

2, SF6 gas excellent insulation and arc extinguishing performance, so that SF6 circuit breaker has the following advantages: strong breaking ability, fracture voltage is suitable for doing higher, allow continuous breaking more 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. It is used more and more in high voltage circuit.

Commonly used SF6 circuit breakers are LN1-35 type, HB36 type two.

Pure SF6 gas is a good arc extinguishing medium. If it is used in low-voltage electrical appliances with frequent operation, due to the arc action of frequent operation, metal vapor reacts with SF6 gas decomposition, and combines to form fine powder with good insulation (hydrofluorate, sulpiate, etc.), which is deposited on the surface of the contact and seriously corrodes the contact material, resulting in a sharp increase in contact resistance. The sealed contact filled with SF6 gas cannot work reliably. Therefore, SF6 is not suitable for frequent operation of low-voltage electrical appliances as an arc extinguishing medium.

Because SF6 gas will decompose corrosive gas at high temperature during discharge, it has a serious corrosion effect on aluminum alloy, and also damages phenolic resin laminate materials and porcelain insulation. If the SF6 and N2 are mixed, when the SF6 content exceeds 20% to 30%, the insulation strength has been the same as the insulation strength when fully filled with SF6, and the corrosion is greatly reduced, so SF6 often mixed N2 is used, in the SF6 circuit breaker, the water content of SF6 gas must be strictly stipulated not to exceed the standard. Water and SF4 in the arc decomposition produce hydrofluoric acid (H2O+SF4→SOF2+2HF), which corrodes the material. When the moisture content reaches saturation, it will also condense on the surface of the insulation, which significantly reduces the insulation strength and even causes surface discharge. The operating experience and the above analysis show that: SF6 circuit breaker due to the small volume of insulation structure, if the water content of SF6 gas is high, the insulation level will be greatly reduced, the contact resistance will increase sharply, and damage or explosion accidents are prone to occur during operation. Therefore, each manufacturer and operating department require a strict sealing process, and the water content of SF6 gas shall not exceed the standard. China's standard is that the water content of SF6 gas should be less than 300ppm (volume ratio).

SF6 circuit breaker uses SF6 gas as arc extinguishing medium. Under normal circumstances, SF6 is a non-flammable, odorless, non-toxic inert gas, about five times as dense as air. However, under the action of the arc, a small part of SF6 gas will be decomposed and generate some toxic low fluoride, such as SOF2, SF4, SOF4 and SO2F2, which has an impact on body health and corrosion and deterioration of metal parts. Therefore, in the SF6 circuit breaker, the adsorption device is generally installed, and the adsorbent is activated alumina, activated carbon and molecular sieve. The adsorption device can completely adsorb the toxic substance generated by the decomposition of SF4 gas at high temperature of the arc.