Tungsten Copper Contact Used for SF6 Circuit Breaker

SF6 circuit breaker uses SF6 gas as dielectric medium. Compared with conventional air circuit breaker, it also belongs to air blast circuit breaker. But there are some differences, such as lower working pressure, in the process of blowing the arc, and gas is not discharged to the atmosphere, but in a closed loop system used. Due to the perfect insulation and interrupter properties of SF6 gas, SF6 circuit breaker has many advantages, such as good breaking ability, high voltage suitable for fracture, allow continuous breaking more frequently, small in noise, no security threat, small electro-mechanical wear and so on which is a king of “maintenance-free” circuit breaker with excellent performance and has been widely used in high-voltage circuit. As the voltage level of the SF6 circuit breakers imposed increasingly higher and higher, the requirements of physical and electrical performance is also increasing.

In general, SF6 circuit breakers should meet the design requirements that the hardness of contact > HRB 82, the density > 13g / cm3, the conductivity ≥ 50% IACS, and after a 20-time All-breaking capacity test, the contact surface burning amount should not exceed 3mm. Conventional ratio has two kinds of W-Cu40 and W-Cu 35, wherein the content of W should not be too high (≤70%), otherwise the burning rate will increase. First of all, choose fine W powder is beneficial for reducing the burning rate, but too fine W powder will make liquid copper difficult infiltrate and easily form crumb defects on the matrix. Adding sintering additives will remarkably decrease the electrical conductivity and the burning loss has an increasing trend on the surface of contacts after cut-off. In addition, the granularity composition also needs a proper mixing ratio; viewed from the manufacturing process, add proper amount of induced Cu powder when mixing; leave some place for re-press when compacting; the volume of liquid copper must be equal to tungsten skeleton pore volume during sintering infiltration and it should be surface cleaned after cooling.

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