高压SF_6断路器非平衡态等离子体电弧的熄弧特性

Extinction Characteristics of Non-equilibrium Plasma Arc in High-voltage SF_6 Circuit Breaker

SF6高压断路器开断过程是结合电弧特性、压气特性、气流特性、电磁特性、温度特性、介质恢复特性等的多物理动态过程。为避免其熄弧重燃,考虑电弧能量对等离子体内电子温度和重粒子温度的动态作用的情况下,建立了SF6气体电弧等离子体非平衡态双温度电弧数学模型。计算得出了等离子体中各粒子密度随电子和重粒子温度变化曲线,带电粒子密度随温度和压强的变化趋势,以及非平衡态等离子体电导率在不同压强下随温度变化的曲线。通过126 kV断路器负载开断过程压气特性和气流特性计算,得到了熄弧过程中灭弧室内的压强、温度和密度分布。考虑空间电荷对灭弧室内电场分布的影响,计算了气流运动过程中的电场分布,计算了熄弧过程中介质恢复特性分布,分析了电弧等离子体熄灭动态过程中微观参数的变化情况。计算表明:1 600 A燃弧2 ms小电流电弧开断弧后0.2 ms内介质恢复平均速度为175 kV/ms,明显快于电压恢复速度37.7 kV/ms;开断速度对不同燃弧时间下的介质恢复特性有直接的影响,燃弧时间越短越容易发生重燃弧现象;燃弧时间<2 ms时,开断速度为11 m/s的击穿裕度值较大,可以保证弧后不会发生重燃弧现象。

The interrupting action of high-voltage SF6 circuit breaker is a multi-physics process involving arc, flow, elec-tromagnetic field, temperature, pressure, and dielectric recovery. To protect the breaker fi＇om reignition after arc extinction,taking into account the dynamic effect of arc energy on the electron temperature and heavy particle temperature in arcplasma, we built a dual-temperature mathematical model to describe non-equilibrium plasma in small-current SF6 arc.Densities of particles in plasma varying with electron temperature and heavy particle temperature, as well as the conduc-tivity of non-equilibrium plasma under different temperatures and pressures, were calculated and analyzed. Then, wecalculated the pressure and flow in the interrupting process of a 126 kV circuit breaker with load, and obtained the distri-bution of pressure, temperature, and electron density in the arc chute. Finally, considering the effect of special charge onthe electric field distribution in the arc chute, we calculated the electric field with air flow, the dielectric recovery in theinterrupting process, and hence analyzed the parameter changes during the arc extinction duration. The calculation resultsindicate that 0.2 ms after a 1 600 A current burnt for 2 ms being extinguished, the average dielectric recovery rate is 175kV/ms, significantly faster than the rate of voltage recovery, 37.7 kV/ms. The breaker＇s opening speed directly affects thedielectric recovery under different arcing times, and the shorter arcing time would more easily lead to reignition. Whenarcing time is less than 2 ms and breaking speed is 11 m/s, critical breakdown voltage is greater than TRV, which indicatesa large safe margin and reliably avoids reignition.