纳秒脉冲下真空中绝缘子表面带电特性

Surface charge characteristics on insulators in vacuum under nanosecond pulse excitation

实验研究了前沿50 ns、脉宽350 ns和3μs正负极性的4种脉冲电压作用下,真空中绝缘材料的各种局部放电现象以及由此引起的表面带电。结果表明:在脉冲电压作用下,绝缘材料沿面闪络发生前会发生各种局部放电现象,局部放电是纳秒脉冲下绝缘材料表面带电的根本原因。只要发生局部放电,绝缘材料表面就会出现正极性的电荷,并且在阴极附近的电荷密度略大于阳极附近的电荷密度,但由于材料陷阱的分布,也会有局部突变。有机玻璃比聚乙烯容易发生局部放电和积聚电荷,沿面闪络电压值更低。局部放电引起表面带电的物理机制是二次电子发射形成过程中的电子碰撞电离和材料陷阱捕获电荷共同作用。

Various partial discharge of an organic and a polyethylene insulation materials in vacuum under impulse voltage （rise time of 50 ns, halt＇width of 350 ns and 3μs） excitations were observed, and the characteristics of surface charge were investigated by an electrostatic probe, a current monitor system and a luminescence signal measurement system. The experimental results show that, a partial discharge current may be observed near the peak, the tail of pulse, or even close to zero voltage at pulse end. The partial discharge is the basic reason for the surface charge under nanosecond pulse excitations. Positive surface charge was measured after the partial discharge happen, and the charge density near cathode is alittle more than that near anode for the electron emission began from the cathode. The partial discharge and surface charge on organic glass are easier been observed than those on polyethylene, and the organic glass insulator flashover voltage is lower. The partial discharge induces the surface charge, whose physical mechanism is the trap centers of insulator and the collisional ionization during the process of the secondary electron emission avalanche.