真空灭弧室关合容性电流预击穿高频涌流电弧影响触头熔焊断裂形貌的机理

If a capacitive load is switched in by a vacuum interrupter, a prestrike high frequency inrush current arc causes a local contact surface melting and welding during a making operation. A crater on one contact surface and a protrusion on the opposite contact surface in a range of millimetre level are formed because of a rupture of the contact welding during the breaking operation. Even though there is a small power frequency current in the breaking operation, the arc cannot modify the contact surfaces efficiently. Therefore the dielectric recovery strength after power frequency current zero in vacuum is mainly determined by the destroyed contact surfaces that have an important influence on the restrike phenomena. Thus, the objective of this project is to investigate an impact of prestrike high frequency inrush current arc on contact welding and rupture in vacuum interrupters. First, an experimental work will be done to understand the evolution of the high frequency inrush current arc during the prestrike process based on a capacitive load switching circuit.The high frequency inrush current arc will be observed under various amplitudes and frequencies of inrush current, contact materials and closing speeds. A prestrike arc model will be built up on a basis of magnetohydrodynamics. Second, the constricted high frequency inrush current arc will shorten its length in the making operation. It will heat a local contact surface. The heating and welding process will be determined by the proposed arc model. Third, the contact welding rupture pattern will be explained by a material fracture mechanics theory, which helps to reveal the mechanism of contact rupture pattern formation. The results will provide a theoretical supporting to reduce the restrike probability of vacuum interrupters in switching capacitive loads.

真空灭弧室投切容性负载时，合闸预击穿过程中产生的高频涌流电弧会严重烧蚀触头局部表面并造成熔焊，随后分闸过程引起触头熔焊区断裂并产生毫米级的熔坑及突起，而在分闸燃弧过程中的工频小电流不会显著改变触头表面形貌，被破坏的触头表面决定了工频电流过零后的真空介质恢复强度，从而对重击穿现象产生重要影响。因此本项目拟研究真空灭弧室关合容性电流合闸预击穿高频涌流电弧影响触头熔焊断裂形貌的机理。首先，基于已建立的真空灭弧室容性负载投切实验回路，在不同涌流幅值和频率、触头材料以及合闸速度条件下，实验研究预击穿过程中高频涌流电弧的发展规律，建立合闸预击穿电弧的磁流体动力学模型；进而研究在开距逐渐减小情况下的集聚态高频涌流电弧对触头表面的传热及熔焊规律；最后采用材料断裂力学理论研究熔焊点拉开破裂后触头表面的形貌特征，并解释触头表面形貌破坏的形成机理。研究结果将为降低真空灭弧室投切容性负载的重击穿概率提供理论依据。

真空灭弧室因其优异特性非常适合投切容性负载。但较高电压等级下，真空灭弧室投切容性负载会存在较高重击穿概率问题。合闸预击穿过程中产生的高频涌流对触头表面的破坏是影响真空灭弧室容性负载投切中重击穿概率的最重要因素。但过去的真空灭弧室容性投切技术研究多集中在开断后重击穿现象研究，重点并未放在合闸预击穿过程。本项目系统研究了真空灭弧室关合容性电流预击穿过程中高频涌流电弧特性及高频涌流电弧影响触头熔焊断裂形貌的机理。首先，通过实验研究了触头材料和磁场对预击穿过程中高频涌流电弧特性和涌流电弧烧蚀后触头熔焊特性的影响规律。该结果可为研制适用于高电压等级容性电流开断的真空灭弧室触头选型提供参考。其次，针对40.5kV真空灭弧室在不同配比和制备工艺触头材料进行容性电流关合时的预击穿特性展开了研究。根据预击穿发生时刻击穿电压特性的不同，提出了三种触头间隙击穿类型，并详细分析了三种触头间隙击穿现象各自可能的发生机理。这对深入理解预击穿过程具有重要意义。第三，研究了预击穿涌流对工频电压下场致发射电流的影响规律。得到了工频电压下场致发射电流特性及场致发射电流对触头表面微观形貌影响规律。第四，运用分形理论量化分析了涌流烧蚀熔焊区域断裂后触头表面形貌特征，确定了不同触头材料真空灭弧室关合容性电流预击穿高频涌流电弧影响触头表面形貌形成规律。第五，基于实验结果，运用PIC-MCC方法建立了真空灭弧室预击穿电弧动力学模型，从仿真的角度来分析了合闸预击穿电弧对真空断路器容性电流开断过程中的重击穿现象的影响作用机理。最后，介绍了项目相关研究成果应用。本项目研究成果对于深入理解真空灭弧室关合容性电流预击穿高频涌流电弧对触头表面状态影响机理具有重要意义，并为降低真空灭弧室投切容性负载的重击穿概率提供理论依据和技术支撑。