基金项目:
国家自然科学基金项目(51907168);
国家轨道交通电气化与自动化工程技术研究中心开放课题重点项目(NEEC-2019-A01);
国家电网公司科技项目(521104190007);
Project Supported by National Natural Science Foundation of China (51507146);
National Rail Transit Electrification and Automation Engineering Technology Research Center Open Project (NEEC-2019-A01);
Science and Technology Project of State Grid Corporation (521104190007);
Insulation equipment on the roof of high-speed trains will cause frictional charging and collision charging with fine particles such as dust and metal particles in the airflow environment, and form surface charges on their surfaces, causing surface discharge phenomena, which will threaten the stability of train power supply in severe cases. In order to study the influence of the airflow on the surface charge dissipation characteristics, a test platform for surface charge accumulation in the airflow environment was built, and the dissipation law of surface charge under different air flow speeds was measured. The mechanism of surface charge conduction in the airflow environment was discussed. The results show that the airflow environment will accelerate the dissipation of surface charges, and the greater the airflow velocity, the faster the dissipation. The surface charge dissipation under the airflow environment is mainly affected by the gas-side recombination and the thin-film conduction dissipation mechanism on the surface of the medium. As the airflow velocity increases for the gas-side neutralization conduction mechanism, the reduced air density leads to an increase in the average free path of gas molecules and the ion mobility and ion concentration in the air increase, which intensifies the rate of surface charge neutralization and dissipation through the gas side. For the thin layer conduction on the surface of the medium, the air flow will rub the surface of the insulating medium and cause a temperature rise, which affects the trapping/detrapping process of the carrier. It mainlyshows that the trap capture cross-section decreases, and the probability of carrier detrapping increases. As the airflow speed increases, the depth of the trap level continues to decrease, making carriers easier to detrap.
KEY WORDS :airflow environment;surface charge dissipation;conduction mechanism;trap level;
长期以来,国内外学者从电荷的积聚、电荷的消散以及表面的电荷输运特性等方面对绝缘材料的表面电位/电荷衰减特性以及绝缘介质表面电荷积聚机理开展了广泛的研究,并提出了各种模型和假设来描述表面电荷动力学过程。在绝缘材料表面电荷积聚方面主要有如下几种模型:体积电导模型[6]、法向场强模型[7]、切向场强模型以及空间电荷输运模型[8]。日本学者Iwabuchi测量了绝缘子的电荷密度分布及电导率,实测数据表明,表面电导的不均匀是引起电荷积聚的主要因素[9];德国学者Kindersberger等模拟气体中绝缘子表面电荷的衰减,并通过试验验证提出了表面电荷消散的3种物理机制:1)通过绝缘介质体传导;2)通过绝缘介质面传导;3)通过气体侧离子的复合[10-11]。实际工况下,3种机制是同时作用的,且不同工况下,占主导地位的消散机制不同。影响表面电荷消散的因素很多,包括环境因素(如气体氛围、压强、温度等)、材料本征性质等。Shahid Alam研究了不同类型硅橡胶片的表面电势衰减,通过实验和计算机模拟的方法,研究了固体材料中体积和表面导电的影响,并根据材料表面电势衰减特性推导出与场强有关的体电导率[12]。Sarath Kumara等对电晕充电的HTV硅橡胶表面电势衰减进行了实验研究,气体复合作用的增强是由于附近电晕提供的周围空气中游离离子的增加[13]。载流子一旦被陷阱中心捕获,载流子就存在脱陷行为,因此也有大量学者对载流子的入陷/脱陷动力学过程进行研究。S. Le Roy等人将表面电荷的消散分为了3个阶段:第I阶段主要是电荷捕获和去捕获过程;第III阶段以电荷传导为主;阶段II由I和III两个过程共同决定[14]。天津大学杜伯学等开展了材料温度对电荷衰减曲线的影响[15]。西安交通大学闵道敏、李盛涛等人基于陷阱调整机制的电荷输运模型,通过仿真计算了体陷阱深度对电荷密度和电场分布的影响,并获得了陷阱参数对电荷输运的影响规律,同时对基于空
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