Search

Insulation pollution flashover is one of the most common faults on the transmission and distribution lines, but a comprehensive theoretical explanation of the discharge mechanism and accurate prediction methods are lacking because of its complex surface discharge mechanism and numerous influencing factors. Current research mainly uses macroscopic analysis approaches such as empirical formulas and experimental testing, which cannot fully reveal the discharge mechanism of the formation and development process of local arc. To address this, this article introduces the energy level transition theory to calculate the critical condition for the development process of local arc and establishes a force analysis model based on the chain arc theory. Using this model, the evolution process of local arc shape is studied, and the effects of applied voltage, pollution degree, wind velocity, and wind direction on the floating arc shape are analyzed. In the validation experiment, the experimental values of the critical leakage current, local arc development time, and limit arc floating degree are consistent with the theoretical values. The research results can reveal the flashover mechanism of polluted insulation surface and provide theoretical support for accurate fault prediction and efficient operation and maintenance of power transmission and distribution equipment.

The detection of polluted insulator discharge in humid environments is crucial for power system examination. In this article, we propose novel classification and evaluation methods by using the spectral and thermal properties of different discharge states from pollution insulators under stable alternating current voltage. The discharge temperature of polluted insulators was measured using spectral analysis techniques. Faults were classified into four states based on leakage current and temperature thresholds, which were also related to the spectral properties of polluted substances. The results show that the salt density component Na of polluted insulators was easily excited, resulting in a visible light spectrum, while the component of nonsoluble deposit density (NSDD) Fe was also easily excited followed by Ca, leading to an ultraviolet spectrum. Under the first two fault states of polluted insulators, the leakage currents were both less than 10 mA, and the arc temperatures were below 1400 K. The arc temperatures in the last two fault states increased significantly. The characteristic light intensity weights of different fault states were calculated using a triangle calculation method. The proportion of ultraviolet light intensity in the last two fault states decreased significantly, while the proportion of visible light intensity increased. The numerical relationships between the excitation strength of different pollution substances with temperature and leakage current analyzed in this study will help in comprehensively understanding the complex physical and chemical processes of pollution discharge.

The study of dynamic temperature characteristics of cathode microprotrusion under electron emission would be essential to the development of high-voltage vacuum systems. Owing to the multiscale and multiphysics characteristics of the microprotrusions under the electron emission, smoothed particle hydrodynamics (SPH) method has become one of the feasible methods. In this article, the SPH method is introduced to study the dynamic temperature characteristics of a micrometer scale microprotrusion under the electron emission. First, the constitutive model and the equation of state with the material strength and the coupling effect of the heat conduction, Joule heating, Nottingham effect, and electron emission have been introduced into the SPH method. Then, an SPH model of the microprotrusion under the electron emission with considering the temperature correction is established by combining the SPH method and thermal-field emission heating model. Compared with the finite element method (FEM) and theoretical calculation, the SPH model of the microprotrusion under the electron emission is verified. Based on the SPH model of the microprotrusion, the dynamic temperature characteristics under the different conditions are quantitatively obtained and analyzed. The results of this article may provide some useful references for the vacuum insulation design and the insulation state evaluation of the high-voltage vacuum system.

Microprotrusions under high electric fields are considered to be sources of metal vapor and microplasma on metal electrode surfaces and may even initiate vacuum breakdown in vacuum gaps. The mechanism of the phenomena has been studied for a long time. However, the dynamic evolution processes of microprotrusions under high electric fields considering the influence of the material properties are still not clear. The objective of this article is to study the dynamic evolution processes of the nanoscale microprotrusions on Cu and Cr electrode surfaces under high electric fields based on atomistic modeling. With considering the electron emission heating, surface charge, Coulomb, and electric field forces, a 3-D numerical model is established by coupling molecular dynamics (MD) and finite difference method (FDM), for simulating the dynamic evolution processes of the microprotrusions under high electric field. Furthermore, the influence of material properties on the dynamic evolution processes is discussed and compared between Cu and Cr. The simulation results show that the heating effect of the electron emission induced by an intense electric field could lead the microprotrusions to localized melting and subsequent elongation and may finally generate metal vapor in the vacuum gap. In addition, the material properties have a significant influence on the field-induced dynamic evolution processes of microprotrusions.