In this study, the motion behavior of micron-sized metal particle swarm in case of flow-electric field coupling is observed in a non-contact manner based on the experiments. According to the results of observation, the charging characteristics of metal particle swarm in insulating oil flow under DC electric field are analyzed in detail, and the effects of electric field intensity, voltage type and oil flow velocity on the charging process and motion of particle swarm are studied. The obtained results show that the applied electric field will cause the streamlines of velocity of the metal particles to oscillate along its direction, where such effect becomes more obvious as the electric field intensity increases. The increase of oil flow velocity can weaken the influence of electric field and make the streamlines of velocity tend to be flat. The oscillation effect of streamlines of velocity under AC electric field is much weaker than that of DC electric field. In addition, based on the measured kinetic parameters of particles, it is found that the charge quantity of the moving particles in the gap of electrodes has the characteristics of temporal and spatial variations, and the particles have a variety of charging modes, including collisional charging, charge transfer, neutralization and accumulation. High velocity of flow and the alternating electric field hinder the charge transfer between particles, resulting in a decrease in the overall charge of the particle swarm. Finally, from the perspective of micro-discharge and electric field distortion, we explain the influence mechanism of flow velocity and voltage type on the discharge characteristics of oil flow containing metal impurities.

In order to guide the design of effective shielding layer to reduce the risk of dielectric electrostatic discharge in high-power and high-voltage spacecraft under GEO environment, it is necessary to explore the influence of grounding method and the joint action of high working voltage and deposited charge on the deep dielectric charging characteristics. In this article, based on the FLUMIC3 model, the electron flux of GEO environment is calculated, and an assessment method for the dielectric electrostatic discharge risk is established by combining Geant4 and a finite element method. Then, this method is used to calculate and analyze the influence of the grounding method and operating voltage on the electric field distribution of the polyimide under different shielding thicknesses. The results show that increasing the shielding thickness and grounding area can effectively reduce the polyimide internal electric field, and the aluminum shielding safety threshold required under the worst conditions is 2.920 mm; the influence of the working voltage mainly depends on the application method and the voltage value. During the working voltage increase from 100 to 5000 V, assume the working voltage ( V _s ) is applied to one side of the polyimide sample, when the other side is suspended, namely, not grounded (B, V _s -S; C, S- V _s ), the maximum electric field depends on the deposited charge and it does not change with the working voltage; when the other side of the sample is grounded (A, V _s -G; D, G- V _s ), the maximum electric field and its distribution are determined by the working voltage and the deposited charge. Within this voltage range, the safety threshold of the aluminum shielding layer needs to reach 4-5 mm. In summary, under high working voltage, the grounding area of the sample can be increased, and the appropriate working conditions can be selected to determine the optimal shielding thickness that can suppress dielectric electrostatic discharge.

This paper investigates the bridging behavior of fiber particles in insulating oil under the background of flow-electric coupled field, which is of great significance for explaining the micro-discharge and the deterioration of overall electrical property of insulating oil in transformer. Based on the observation experiments, a constructed oil circulation device and shooting system is used to study the bridging characteristics of fiber particle swarm in oil flow under DC electric field. The effects of electric field intensity, oil flow velocity and mass fraction of particles in oil on the bridging process are analyzed in detail, and the changes of conduction current between electrodes under different conditions are recorded. The results show that the bridging behavior of fiber particle swarm is the result of the combined action of flow field and electric field. The forces provided by electric field on the fiber particles cause them to aggregate and bridge between electrodes, and with the increase of field intensity, the bridging speed increases significantly. The influence of flow velocity is more complicated, and it has different effects on the bridging process of particles under low and high field intensity. The mass fraction of fiber particles in oil is negatively correlated with the difficulty of bridging between electrodes. Finally, the bridging mechanism is explained from the perspective of the forces on particles and electric field distortion, and the variation characteristics of conduction current between electrodes are analyzed.

When using high-voltage transmission lines for energy transmission in loess hilly regions, local extreme wind fields such as turbulence and high-speed cyclones occur from time to time, which can cause many kinds of mechanical and electrical failures, seriously affecting the reliable and stable energy transmission of the power grid. The existing research focuses on the wind field simulation of ideal micro-terrain and actual terrain with mostly single micro-terrain characteristics. Model boundary constraints and the influence of constrained boundaries are the main problems that need to be solved to accurately model and simulate complex flow fields. In this paper, a flow field simulation method based on circular boundary constraints is carried out. During the study, the influence of the model boundary and the selection conditions of the modeling range are systematically analyzed. It is more suitable to make sure that the air domain is 4 times higher than the height of the hill undulations, in addition to ensuring that there should be a minimum of 400 m between the study region and the boundary. Then, an actual terrain model of a power grid line in Shanxi is established, through the method proposed in this paper, the wind speed at the location of the transmission tower line under different wind directions is analyzed, and it is found thatwhen the incidence direction is 45 degrees north by east the wind speed is the highest. The findings demonstrate that the circular boundary model has the advantage of more easily adjusting the wind incidence direction, in addition to theoretically reducing the errors caused by traditional models in boundary processing. It can accurately obtain the distribution characteristics of the flow field affected by the terrain, and quickly screen out the extreme working conditions that are most harmful to the transmission lines in the actual transmission line for energy transmission in complex loess hilly regions.

Superhydrophobic surfaces have attracted much interest for its potential applications. In this study, the superhydrophobic aluminum surfaces were fabricated by method of chemical etching. Aluminum surfaces were firstly chemically etched by hydrochloric acid, and modified with stearic acid. The relationship between the etching time and the surface hydrophobicity was investigated. The contact angle and the sliding angle were tested, the results showed that with increasing etching time, the contact angle experienced a rise and then decrease, while the sliding angle dropped first and then started to climb. A maximum value of 152 degrees for the contact angle and a minimum value of 3 degrees for the sliding angle were obtained with etching time of 1 minute. The results indicated an ideal superhydrophobic property of the aluminum surfaces.