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Abstract Unclean air discharge refers to the discharge phenomenon of a large number of polluting gases, droplets or solid particles floating in the air, which will cause insulation breakdown and safety accidents for the power transmission equipment that have been left outdoors for a long time. In order to investigate the effects of particle concentration, particle size and dielectric constant on DC breakdown characteristics of unclean air gap, a self‐made discharge chamber was designed in this study. The air was filtered and passed into the discharge chamber to remove the influence of impurities contained in the air on the experimental results. Then, solid particles with different concentration, particle size and particle dielectric constant were added to the discharge chamber to carry out the DC positive polarity breakdown characteristic experiment. The experimental results show that compared with dry clean air, the presence of solid particle increases the breakdown voltage of the gap, and the increase proportion of breakdown voltage is related to the particle concentration, particle size and particle dielectric constant. With the same particle type and particle size, the increase proportion of breakdown voltage increases with the higher concentration, which up to 10.49%. For further investigating, the fluid mechanics model was selected to simulate the process of streamer discharge in unclean air. The results show that compared with dry clean air, the presence of particles enhances the gap discharge ionisation process, but also enhances the adsorption of particles, and the latter has stronger effect than the former, thus increases the gap breakdown voltage. At the same time, the enhancement of adsorption effect increases the electric field intensity of the gap and speeds up the development process of streamer discharge.
Superhydrophobic surfaces have garnered significant attention in various industrial applications, such as photovoltaic power generation, anti-icing, and corrosion resistance, due to their exceptional water-repellent properties. However, the poor durability of conventional superhydrophobic coatings has severely impeded their practical implementation. To achieve the dual self-recovery of microscale and nanoscale surface structures and maintain low surface energy after damage to superhydrophobic coatings, thereby enhancing their durability, a rapidly self-healing superhydrophobic coating was developed using polydimethylsiloxane (PDMS) and n-nonadecane in this study. The coating surface demonstrated exceptional hydrophobic characteristics, as evidenced by a water contact angle (WCA) of 157.5° and a sliding angle (SA) of 4.2° achieved at optimized proportions. Through scanning electron microscopy, it was observed that the coating surface exhibited a rough structure at both the microscale and nanoscale. The stability test results showed that the WCA only decreases by 5.7° and the SA only increases by 3.6° after 100 instances of external friction. The stability test results demonstrated that the superhydrophobic coating maintains excellent hydrophobicity under mechanical external forces and in acidic and alkaline environments. The results of the self-healing capability test showed that the WCA rebounded to 151.5° and 149.5° after we subjected the samples to 20 MPa of vertical pressure damage and chloroform exposure for 4 h, respectively. The coating regained a robust hydrophobic state even after experiencing repeated mechanical and chemical damage. The above results indicate that the resulting coating demonstrates outstanding durability, including high resistance to friction, stability against acids and alkalis, and the ability to self-recover hydrophobicity after repeated damage.
Wind turbines at high altitudes suffer icing harm frequently in winter, and the aerodynamic profile will be destroyed which leads to output power loss. Studying the aerodynamic parameters could provide references in icing prediction or anti-icing. 3D CFD simulation is a common method to solve these issues, but it consumes lots of computational resources and time. In this paper, a more simpler calculation model of aerodynamic parameters for iced wind turbine, which combining 2D CFD simulation method and blade element momentum, is proposed. The accuracy of this model is verified by comparing the calculated and measuring output power results. According to this model, axial inducing factor a, tangential inducing factor b, tangential force P N and normal force P T are calculated under different wind velocity as well. The results show that the max factor a appears near rotor tip while the max factor b appears near rotor root. Furthermore, with the increasing of wind velocity, P N and P T show an increasing trend. By comparing the normal force on blade under icing and clean condition, results show that, with wind velocity increasing, the difference of normal force will get larger and the max difference appears near the rotor tip.
Wind power has strong volatility and randomness. In the ice season, wind power is more susceptible to the climatic conditions, which is difficult to predict, and has an impact on grid scheduling. For this problem, a wind power prediction method based on wind turbine operating state and deep learning. This method takes the historical meteorological data and wind turbine power as input, and establishes a wind turbine operation state prediction model through a fully connected neural network to realize wind turbine operation state prediction. The CNN-BiLSTM model is used to predict the wind power without the ice, and then convert the power according to the running status of the turbine to forecasting the electrical power of the wind during the ice. The experimental findings indicate that the proposed model has good prediction performance in the ice season and verify its accuracy by comparing with the traditional method.
The shed configuration has an obvious effect on flashover performance of ice-covered composite insulators. Based on the flashover arc path, a "multi-arc, multi-ice-layer" mathematical model is proposed to predict AC flashover voltages of ice-covered composite insulators with different shed configurations during the melting period. The model takes into account two different arc paths across the tip of each un-bridge icicle. Moreover, the arc across the air gap is distinguished from the arc on the ice surface, and the residual ice layer resistance is divided into icicle resistance, arc root resistance and shed surface ice resistance. In order to verify this model, four kinds of 220 kV composite insulators with different shed configurations are tested under different icing conditions. The theoretical results from the model are found to be in good agreement with the experimental results.
Effects of vertical magnetic field on the breakdown process of the nanosecond pulse discharge in atmospheric air are studied via two-dimensional particle-in-cell/Monte Carlo collision simulations. The numerical model is chosen and defined reasonably, with reference to experimental situations and literature reports. It is shown that when the applied magnetic field is strong enough, the evolutionary characteristics of the ionization channel are greatly affected due to the Lorentz force on charged particles. The impact is manifested macroscopically by the slowing down of the ionization channel evolution speed, the ionization channel shift, and the improvement of the discharge uniformity. At the microscopic level, the impact is mainly reflected in the regulation of the highest-energy electrons and the regulation of the overall electron energy distribution. That is, the adoption of a strong vertical magnetic field is capable of suppressing the generation of energetic electrons. The authors' results explicitly demonstrate the regulation of vertical magnetic field on the breakdown process of the nanosecond pulse discharge, which provides more comprehensive knowledge for the atmospheric air gap nanosecond pulse discharge physics and the theoretical basis for application design.
Here we report an ultra-effective and reliable pathway to reduce GO into graphene by an about 4 seconds flame-assisted microwave process. A holey graphene with a C/O atom ratio of 31.1, a pore volume of 6.0 cm3 g-1, and a specific surface area of 1050.0 m2 g-1 was synthesized.
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