Dynamic physical characteristics of DC arc on arcing horn for HVDC grounding electrode line

The dynamic physical characteristics of a DC arc on an arcing horn for a high voltage direct current(HVDC)grounding electrode line are significantly different from those of the switching device arc,secondary arc,AC fault arc and pantograph-catenary arc.In this work,an experimental platform for the DC arc on the arcing horn was built,and mechanisms of the arc column short circuit and arc root movement were studied.This work further analyzes the characteristics and mechanisms of the arc motion when wind speed and direction,magnetic field and the expansion angle of the electrode are varied.Arc root movement is more likely to occur at the upper electrode.There is a competitive relationship between arc expansion and the transferring effect.The effect of wind on the arc column is greater than the effect on the arc root.The magnetic field has a significant driving effect on both the arc column and the arc root.The research results provide a comprehensive experimental basis for forther probing the method of DC arc suppression,and the improvement of the arcing horn.

钌基单原子和团簇催化剂在电催化反应中的竞争和协同效应

单原子和团簇催化剂在电催化领域,尤其是可持续能源存储和转化领域的重要性,得到越来越多地认可.单原子催化剂具有低金属负载和高原子利用效率的优点,但由于其表面自由能常常使得单个原子不稳定而发生聚集.团簇催化剂则因为其高原子利用率以及多样的活性位点,能够克服单原子催化剂在中间体吸附和活化等方面的局限性.钌基催化剂在电催化中有着十分重要的应用前景.然而,准确设计钌基单原子和团簇催化剂的几何和电子结构,并揭示它们之间的结构-性质关系,仍然面临着巨大的挑战.因此,我们对钌基催化剂进行了分类和比较(同源/异源),重点总结了钌基单原子和团簇在电催化领域的竞争和协同效应.近年来,钌基催化剂在析氢反应(HER)方面取得了显著进展,因此着重介绍钌基催化剂在HER中的应用,并涵盖了其他电催化反应、双功能反应(HER/OER、HER/HOR)和电化学有机反应.此外,本文还探讨了钌基单原子和团簇在HER过程中的催化机理.最后,我们指出了在复杂钌基催化剂的工业应用开发策略中所面临的挑战和前景.

Experimental study on dynamic response characteristics of isolated-span transmission lines after ice-shedding

The dynamic response characteristics,including maximum jump height and unbalanced tension,of isolated-span transmission lines after ice-shedding are investigated by means of experiments.A reduced-scale modelling method for ice-shedding from conductor lines is presented and verified with numerical simulations and full-scale test results in the literature.A parameter study on dynamic responses of isolated-span conductors under three ice-shedding scenarios,including whole span ice-shedding,partial ice-shedding and unzipping ice-shedding,is carried out by means of reduced-scale modelling tests.The effects of these parameters on the maximum jump height at typical positions and unbalanced tension in the tension tower are obtained.It is observed that the partial iceshedding scenario may be the worst situation for electrical insulation clearance rather than the whole span ice-shedding scenario.Moreover,the position of maximum jump height along the span of isolated-span transmission lines after ice-shedding could be at around 2/5 of span length,which is different from the conventional opinion that the position is at the midpoint.The results may provide a foundation for the defining of the insulation clearance for an isolated-span transmission line and the structure design of tension tower arms in an iced zone.

Systematic protective scheme for mega‐city power systems against stray currents caused by metro systems

In modern megacities,stray currents from metro systems intrude into multiple transformers'neutral points becoming a potential threat to the high‐capacity transformers.Neutral current anomalies are exacerbated in unprotected substations when we instal guards at single stations.This paper presents a system protection strategy for multiple substations affected by stray currents in modern megacities.The model,taking Shanghai as an example,includes the spatial distribution information of the urban electrical energy transmission structure,the power system,and the metro system.A Particle swarm algorithm is used to calculate the resistance values of the devices for each station.Further stability tests are performed to select the optimal protection solution.The results show that when protection is considered as a system,the protection runs well and the neutral current level remains below the unprotected level when the protection fails at a single station or multiple stations.

Self-cleaning of superhydrophobic nanostructured surfaces at low humidity enhanced by vertical electric field

Self-cleaning is the key factor that makes superhydrophobic nanostructured materials have wide applications.The self-cleaning effect,however,strongly depends on formations and movement of water droplets on superhydrophobic nanostructured surfaces,which is greatly restricted at low humidity(<7.6 g·kg^(-1)).Therefore,we propose a self-cleaning method at low humidity in which the pollution is electro-aggregated and driven in the electric field to achieve the aggregation and cleaning large areas.The cleaning efficiency of this method is much higher than that of water droplet roll-off,and will not produce"pollution bands".A simplified numerical model describing pollution movements is presented.Simulation results are consistent with experimental results.The proposed method realizes the self-cleaning of superhydrophobic nanostructured surfaces above dew point curve for the first time,which extends applications of superhydrophobic nanostructured materials in low humidity,and is expected to solve self-cleaning problems of outdoor objects in low humidity areas(<5.0 g·kg^(-1)).

Pollution morphology characteristics on a superhydrophobic surface and its pollution flashover voltage in DC electric field

To solve the pollution problem of insulators on ultra-high voltage DC transmission lines,superhydrophobic coatings were presented and their pollution deposit morphology and pollution flashover voltage in electric field were studied by an artificial pollution deposit system.The experimental results show that the pollution on the surface of super-hydrophobic coating is distributed in clusters,which inhibits the chain distribution on the surface of silicone rubber and improves the pollution flashover voltage.Secondly,the competition mechanism of the pollution flashover on the superhydrophobic coating surface was found.This competition mechanism can lead to the failure of the insulation performance of the superhydrophobic coating in severely polluted environments.Finally,a pollution flashover model of superhydrophobic coating is proposed to explain the competition mechanism,which is affected by pollution and the discrete droplets.The conclusions of this study can provide an experimental and theoretical basis for the application of the superhydrophobic coating in the field of UHV DC external insulation.

Method for detecting the pollution degree of naturally contaminated insulator based on hyperspectral characteristics

Insulator pollution degree detection is of great significance for preventing a flashover.Equivalent salt deposit density,leakage current,and surface pollution layer conductivity are commonly used to describe insulator pollution degree;however,all these parameters have limitations in field application and real‐time monitoring.Non‐contact detection methods,such as infrared thermal imaging and ultraviolet imaging,only image insulators in a specific band,which makes the extracted features limited.Hyperspectral technology is the new comprehensive image data technology based on imaging spectroscopy that has the advantages of multiband high resolution.Therefore,a method based on hyperspectral image and spectral characteristics is proposed to fully characterize natural pollution in-formation and accurately detect the pollution degree of insulators.The hyperspectral spectral line characteristics,image texture,and colour characteristic data of insulators were extracted and fused and then used to establish the pollution degree detection model on the basis of integrated learning classification algorithms.The results show that the model based on fusion data has an accuracy rate of 95.0%,which is more accurate than the model based on spectral line features only.Consequently,hyperspectral technology can realize the non‐contact detection of pollution degree and provide some guidance for cleaning the contamination of external insulation.

Universal precursors dispersed in Vaseline-octadecene gel for nanocrystal synthesis

A great variety of high-quality inorganic nanocrystals are synthesized solely in hydrocarbon solvents in both academic and industrial settings on a daily basis,which is largely complicated by lack of simple precursors containing inorganic element(s)yet soluble in the reaction solvents at ambient temperatures.Here,we introduce a new strategy for preparing the precursors,namely inorganic(or element-containing organic)molecules dispersed in hydrocarbon(Vaseline-octadecene)gel.This strategy not only greatly expands spectra of potential precursors and their concentration range,but also simplifies synthetic system,enables automated large-scale synthesis,and minimizes environmental concerns.