Understanding the mechanism of coalescence-induced self-propelled jumping behavior provides distinct insights in designing and optimizing functional coatings with self-cleaning and anti-icing properties.However,to dat...Understanding the mechanism of coalescence-induced self-propelled jumping behavior provides distinct insights in designing and optimizing functional coatings with self-cleaning and anti-icing properties.However,to date self-propelled jumping phenomenon has only been observed and studied on superhydrophobic surfaces,other than those hydrophobic surfaces with weaker but fairish water-repellency,for instance,vulcanized silicon rubber(RTV) coatings.In this work,from the perspective of thermodynamic-based energy balance aspect,the reason that self-propelled jumping phenomenon does not happen on RTV coatings is studied.The apparent contact angles of droplets on RTV coatings can be less than the theoretical critical values therefore cannot promise energy surplus for the coalesced droplets onside.Besides,on RTV and superhydrophobic surfaces,the droplet-size dependent variation characteristics of the energy leftover from the coalescence process are opposite.For the droplets coalescing on RTV coatings,the magnitudes of energy dissipations are more sensitive to the increase in droplet size,compared to that of released surface energy.While for superhydrophobic coatings,the energy generated during the coalescence process can be more sensitive than the dissipations to the change in droplet size.展开更多
Accurate conditions monitoring and early wrong action warnings of relay protection in the Smart Substation is the basic guarantee to realize the normal operation of primary and secondary system of the power grid.At pr...Accurate conditions monitoring and early wrong action warnings of relay protection in the Smart Substation is the basic guarantee to realize the normal operation of primary and secondary system of the power grid.At present,the traditional operation and maintenance monitoring methods of relay protections have poor timeliness,while some automatic monitoring methods have insufficient early warning performance,and lack the online action deduction function independent of the actual device.In this paper,a design method of integrated action deduction system including protection logic reasoning and software and hardware operation condition is proposed.The system can receive real-time operation information of protection online,simulate different types of faults,and output the recording information of sub modules belongs to the action deduction system.It can realize the online monitoring of device faults such as deducing the correctness of setting values at a certain time in the future,giving the wrong action warnings and predicting the probability of them as well,which effectively improves the operation and maintenance efficiency of the secondary system in the intelligent substation.展开更多
As the widely implemented electrode material,graphite has the characteristic of sublimation by the thermal shock of the switching arc,and the produced carbon vapor is easy to condense into carbon powders and deposit i...As the widely implemented electrode material,graphite has the characteristic of sublimation by the thermal shock of the switching arc,and the produced carbon vapor is easy to condense into carbon powders and deposit in the switch.The impact of the type of dilution gas in a mixture of20%oxygen and 80%dilution gas on the sublimation and oxidation characteristics of the graphite electrode is investigated.It is found that when nitrogen dilution gas was replaced by argon,the heat flux to the electrodes decreased,which led to a 63%reduction of graphite sublimation.At the same time,the cooling rate of the arc was slower in argon,which promotes oxidation of the carbon vapor.The residual solid carbon can be reduced by 70%–85%by using argon as the dilution gas.Consequently,it is demonstrated that the stability and working life of the switch could be increased by appropriate selection of the dilution gas.展开更多
In recent years,more and more high-voltage overhead transmission lines were built passing through the karst regions in southwestern China.This type of special landform seems to have an adverse effect on the aging of t...In recent years,more and more high-voltage overhead transmission lines were built passing through the karst regions in southwestern China.This type of special landform seems to have an adverse effect on the aging of the sheds of the line suspension composite insulators,which may lead to unexpected flashover and line tripping.In order to find out the particularity of the aging characteristics of insulators operating in the karst regions,samples in operation were selected from both the karst regions and the flatlands.Hydrophobicity,amount of surface contamination,and contaminant composition of the sheds were studied,then a comparison of performance between the two was made,and the possible influencing factors that cause such differences were discussed.The results show that the overall aging of the sheds of the composite insulators operating at the karst regions is more aggravated,which is caused by the combined influence of factors including the special topography,climate,and pollution in the area.The strong wind crossing the col will bring about the mutual scraping on the edges and stress concentration at the root of the sheds,leaving scratches and root cracks;the infiltration from these rupture of acid liquid,if any,will accelerate the aging and corroding of the internal silicone rubber material;moreover,the carbonates enriched on the surface of the sheds will gradually transform into more corrosive sulfates in an acidic environment,leading to further deterioration and chalking of the sheds of the insulators.The research work in this paper can provide guidance for the current operation and maintenance of composite insulators in the karst areas,as well as having important reference values for the layout design and insulation configuration of transmission lines to be built across karst landforms in the future.展开更多
Biomimetic superhydrophobic(SH)coatings have emerged as a promising alternative to traditional room temperature vulcanizing(RTV)silicone rubber coatings for improving the flashover strength of insulators.However,organ...Biomimetic superhydrophobic(SH)coatings have emerged as a promising alternative to traditional room temperature vulcanizing(RTV)silicone rubber coatings for improving the flashover strength of insulators.However,organic contamination occurs in outdoor applications and thus a superamphiphobic(SAP)surface is more desirable but not yet reported for improving flashover performance.Herein,we developed a novel anti-flashover technique by fabricating robust SAP coating with unique gradient and micro-nanoscale hierarchical architecture.The SAP coating was fabricated by sequentially spray-depositing a resin-based primer and a silica-based topcoat on substrates(i.e.,glass slides and insulators).The primer not only functions as an adhesive offering strong adhesion to the substrate but also offers a micromastoid-like structure facilitating the subsequent formation of hierarchical micro-nanostructure.The appropriate spraying pressure leads to a diffusion of the fluorocarbon-modified silica nanoparticles into the primer to form a unique gradient structure,by analogy to inserting bullets into a wood.These features render the SAP coating excellent robustness with strong abrasive resistance,excellent ultraviolet(UV)resistance,and excellent chemical and thermal stability.Pollution flashover property of the SAP coating was explored and compared with that of SH and RTV specimens,from which a novel organic-contamination model to evaluate the flashover performance was proposed.The coated SAP glass insulator demonstrated 42.9%pollution flashover voltage improvement than RTV-coated insulator.These stated unique features reveal the convincing potential of the present SAP coatings to be applied for not only outdoor transmission line insulators for antiflashover but also other fields for self-cleaning,anti-fouling,and anti-icing.展开更多
Insulators on high-voltage Uansmission lines are almost the only man-made structures on the Earth's surface intended for long-term operation under strong electric fields. After samples of natural contaminant parti...Insulators on high-voltage Uansmission lines are almost the only man-made structures on the Earth's surface intended for long-term operation under strong electric fields. After samples of natural contaminant particles were collected from insulator surfaces in China, it was found that the particle diameter distribution (PDD) was mainly concentrated in the 5-50 μm range. To analyze the statistical characteristics of these particles, this work studies the physical processes of particle collision and adhesion using the theories of hydrodynamics and collision dynamics. The physical model considers coupling of the fluid field and the electric field, introduces an adhesion criterion, and establishes a particle and surface collision model. The effects of relative humidity, wind speed, aerodynamic shape, electric field type, and electric field strength on particle adhesion were analyzed. The results show that the relative humidity and wind speed have very significant effects and the influences of the electric field type and the electric field strength are obvious, but the in fluence of the aerodynamic shape is relatively weak. The simulation results support the statistical characteristics determined in this work. The physical model established here provides reference values for study of the adhesion characteristics of particles on surfaces under electric fields.展开更多
文摘Understanding the mechanism of coalescence-induced self-propelled jumping behavior provides distinct insights in designing and optimizing functional coatings with self-cleaning and anti-icing properties.However,to date self-propelled jumping phenomenon has only been observed and studied on superhydrophobic surfaces,other than those hydrophobic surfaces with weaker but fairish water-repellency,for instance,vulcanized silicon rubber(RTV) coatings.In this work,from the perspective of thermodynamic-based energy balance aspect,the reason that self-propelled jumping phenomenon does not happen on RTV coatings is studied.The apparent contact angles of droplets on RTV coatings can be less than the theoretical critical values therefore cannot promise energy surplus for the coalesced droplets onside.Besides,on RTV and superhydrophobic surfaces,the droplet-size dependent variation characteristics of the energy leftover from the coalescence process are opposite.For the droplets coalescing on RTV coatings,the magnitudes of energy dissipations are more sensitive to the increase in droplet size,compared to that of released surface energy.While for superhydrophobic coatings,the energy generated during the coalescence process can be more sensitive than the dissipations to the change in droplet size.
基金supported by the Science and Technology Program of State Grid Corporation of China(No.kj2020–056).
文摘Accurate conditions monitoring and early wrong action warnings of relay protection in the Smart Substation is the basic guarantee to realize the normal operation of primary and secondary system of the power grid.At present,the traditional operation and maintenance monitoring methods of relay protections have poor timeliness,while some automatic monitoring methods have insufficient early warning performance,and lack the online action deduction function independent of the actual device.In this paper,a design method of integrated action deduction system including protection logic reasoning and software and hardware operation condition is proposed.The system can receive real-time operation information of protection online,simulate different types of faults,and output the recording information of sub modules belongs to the action deduction system.It can realize the online monitoring of device faults such as deducing the correctness of setting values at a certain time in the future,giving the wrong action warnings and predicting the probability of them as well,which effectively improves the operation and maintenance efficiency of the secondary system in the intelligent substation.
基金supported by National Natural Science Foundation of China(Nos.51777082 and 52077091)Chinese Scholarship Council(No.201906160101)。
文摘As the widely implemented electrode material,graphite has the characteristic of sublimation by the thermal shock of the switching arc,and the produced carbon vapor is easy to condense into carbon powders and deposit in the switch.The impact of the type of dilution gas in a mixture of20%oxygen and 80%dilution gas on the sublimation and oxidation characteristics of the graphite electrode is investigated.It is found that when nitrogen dilution gas was replaced by argon,the heat flux to the electrodes decreased,which led to a 63%reduction of graphite sublimation.At the same time,the cooling rate of the arc was slower in argon,which promotes oxidation of the carbon vapor.The residual solid carbon can be reduced by 70%–85%by using argon as the dilution gas.Consequently,it is demonstrated that the stability and working life of the switch could be increased by appropriate selection of the dilution gas.
基金supported by Science and Technology Project of Southern Power Grid EHV Transmission Company of China(010700KK52190003).
文摘In recent years,more and more high-voltage overhead transmission lines were built passing through the karst regions in southwestern China.This type of special landform seems to have an adverse effect on the aging of the sheds of the line suspension composite insulators,which may lead to unexpected flashover and line tripping.In order to find out the particularity of the aging characteristics of insulators operating in the karst regions,samples in operation were selected from both the karst regions and the flatlands.Hydrophobicity,amount of surface contamination,and contaminant composition of the sheds were studied,then a comparison of performance between the two was made,and the possible influencing factors that cause such differences were discussed.The results show that the overall aging of the sheds of the composite insulators operating at the karst regions is more aggravated,which is caused by the combined influence of factors including the special topography,climate,and pollution in the area.The strong wind crossing the col will bring about the mutual scraping on the edges and stress concentration at the root of the sheds,leaving scratches and root cracks;the infiltration from these rupture of acid liquid,if any,will accelerate the aging and corroding of the internal silicone rubber material;moreover,the carbonates enriched on the surface of the sheds will gradually transform into more corrosive sulfates in an acidic environment,leading to further deterioration and chalking of the sheds of the insulators.The research work in this paper can provide guidance for the current operation and maintenance of composite insulators in the karst areas,as well as having important reference values for the layout design and insulation configuration of transmission lines to be built across karst landforms in the future.
基金the project“Synthesis and Application of Superhydrophobic Self-cleaning Materials for Electric Engineering”(No.6111901321)Overseas Expertise Introduction Project(111 project)for Discipline Innovation of China(No.B18038)the State Key Laboratory of Silicate Materials for Architectures(Wuhan University of Technology)Open Foundation(No.SYSJJ2021-02).
文摘Biomimetic superhydrophobic(SH)coatings have emerged as a promising alternative to traditional room temperature vulcanizing(RTV)silicone rubber coatings for improving the flashover strength of insulators.However,organic contamination occurs in outdoor applications and thus a superamphiphobic(SAP)surface is more desirable but not yet reported for improving flashover performance.Herein,we developed a novel anti-flashover technique by fabricating robust SAP coating with unique gradient and micro-nanoscale hierarchical architecture.The SAP coating was fabricated by sequentially spray-depositing a resin-based primer and a silica-based topcoat on substrates(i.e.,glass slides and insulators).The primer not only functions as an adhesive offering strong adhesion to the substrate but also offers a micromastoid-like structure facilitating the subsequent formation of hierarchical micro-nanostructure.The appropriate spraying pressure leads to a diffusion of the fluorocarbon-modified silica nanoparticles into the primer to form a unique gradient structure,by analogy to inserting bullets into a wood.These features render the SAP coating excellent robustness with strong abrasive resistance,excellent ultraviolet(UV)resistance,and excellent chemical and thermal stability.Pollution flashover property of the SAP coating was explored and compared with that of SH and RTV specimens,from which a novel organic-contamination model to evaluate the flashover performance was proposed.The coated SAP glass insulator demonstrated 42.9%pollution flashover voltage improvement than RTV-coated insulator.These stated unique features reveal the convincing potential of the present SAP coatings to be applied for not only outdoor transmission line insulators for antiflashover but also other fields for self-cleaning,anti-fouling,and anti-icing.
基金the Science-Technology Program of the State Grid Corporation of China (grant No. 521700140004)and the National Natural Science Foundation of China (grant No. 51777082)and the Fundamental Research Funds for the Central Universities (grant No. 2016YXZD069).
文摘Insulators on high-voltage Uansmission lines are almost the only man-made structures on the Earth's surface intended for long-term operation under strong electric fields. After samples of natural contaminant particles were collected from insulator surfaces in China, it was found that the particle diameter distribution (PDD) was mainly concentrated in the 5-50 μm range. To analyze the statistical characteristics of these particles, this work studies the physical processes of particle collision and adhesion using the theories of hydrodynamics and collision dynamics. The physical model considers coupling of the fluid field and the electric field, introduces an adhesion criterion, and establishes a particle and surface collision model. The effects of relative humidity, wind speed, aerodynamic shape, electric field type, and electric field strength on particle adhesion were analyzed. The results show that the relative humidity and wind speed have very significant effects and the influences of the electric field type and the electric field strength are obvious, but the in fluence of the aerodynamic shape is relatively weak. The simulation results support the statistical characteristics determined in this work. The physical model established here provides reference values for study of the adhesion characteristics of particles on surfaces under electric fields.
