Numerical Simulation of Contamination Accumulation Characteristics of Composite Insulators in Salt Fog Environment

To investigate the fouling characteristics of the composite insulator surface under the salt fog environment,the FXBW-110/120-2 composite insulator was taken as the research object.Based on the field-induced charge mechanism,the multi-physical field coupling software COMSOL was used to numerically simulate the fouling characteristics,explored the calculation method of ESDD,and demonstrated its rationality.Based on this method,the pollution characteristics of the composite insulator under the pollution fog environment were studied,and the influence of wind speed,droplet size,and voltage type on the pollution characteristics of the composite insulator was analyzed.The results showed that:with the increase in wind speed,the amount of accumulated pollution of insulator increases in the range of droplet size,and the relationship between wind speed and accumulated pollution is approximately linear;at the same wind speed,the amount of accumulated pollution increases with the increase of droplet size under the action of DC voltage;when there is no voltage,the amount of dirt on the upper surface of the insulator is more than that on the lower surface,while it is the opposite under DC voltage.

Influence of materials’hygric properties on the hygrothermal performance of internal thermal insulation composite systems

Internal thermal insulation composite system(ITICS)can be an important measure for the energy-saving retrofitting of buildings.However,ITICS may cause harmful effects on the hygrothermal performance of building envelopes.This work investigated the influence of the materials’hygric properties on the hygrothermal perfor-mance of a typical ITICS in different climate conditions in China.Two base wall materials,the traditional concrete and a new type aerated concrete,were tested and compared for their hygric properties firstly.The influence of the hygroscopicity of exterior plasters,the permeability of insulation materials and the climate conditions were then analyzed with WUFI simulations.The hygrothermal performance was evaluated with consideration of the total water content(TWC)of the walls and the moisture flux strength,the relative humidity(RH)and the mould growth risk at the interface between the base wall and the insulation layer(B-I interface).The numerical analysis implies that the TWC of internal insulated walls depends mainly on the hygroscopicity of exterior plaster and the wind-driven rain intensity.The upper limits for the water absorption coefficient of exterior plasters used in Bei-jing,Shanghai and Fuzhou are 1e-9,1e-10,1e-10 m^(2)/s respectively.When such limits are guaranteed,a vapour tight system created by using insulation materials with a large vapour resistance factor or adding a vapour barrier can improve the hygrothermal performance of ITICS,especially for concrete walls in cold climate.

Fiber Bragg grating monitors for thermal and stress of the composite insulators in transmission lines

Running composite insulators are prone to failure due to their harsh surrounding work environment, which directly affects the safe operation of transmission lines. This paper puts forward the method of using fiber Bragg grating(FBG) as the monitors to parameters correlated with thermal and stress of the composite insulators in transmission lines at working status. Firstly, monitoring points are found out by the mechanical test on composite insulator samples. Secondly, based on the monitoring theory, this paper introduces the feasibility design frame of the composite insulator with FBG implanted in the rod and the online monitor system. At last, it describes applications of this monitor system in the field of transmission lines.

Aging Characteristics and Influencing Factors of the Sheds of Composite Insulators in Karst Regions of China

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.

Research on a Composite Biomass Insulation Material with Geopolymers as Binders and Forestry Waste as Fillers

A composite biomass insulation material,which uses geopolymers as adhesives and forestry waste as fillers,was proposed and experimentally tested.The orthogonal experimental method was adopted to analyze the optimum theoretical oxide molar ratios and the mass ratio of mixing water to binder(m_(w2)/m__(B))for preparing geopolymers.The influences of curing regimes(including one-stage and two-stage curing methods)and m_(w2)/m_(B) ratios of the insulation materials on mechanical,thermal,and hydraulic performances were also studied by experiment.The results indicated that the optimum combination scheme of preparing geopolymers was molar ratio x_(SiO_(2))/x_(Na_(2)O)=3.3,x_(SiO_(2))/x_(Al_(2)O_(3))=3.2 and m_(w2)/m_(B)=0.5 with the highest mechanical strength of 34.21 MPa.Besides,the best curing conditions of the composite material were the curing temperatures of 85°C and 70°C under the two-stage curing regime,which could achieve the low heat conductivity of 0.123 and 0.125 W/(m·K),and the high mechanical strength of 1.70 MPa and 1.71 MPa,respectively.The optimum m_(w2)/m_(B)ratios of the biomass material were 0.5 to 0.55 with heat conductivity of 0.114 to 0.125 W/(m·K).This novel composite insulation material has satisfying physical performances,which is helpful for achieving building energy conservation.

Dynamic performance and energy efficiency of reflective and insulative composite coating on building exterior wall

Reflective and insulative composite coatings are a new energy-saving material with high solar reflectance and extremely low thermal conductivity for buildings.The optimization and impact of high solar reflectance and low thermal conductivity on the insulating capacity of walls remain uncertain.This work investigates the dynamic thermal performance and energy efficiency of a reflective and insulative composite coating in regions with hot summer and warm winter.A simplified thermal resistance-heat capacitance model of an exterior building wall is established to predict thermal performance.The dynamic temperature and heat flow of the wall are predicted to reduce heat loss through the interior surface of the wall and compared to the conventional coating.The specific impact of the thermal conductivity and solar reflectance of the coating on the heat loss is further investigated to minimize heat loss of the wall.This research shows that the composite coating shows better performance on adjusting outdoor climate change than the other coating.Compared with cement,it reduces the maximum temperature of the exterior surface of the wall by 7.45°C,and the heat loss through the interior surface of the wall by 38%.The heat loss is reduced with the increase of solar reflectance and the reduction of thermal conductivity.The results can provide a useful reference and guidance for the application of reflective and insulative composite coating on building exterior wall to promote their energy-saving use on building envelopes.

Influence of Electrical Field Distortions Induced by Water Droplets on the Contamination Characteristics of an Insulator

When separated water droplets condense on the surface of a composite insulator,the electrical field on the insulator surface is distorted.In turn,such distortions change the trajectories of pollution particles.In this study,the COMSOL software is used to simulate such a process for the FXBW4-10/100 composite insulator with or without water droplets condensation under a 10 kV DC voltage.The influence of the wind speed and particles concentration on the contamination characteristics of the considered 110 kV insulator is analyzed.The results show that:1)in the presence of water droplets on the insulator surface,the ratio of electrical field force and gravity acting on the particles is large;2)the contamination on the insulator surface increases with the wind speed;3)when the wind speed is small,the relationship between the contamination amount and the pollution concentration is essentially linear.

Intelligent Breakage Assessment of Composite Insulators on Overhead Transmission Lines by Ellipse Detection Based on IRHT

With the development of unmanned aerial vehicle(UAV)technology,visible images are playing an important role in the maintenance of power systems.To achieve the shed breakage evaluation of composite insulators by UAV visible images,an intelligent fault assessment method is proposed.First,the composite insulators in visible light images are identified by Faster-RCNN.After image preprocessing,the image is enhanced and the noise is removed.Then,a canny operator is used to extract the edge of the sheds.An Improved Randomized Hough Transform(IRHT)is used to detect the ellipses in the edge image.The parameters of the detected ellipse,length of major axes and minor axes,center coordinates and deflection angle of major axes,are used to realize the segmentation of the composite insulator.Finally,the number of pixel points in the ellipse and the distance between the points and the ellipse boundary are used to judge whether there are breakage or cracks on the sheds.The area ratio of the breakage to the whole shed is calculated based on the number of pixel points inside the broken area.This method can be realized without a large amount of training dataset of the specific fault type and provides a technical basis for the online fault assessment of a composite insulator on overhead transmission lines.

Review on the Characteristics,Heating Sources and Evolutionary Processes of the Operating Composite Insulators with Abnormal Temperature Rise

This paper reviews the research progress on abnormal temperature rise(ATR)of composite insulators.The ATR of composite insulators can be divided into two types,point-form temperature rise(PFTR)and bar-form temperature rise(BFTR).The composite insulators with PFTR only show significant temperature rise at high relative humidity(RH)(>70%),and the temperature rise is located in the area that is 20 cm above the metal end-fitting.In a low humidity environment(<30%),there is little temperature rise(<1.0 K).The polarization loss on the surface of the silicone rubber housing under an AC electric field after moisture absorption is the main heating source.Corona discharge in high RH causes surface degradation of the silicone rubber.The composite insulators with BFTR shows significant temperature rise at both high(>70%)and low(<30%)RH.The temperature rise could reach more than 10◦C and the temperature rise area is wider,extending from the high-voltage end to several shed units at the lowvoltage side.And the glass fiber reinforced plastic(GRP)core in the composite insulator is found to be corroded.The heating energy is supplied by both conductance loss and polarization loss of the corroded GRP core.The decay-like degradation of the GRP core is caused by the combination of damp conditions,high electric field,discharge,mechanical load,et al.and may evolve into a decay-like fracture of the composite insulator.The preventive methods concerning quality control,structure optimization,material modification and operational strategy are presented.It is suggested that when PFTR is detected on the composite insulator,the inspection period of the insulator should be properly shortened.The composite insulator should be replaced as soon as the BFTR was detected.

Effect of Salty Fog on Flashover Characteristics of OCS Composite Insulators

To study the flashover characteristics of the fog water in saline-alkali areas for high-speed railway OSC insulators,the spatial distributions of both the potential and electric field of soiled insulators in the presence of salty fog are analyzed using COMSOL Multiphysics,a multi-physics coupling software.Furthermore,to analyze the effect of the contamination of insulators due to salty fog water,a saline solution is used for staining an insulator sample by using the solid coating method.In an artificial climate chamber,the salty fog environment is simulated,and the flashover voltage for different salty fog water conductivities and surface staining are obtained.The salt-density correction coefficient K is also proposed.It provides a strong basis for the selection of railway insulators in saline-alkali areas.The results show that the salty fog water changes the original surface equivalent salt density,ρESDD,by wetting the existing fouling layer on the surface of the insulator,so that the original surface contamination layer becomes equivalent to KρESDD;the smaller is the value ofρESDD of the insulator surface,the larger is the value of K;the surface of the same insulator is dirty,and as the concentration of salty fog-water increases,K also increases.

Organic thin film transistors with a SiO_2/SiN_x/SiO_2 composite insulator layer

We have investigated a SiO2/SiNx/SiO2composite insulation layer structured gate dielectric for an organic thin film transistor(OTFT) with the purpose of improving the performance of the SiO2gate insulator. The SiO2/SiNx/SiO2composite insulation layer was prepared by magnetron sputtering.Compared with the same thickness of a SiO2insulation layer device,the SiO2/SiNx/SiO2composite insulation layer is an effective method of fabricating OTFT with improved electric characteristics and decreased leakage current.Electrical parameters such as carrier mobility by field effect measurement have been calculated.The performances of different insulating layer devices have been studied,and the results demonstrate that when the insulation layer thickness increases,the off-state current decreases.

Time-domain Finite Element Method for Transient Electric Field and Transient Charge Density on Dielectric Interface

This paper is devoted to solving the transient electric field and transient charge density on the dielectric interface under the electroquasistatic(EQS)field conditions with high accuracy.The proposed method is suitable for both 2-D and 3-D applications.Firstly,the governing equations represented by scalar electric potential are discretized by the nodal finite element method(FEM)in space and the finite difference method in time.Secondly,the transient constrained electric field equation on the boundary(TCEFEB)is derived to calculate the normal component of the transient electric field intensities on the Dirichlet boundary and dielectric interface as well as the transient charge density on the dielectric interface.Finally,a 2-D numerical example is employed to demonstrate the validity of the proposed method.Furthermore,the comparisons of the numerical accuracy of the proposed method in this paper with the existing FEMs for electric field intensity and charge density on the dielectric interface are conducted.The results show that the numerical accuracy of the proposed method for calculating the normal component of transient electric field intensities on the Dirichlet boundary and dielectric interface as well as the transient charge density on the dielectric interface is close to that of nodal electric potential and an order of magnitude higher than those of existing FEMs.