Porcelain insulator has been slowly replaced by composite insulator in power grid nowadays. However, flashover fault still occurs on this insulator type. Under certain conditions, partial discharges may occur on the insulator and lead to a complete flashover. The flashover can cause the breakdown and damage the whole power system. Therefore, this paper reports on the flashover voltage of 11kV composite insulator under different conditions. They are pollution methods, insulator surface condition, water content, operating orientations and the ambient temperature. It was found that the flashover voltage can be improved by using 0o operating orientation angle of the insulator, at lower temperature, dry condition, less insulator surface roughness and no pollution on the insulator. Therefore, a better understanding of flashover voltage under different pollution conditions may be attained from this work.

Flashover voltage of insulator string under various conditions

Self—aggregation of vapor—liquid phase transition

Because of superior anti-pollution flashover property,room temperature vulcanized silicone rubber coating(RTV coating) is widely applied in Chinese power system.Based on the RTV coated insulators energized for many years,the anti-pollution flashover abilities were studied in various hydrophobic states via pollution test.Furthermore,based on the hydrophobicity distribution state of various site RTV coated insulators,hydrophobic insulators with combined interface were created to simulate the extreme distribution state of hydrophobicity.Then,the ability of hydrophobicity on different position to prevent pollution flashover are investigated via the characters of the leakage currents during the long-term voltage withstand pollution test.Experimental results show that,the hydrophobic states under the surface of the insulators play an important role in increasing or maintaining the anti-pollution flashover abilities.In addition,both the hydrophobic pollution layer covered on the whole insulator and the difference of wetting process under and below the surface also greatly affect the anti-pollution flashover voltage of RTV coated insulators.Thereby,a new discrimination method is recommended to inspect and judge the hydrophobicity of insulators,primarily judging by the hydrophobic state of under surface and secondarily by the hydrophobic state of upper surface being.

Analysis on Effect of Hydrophobicity on Anti-pollution Flashover Performance of Line Insulators

To improve accuracy of calculating the static contact angle of hydrophilic materials,we proposed a static contact angle algorithm considering globule volume and hydrophobicity.The globule edge curve was generated by the Young-Laplace equation,in the meantime,noise was superimposed to the curve to simulate the error of edge extraction,thereby,we studied the influences of the globule volume and contact angle on circle fitting algorithm and ellipse fitting algorithm.When the contact angle is not more than 90°,the globule volume less than 200μL,and contact line shorter than 1cm,we studied the influence of noise content on accuracy of the two algorithms.The results indicate that,the influence of noise on the ellipse fitting algorithm is more remarkable than that on the circle fitting algorithm,and the larger contact angle,the smaller influence.The error of the circle fitting algorithm will increase obviously with the increase of the globule volume,and the ellipse fitting algorithm will increase slightly.If the contact angle is less than 15°,the circle fitting algorithm should be selected to calculate the contact angle.If the contact angle is larger than 15°and less than 70°,in the meantime,the globule volume is less than 7μL,the circle fitting algorithm should be selected.If the contact angle is larger than 15°and less than 70°,in the meantime,the globule volume is larger than 7μL,the ellipse fitting algorithm should be selected.If the contact angle is larger than 70°and less than 90°,the ellipse fitting algorithm should be selected.Finally,the proposed contact angle algorithm was used to calculate the static contact angle of silicone rubber samples with different hydrophobicities,and the conclusion was verified by the experiment.If the silicone rubber material is hydrophilic,the accuracy of the static contact angle measurement can be improved by using the proposed method.

Static Contact Angle Algorithm of Hydrophilicity and Its Application in Silicone Rubber Hydrophobicity Detection

In order to investigate the relationship between the surface trap and insulation performance of polymers.The theory of isothermal currents proposed by J.G.Simmson etc in 70s last century was introduced in this paper and a set up of measurement device was designed to measure the trapping parameters of the surface layer of polymers.3 kinds of polymer material films were used.The needle-plane corona discharge was employed to charge the samples.The upper side of each sample was subjected to a dc corona discharge in atmosphere,and the other side was grounded.The applied voltage was ±4 kV and the charging time was set as 2 min.After charging,all needle electrodes were taken away,and the two sides of the sample were short-circuited for 1 minute to remove the free charges.Then the surface potential of samples was measured without contacting a surface potential meter(S2001A,Kawaguchi),and the surface trapping parameters could be calculated by the theory of isothermal currents.The electrons and holes traps shape of LDPE and PTFE was similar but not similar to PP.Results show that density of electrons and holes traps and energy distribution are related with the macromolecular chain structure,the different atom attached to the main chain affects the traps distribution heavily.

Analysis of Surface Trapping Parameters of Solid Insulation Dielectrics

Pretreatment needs to be done before measuring the hydrophobicity of the composite insulators. However, the necessity of such pretreatment is questionable for operating composite insulators. Therefore, surface roughness of light pollution level, heavily pollution level, chalking and the impact of surface roughness on hydrophobicity characteristic (HC) was investigated in this paper. The paper does the research on the result indicated the surface roughness is one of main factor about the pretreatment effect on HC level and static contact angle. The pretreatment effect on HC level and static contact angle seemed to be very obvious and the percentage of static contact angle changed up to 15.3%, as the surface roughness was varied. The Ra and RSM of different pollution level shed percentage change up to 130% and 269%. While Ra and RSM of high surface roughness degree reach up to 3.242μm and 400μm, the hydrophobicity on the composite insulators lost permanent. The surface roughness can lead the water drop to two kinds of states transitions and it can make sample static contact Angle changed up to 31% within 10 minutes, which will also cause the different results of two measurement methods. Surface roughness of composite insulators was suggested as the added parameter in hydrophobicity tests.

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Surface Roughness Effect on the Hydrophobicity Characteristic of Operating Composite Insulators

ABSTRACT In this study, micro Coix lacryma-jobi L. vertical flow constructed wetlands with 0, 10 and 30 mg/L Cr6+ (in the form of K2Cr7O2) in the water sources were constructed to study the purification efficiency of chromium-contaminated wastewater, bacterial community diversity, chromium chemical speciation distribution and other indicators. The results showed that the constructed wetlands had high purification efficiency for chromium-contaminated wastewater. The removal rate of Cr6+ reached 99.61% and 95.45% in 10 and 30 mg/L Cr6+ treatment. The bacterial diversity index was unaffected by Cr6+ treatment; however, the bacterial richness index declined dramatically as Cr6+ treatment concentration increased. The bacterial community structure was influenced by the substrates pH, moisture content, organic matter and total chromium content. The abundance of Burkholderiaceae (uncultured) and Saccharimonadales (uncultured) were positively correlated with non-residual chromium content. The results contributed to understand the effect of chromium on bacterial community structure by considering the chromium chemical speciation.

https://www.tandfonline.com/doi/pdf/10.1080/26395940.2022.2128427?needAccess=true

Qian-yu Wang

Papers

Surface Roughness Effect on the Hydrophobicity Characteristic of Operating Composite Insulators

Effects of Cr6+ stress on chromium chemical speciation distribution and bacterial community structure in the Coix lacryma-jobi L. constructed wetlands