Jianlin Hu

DC flashover performance of insulator string with fan-shaped non-uniform pollution

Under continuous wind of single direction, the leeward area of insulator string may be polluted more seriously than windward area, making the pollution layer distributes like a fan-shape. In this paper, dc pollution flashover tests of 7-unit XP-70 insulator string with fan-shaped non-uniform pollution were carried out. Then the influence of fan-shaped non-uniform pollution on flashover voltage, flashover process, leeward side surface layer conductivity and surface pollution layer resistance were discussed. Research results indicate that, the ratio W/L of windward to leeward side salt deposit density (SDD) affects the dc flashover performance of insulator string. A reduction in W/L from 1/1 to 1/15 would give a decrease of 28% in flashover strength. Flashover voltage may also decrease when the occupation ratio (T) of leeward side increases from 10% to 30%. Under fan-shaped non-uniform pollution, U50 can still be expressed by a negative exponential function of SDD, and the effect of fan-shaped non-uniform pollution on U50-SDD relationship may mainly lie in changing the proportionality coefficient a rather than the exponent n; discharge path was restricted along the leeward side, which may make the air-gap arc easily formed and benefit the flashover process.

Electrical performance of 330-kV composite insulators with different shed configurations under icing conditions

Composite insulators have been widely used in the electric power utilities worldwide because of their excellent anti-contamination performance. However, because of their compact shed configurations, the electrical performance of fully ice-bridged composite insulators is inferior to that of the porcelain and glass insulators at the same voltage level. As shown in previous studies, shed configuration influences the electrical performance of iced composite insulators. In order to improve the electrical performance of composite insulators under icing conditions, five types of 330-kV composite insulators with different number of big sheds were used to compare their V50 withstand voltage performances. The experiments were carried out in the multifunction climate chamber in Chongqing University. The test results show that the V50 withstand voltage can be increased by adding big sheds. To obtain the best performance, the shed spacing of big sheds should be long enough to avoid icicle bridging. The test results also show that there is no guarantee that the electrical performance of composite insulators can be increased when the corona rings are present under heavy icing condition. When corona rings are needed, their dimension and that of the shed configuration should be designed with care.

Predictive Model for Equivalent Ice Thickness Load on Overhead Transmission Lines Based on Measured Insulator String Deviations

Transmission-line icing presents a serious threat to the safe operation of power systems. Therefore, the icing condition of overhead transmission lines must be accurately calculated for online monitoring and prewarning systems. Based on the icing data obtained at Xuefeng Mountain Natural Icing Stations (XMNIS), the cross-sectional shape of glaze icing on conductors was studied, and the correction coefficient of the actual nonuniform ice was proposed to provide an accurate and convenient method for field icing measurement. In addition, by analyzing the characteristics of the tension and tilt of the insulator string at the iced tangent tower, a new mechanical calculation model considering the ice and wind loads was established. One-month field observations and experiments were conducted in XMNIS, and it is shown that the calculation results have good agreement with experiment results, which suggests that the model can be used for ice thickness calculation and online monitoring on transmission lines.

Fabrication of Super-Hydrophobic Surfaces with Long-Term Stability

A novel approach was proposed to fabricate super-hydrophobic surfaces by depositing aggregates of fumed silica modified with hydroxy-terminated poly-dimethylsioxane and γ-aminopropyltriethoxysilane on surfaces of glass plates. The glass plates were treated with 2,3-epoxy propoxy propyltrimethoxysilicane based on an epoxy-amine system in advance. Aggregates of fumed silica were found to be chemically bonded to the treated glass surfaces and a surface possessing dual micron- and nanoscale hierarchical structures was observed on the super-hydrophobic surfaces. The laboratory testing results showed that the obtained surfaces possessed long-term super-hydrophobicity in air and maintained its super-hydrophobicity over a wide pH range.

Study on the DC Flashover Performance of Various Types of Insulators With Fan-Shaped Nonuniform Pollution

In areas with heavy dust or continuous wind in a single direction, fan-shaped nonuniform contamination at the windward and leeward side of the insulator string may affect flashover performance. In this paper, dc pollution flashover tests of insulators under fan-shaped nonuniform pollution were presented, and a comparison of flashover performance among 7-unit suspension insulator strings with four different disk profiles was made. Then, the influence of fan-shaped nonuniform pollution on flashover voltage, arc propagation, and critical leakage distance were investigated. Research results indicate that the insulators with different types were influenced variously on their flashover stress, utilization rate of creepage distance, and critical leakage distance by fan-shaped nonuniform pollution. A reduction in the ratio W/L of windward to leeward side salt deposit density (SDD) from 1/1 to 1/15 gave a median 35% ± 4% decrease in flashover strength. The extrapolation of results for the seven-unit strings suggests that some increment in shed space or structure height of the insulator can be preferable in dc transmission lines where there is fan-shaped nonuniform pollution accumulating at the windward and leeward side of the insulator string.

Icing performances of super-hydrophobic PDMS/Nano-silica hybrid coating on insulators

This paper presented a novel polydimethylsiloxane /nano-silica (PDMS/nano-silica) hybrid super-hydrophobic coating for anti-icing on insulators. Average water contact angle on the super-hydrophobic PDMS/nano-silica hybrid coating reached 1610. The super-hydrophobic PDMS/nano-silica hybrid coating had a rough surface with micro/nanometer dual-size structure. Icing experiment was carried out to investigate the anti-icing properties of the super-hydrophobic coating on insulator strings. AC icing flashover voltages of the two types of insulator strings were investigated. Results showed that the super-hydrophobic PDMS/nano-silica hybrid super-hydrophobic coating excellently restrained the icing on insulator strings. The AC flashover voltage of the ice coated insulator string with the super-hydrophobic PDMS/nano-silica hybrid coating was 100 kV which was higher than that of the ice coated insulator string with RTV silicone rubber coating.

Shed Configuration Optimization for Ice-Covered Extra High Voltage Composite Insulators

Abstract The electrical performance of composite insulators with adhered ice is less than that of porcelain or glass insulator strings, which is mainly caused by the shed configuration differences. In this paper, the shed configuration optimization for ice-covered Extra High Voltage (EHV) composite insulators is discussed in order to improve the electrical performance of ice-covered composite insulators. The effects of the position and length of the air gaps on the electric field distribution of ice-covered composite insulators are investigated and analyzed based on the electric field calculation model. The basic optimization principles of the shed configuration for ice-covered composite insulators are based on the electric field calculation results. Moreover, the artificial icing flashover tests on the ice-covered composite insulators with different shed configurations were carried out in artificial climate chamber, and the flashover path was recorded by a high speed camera. According to the flashover voltage and the flashover path of composite insulators with different shed configurations, it can be concluded that the composite insulators with large shed spacing and various shed diameters have better electrical performance and can be used in the transmission lines across the icing area.

Artificial icing and AC flashover tests on glass insulators with silicone acrylate resin hydrophobic coatings

Droplets on hydrophobic coating surfaces tend to roll off, which can reduce water volume for icing, help relieve the icing degree of insulators, and improve the electrical performance of iced insulators. Hydrophobic coating is considered as a potentially effective anti-icing method for insulators. Artificial icing and flashover tests for LXP-70 insulator strings coated with four types of silicone acrylate resin (SAR) hydrophobic coatings were conducted in an artificial climate chamber. Bare insulator strings were arranged as the control group. Ice morphology, ice density, growth of ice weight, and AC flashover voltage among different insulator strings were investigated under non-energized and energized conditions. The effects of different SAR coatings on icing performance mentioned above and AC flashover voltage were discussed. Test results indicate that the hydrophobic features of coatings significantly affected the morphology of ice layers of glass insulators with SAR coatings, that is, the stronger the hydrophobicity of the coatings was, the more granular the ice layer became. Ice density was lower on the insulator surface with SAR coatings than that on the insulator surface without coatings. SAR coatings with a contact angle (CA) more than 130° could significantly reduce the ice weight of glass insulators and increase their flashover voltages in the initial stage of the icing process. Coated insulator strings with a CA of 110° showed poorer anti-icing and flashover performances than the bare insulator string.

An OH-PDMS-modified nano-silica/carbon hybrid coating for anti-icing of insulators part ii: anti-icing performance

Icing on insulators affects seriously the operation safety of high voltage transmission lines. Super-hydrophobic and semi-conducting coatings show anti-icing potential for insulators on transmission lines. By combining super-hydrophobicity and electrothermal effects, a hydroxy-terminated polydimethylsiloxane (OH-PDMS)-modified nano-silica/carbon hybrid coating was developed to solve the problem of insulator icing. The anti-icing performance of insulators coated with OH-PDMS-modified nanosilica/ carbon hybrid coating were investigated. Leakage current, temperature distribution, ice morphology, icicle length, and flashover voltage of the insulators are presented. Both the electric and the thermal field distributions were analyzed to verify anti-icing performance of the coating. Experimental results show that the joule heat generated by the coating increases the insulator surface temperature, and the OHPDMS- modified nano-silica/carbon hybrid coating has a superior performance to super-hydrophobic coating in terms of reducing ice accretion and improving flashover voltage of insulators.

AC flashover performance of various types of insulators under fan-shaped non-uniform pollution

Previous simulation and observations showed that, the air flow field at windward and leeward side of insulator string will probably be different if the wind velocity is over a certain value, and thus causing the imparity of contamination degree at the two sides. In this paper, fan-shaped non-uniform polluting method was used to artificially simulate the different pollution severity at windward and leeward side of insulator string. Then, the effects of fan-shaped non-uniform pollution on ac flashover performance of 5 types of insulators were discussed. Test results indicate that, SDD, the ratio SDD of windward to leeward side (W/L), the occupation ratio of leeward side (k), will affect the ac flashover performance of insulator string. U50 and SDD still can be expressed by the negative power function. A reduction in W/L from 1/1 to 1/15 would give a decrease about 23% in a value, which causes U50 reducing about 25%, but n value changes little. The correction method proposed by EPRI is also applicable for fan-shaped non-uniform pollution, but has difference. A larger creepage distance of insulator does not mean that the creepage distance utilization rate is higher. Due to the influence of fan-shaped non-uniform pollution, the existing insulation configuration of transmission lines in heavily polluted areas may not satisfy the required insulation margin. The results have certain reference significance for the design and selection of transmission line external insulation.