Naikui Gao

Characteristics of dust deposition on suspended insulators during simulated sandstorm

In the present work, we studied the dust deposition characteristics on suspended insulators under the simulated sandstorm conditions in a laboratory. Based on the simulation experiments, the basic dust deposition and distribution characteristics were studied, such as the difference of deposition among sheds at different locations, the difference of deposition between large and small sheds, the relationship between deposition quantity and flow speed of air and dust as well as the relationship between deposition quantity and experimental duration. Our study provides important insights for more advanced studies on this topic in the future.

Investigation of the effects of nano-filler on dielectric properties of epoxy based composites

In this paper, epoxy resin based composites filled with nano-Al<inf>2</inf>O<inf>3</inf> and nano-SiO<inf>2</inf> individually were fabricated. The relationships between the dielectric properties and fillers properties (contents and particle size etc.) were investigated. The results showed that, for nano-SiO<inf>2</inf> filled epoxy, relative permittivity(ɛ<inf>r</inf>) and loss factor(tanδ) increased obviously when filler content was lower than about 0.1wt.%, continue to increase filler content, it appeared a minmium value while filler increased to 0.3wt.%, and above this loading, ɛr and tanδ start to increase again increased with increasing filler content. While for the composites with nanosized Al2O3, a similar phenomenon was observed. The tanδ of epoxy/ micro Al<inf>2</inf>O<inf>3</inf> composites was larger than that of epoxy/ nano Al<inf>2</inf>O<inf>3</inf> composite. Both ɛ<inf>r</inf> and tanδ of Al<inf>2</inf>O<inf>3</inf> filled composites were larger than that of SiO<inf>2</inf> filled composites for its high inherent permittivity.

Flashover characteristics of discrete water droplets on the surface of super-hydrophobic silicone rubber

Super-hydrophobic silicone rubber (SIR) was fabricated by hot-pressing template method, and its surface water droplet contact angle reached 153.5° and sliding angle 8°. The observation of microstructure showed that there were plenty micrometer-scale papillas and nanometer-scale particles on its surface, the mechanism of super-hydrophobicity caused by this micro-nano hierarchical structure was discussed. In order to study the influence of super-hydrophobicity on the electric field distribution, two-dimensional simulation was carried out in software platform ANSYS. The influence of contact angle, volume and location was discussed. The simulation results indicated that super-hydrophobic surface had a better effect of electric field shielding. The flashover experiments (for both single and double droplets on different SIR surface) were carried out and showed that the flashover voltage of super-hydrophobic SIR with droplets on its surface was higher than that of ordinary SIR, which confirmed the simulation.

Preparation and dielectric properties of epoxy/silica nanocomposites

In this paper, epoxy resin based composites filled with nano-silica were fabricated. The relationships between the dielectric properties as well as glass transition temperature (Tg) and nano-filler content were investigated. The results showed that, relative permittivity (εr) and dielectric loss tangent (tanδ) decreased when filler content was no more than 0.3wt.%, and reached minimum value at 0.3wt.%, but above this filler loading, εr and tanδ started to increase with increasing filler content. The DC volume resistivity decreased with the introduction of nano-silica, and the value of Tg did not appear to change significantly with filler content.

The investigation of the wetting behavior on the red rose petal

The study on superhydrophobicity is based on the wetting behavior of droplets on the rough surface. The wetting behavior on the red rose petal was observed by optical microscope at micrometer scale. Results showed that the wetting behavior was dynamic and air moved slowly between the droplet and the red rose petal. Many isolated air cushions were also found at the interface. In order to explain the relationship between the wetting behavior and the high adhesive force on the rose petal, a geometric model about solid-liquid-air three phase interface was proposed. The adhesion on the rose petal mainly depended on the sealed air inside the interface which could not connect to the atmosphere and the strong association of the solid/liquid at Wenzel wetting domains in this model.

Dynamic behavior of water droplets and flashover characteristics on a superhydrophobic silicone rubber surface

In this paper, a superhydrophobic surface is used to increase the flashover voltage when water droplets are present on a silicone rubber surface. The dynamic behavior of a water droplet and the associated flashover characteristics are studied on common and superhydrophobic silicone rubber surfaces under a high DC voltage. On common silicone rubber, the droplet elongates and the flashover voltage decreases with increasing droplet volume and conductivity. In contrast, the droplet slides off the superhydrophobic surface, leading to an increased flashover voltage. This droplet sliding is due to the low adhesion of the superhydrophobic surface and a sufficiently high electrostatic force provided by the DC voltage. Experimental results show that a superhydrophobic surface is effective at inhibiting flashover.

Study of flow-electrical field influence on withstanding characteristics of HV suspension insulators in sandstorm circumstance

In this paper, the withstanding characteristics (differences of withstanding voltage for sub-insulator on different position, influences of electrical field and flow field on withstanding voltage, etc.) of polluted suspension insulators in the sandstorm circumstance were investigated through the simulation experiments in laboratory. The results show that both electrical field and flow field have distinct effects on pollution deposition and withstanding voltage. The greater the electrical field and flow field, the lower the withstanding voltage. In addition, through contrasting the results coming from experiments with and without electrical field, it is shown that the withstanding voltages are distinctly different and the differences have close relationship with the ratio of applied voltage to flow speed. The conclusions of this paper will be helpful to advanced investigation in this field.

Electric Field Calculation of 500kV Cable Terminal and Structural Optimization of Stress Cone

In this paper, the electric field of 500 kV cable terminal is calculated and the influences of stress cone material, structure on its electric performance are researched. The optimal condition is presented that the tangential electric field gradient is equal at the interface between the precast stress cone and XLPE cable insulation. From the calculation and analysis of the electric field distribution at the interface between the precast stress cone and XLPE cable insulation, it can be confirmed that the stress cone structure of 500 kV cable terminal is properly designed with uniform electric field distribution. The calculation and analysis results provide important information for the structural design of power cable terminal

Effect of water absorption on dielectric properties of EPDM/Al(OH)/sub 3/ composites

This paper deals mainly with the effect of water absorption on dielectric properties of EPDM/Al(OH)/sub 3/ composites. The relationship between dielectric properties and water absorption is investigated by accelerated aging. The diffusion coefficient of water in composites is computed, and the mechanism of water absorption of composites is discussed. The results show that permittivity and the loss tangent of the composites is closely related with water content and filler particle size. The filler-polymer and filler-filler interfaces are the main path of water entering the composite, which play an important role in the effect on dielectric properties.

Corrosion resistance and dynamic anti-icing of superhydrophobic surface on ASW

ABSTRACT The superhydrophobic surface (SHPS) with a contact angle (CA) of 151° and a sliding angle (SA) of 0.5° was successfully fabricated on aluminium stranded wires (ASW) via a simple chemical etching process, and subsequently covered with a fluoroalkylsilane film. The wettability and microstructure of consequent SHPS was characterised by CA/SA, scanning electron microscopy and 3D colour laser scanning microscope, respectively. A simple dynamic icing experimental system was performed. The corrosion resistance and dynamic anti-icing property were also investigated by acid/alkaline solution corrosion and dynamic icing test. The results showed that, due to the combined effect of micro-nano structure, air cushion and capillary. The SHPS possessed great corrosion-resistant and anti-icing properties; moreover, the anti-icing property increased by 68.2% and the starting icing time was delayed by six times, which should be critical to the potential application in industry.