Zhihai Xu

Anti-icing performance of RTV coatings on porcelain insulators by controlling the leakage current

Considerable work has been done on preventing ice formation on insulators and the modification of the surface characteristics by increasing the contact angle and decreasing the adherent force have been tried with some degree of success. Heating by electric current has however proved to be an effective and practical method for de-icing transmission lines, but difficult to apply to insulators. A room temperature vulcanized (RTV) silicone rubber coating containing sufficient carbon black to render it partially conducting but not enough carbon to lose its surface hydrophobicity, has been investigated to determine if the heat generated would suffice to inhibit ice growth on the insulators. The heat exchange progress was analyzed and the leakage current through it to prevent ice forming was estimated and coatings developed accordingly. The anti-icing performances of these RTV silicone rubber coatings with different leakage current magnitudes were compared in a climate chamber. The results showed that the surface heating effect, together with the hydrophobicity, could significantly reduce the formation of ice on insulators.

Development of RTV Silicone Coatings in China: Overview and Bibliography [Feature article]

The development of room temperature vulcanized (RTV) silicone coatings in China began in early 1985. Over the course of time, they have come to be widely used in China. At present, nearly 800,000 kg of RTV coatings are used every year. They have successfully prevented serious pollution flashover of traditional glass and porcelain insulators and radically reduced the costs of maintaining transmission lines in polluted areas. RTV silicone coatings have been extensively studied in China. The main aspects of the research include improvements in the properties of the formula for better adhesion to porcelain and control of leakage current, the hydrophobicity transference mechanism, and aging. These decades of research have successfully promoted the development of RTV silicone coatings in China. The history of the development and research of RTV silicone coatings in China are discussed in this article.

Study of anti-icing performance of insulator strings bottom-coated with semiconductive silicone rubber coating

Prevention of icing flashover on transmission lines has become an important problem. A new method for mitigating effects of glaze ice on energized insulators has been developed. Semiconductive silicone rubber was painted on the bottom of suspension disc insulators, while the upper ceramic surface was untreated. An electrically conductive path was formed when supercooled water or droplets bridged the uncoated areas. The power loss was limited when there was no precipitation. The heat and partial discharge energy generated by the leakage current melted the original ice accretion on the insulator surface. The electrical performance of the insulator string with this kind of coating under freezing rain conditions was comparable with that of a clean insulator string. The impact of the ambient temperature on the anti-icing performance was also evaluated. In addition, the performance of the insulator with bottom surface semiconductive coating under fog conditions was compared with an uncoated string.

Guiding Effect of Surface Electric Field of Collector on Deposited Electrospinning Fibers

Collecting the fiber mats with uniform characteristics is a current technological bottleneck to industrial application (e.g. filter media, nano-sensors, separators of Li-ion batteries etc.). This paper provides a promising industrial method for collecting uniform fiber mats in large area. The simulation results demonstrated that different collection targets had different surface electric field distribution. The experiments gave a result that thinner and more uniform fibers were collected when using a specific spherical-hat target uniform surface electric field distribution, and the thickness of fiber mats was more uniform as well. The paper presents that the collectors surface electric field has great effect on the electrospinning fibers arrived at the collector, and higher electric field intensity can guide the orientation of the deposited electrospinning fibers.

Comparisons of fibers properties between vertical and horizontal type electrospinning systems

The electrospinning system mainly has vertical type and horizontal type according to the geometrical arrangements of ejecting capillary and collection target, where vertical type includes shaft type and converse type. The fibers were obtained in several kinds of typical electrospinning parameters by using three different electrospinning systems. The SEM was used to observe the morphology of fibers, and then the diameters were measure based on the SEM images by IMAGEJ image analysis software. Additionally, the statistic data were analyzed on the basis of Origin software. The differences of fibers diameters and fibers mats morphology between the three electrospinning systems were gained. The results showed that in the shaft type system, the electrospinning fibers were the thinnest because the gravity can strengthen the effect of electric field to make the fiber extend sufficiently, but it had the widest size distribution of fiber diameter; in the converse type system, the fibers were the thickest and the size distribution was the narrowest; in the horizontal type system, the average fiber diameter and size distribution were between the shaft type and the converse type. Therefore, the geometrical arrangements can be selected according the applied need, which may be thinner fiber diameters or more even size distribution. The paper will facilitate to select suitable electrospinning system in the future application. Key words: electrospinning, PVDF, vertical type, horizontal type, fibers

Exploration of melt-electrospinning based on the novel device

The melt-electrospinning setup was designed in this paper. The temperature of every part in the setup,, including injector, nozzle, spinning space and collection target can be measured accurately by thermocouple or infrared radiation thermometers. The study on phenomena and properties of exploration for melt-electrospinning based on the novel device was conducted. The polypropylene was chosen for the material of melt-electrospinning. The effects of nozzle temperature (T2) and spinning space temperature (T3) on the fiber diameters were mainly analyzed in this paper, and the experimental results showed that the average fiber diameters decreased with the increase of temperature (T2 or T3). The minimum fiber with diameter 4.472 µm was gained in our meltelectrospinning. The unique morphology of fiber mat was observed in the electrospinning system due to the influence of electric field of heating plane.

Impact of surface characteristics on the micro process of ice formation

Ice accumulation on insulator strings and power transmission lines cause serious accidents in many cold regions around the world. The progress of ice accumulation is profoundly affected by surface characteristics such as hydrophobicity and surface heating. This paper focused on the process of ice formation on various kinds of surfaces, such as smooth glass and silicone rubber. A certain kind of semiconducting RTV silicone rubber that can generate heat was also been investigated. The effects of anti-icing were compared. The results showed that the surface heating effect, together with hydrophobicity, apparently affected the pattern of ice.

An application of RTV with different conductivities in anti-icing

The volume resistance of RTV silicone rubber was adjusted by adding conductive fillers. By applying RTV silicone rubber with different conductivities to the different parts of an insulator, the electric field distribution was configured to reduce ice forming at the shed. Experimental results showed that the icicles on the coated porcelain insulators were notably shortened compared with those of uncoated porcelain insulators, and the reasons were discussed.

The Study on Fabrication of Insulated Membrane by Electrospinning

The poly (vinylidene fluoride) (PVDF)/ N, N-dimethylformamide (DMF) solution was taken for example to fabricate insulated membrane by electrospinning in this paper,. It was found experimentally that in the process of electrospinning, the area of membrane collected was bigger and bigger and the fiber diameter was increasing from the bottom to the surface, but the fiber diameter of every layer was uniform. The reason was analyzed in this paper, and it was considered that in the electrospinning process, the positive charges accumulated on the insulated membrane changed the electric field distribution. As a result, the area increased and the weakened electric field intensity increased the fiber diameter.

Thermal and voltage distribution along insulator strings with semiconducting RTV coatings

Icing problems led a great damage to the power network over the world recent years and a lot of ways dealing with this problem are proposed. Semiconducting RTV coating applied to insulators was first put forward in 2007 and it makes a significant role in defeating the ice accretion on insulator surface. Its main advantage in anti-icing are combination of hydrophobicity and hydrophobicity transfer based on the ordinary RTV and the Joule heating effect created by the leakage current. This paper focus on the distribution of voltage and the heat effect of the semiconducting RTV applied to suspension insulator during freezing condition. The thermal distribution along the insulator string with semiconducting RTV coating applied with service voltage in cold condition is investigated using an infrared FLIR. And the distribution of the 7-units 110kV insulator strings is calculated by using finite element analysis. Results showed that the range of the resistance of the semiconducting RTV applied on insulator as a coating is about 106∼107 Ω can get a suitable temperature rise during the cold condition and the voltage distribution is uniform with semiconducting RTV.