Hydrophobicity and insulated resistance of composite insulators with biological contamination
Biological growth has been observed on insulators installed all over the world. However its impact on the electrical performance is not well known. This paper described the investigations on the performance of post insulators with biological growth at a converter station. Both the ceramic and composite insulators were investigated. Two kinds of biological agents, lichen and mold were found on the composite insulator surface, but interestingly, no biological agent was found on the surface of ceramic insulators in the same environment condition. Lichen concentrated on the upper surface and mold on the lower surface. It seemed that the impact of lichen growth on the hydrophobicity is low, but hardly no hydrophobicity when mold growth. In addition, the insulated resistance test was carried out on the biologically contaminated insulators with and without salt water. Results show that whatever the surface was dry or not, high resistance were obtained with only less biological agent growth at the edge of insulators, but declined sharply when most of the surface was covered with lichen and mold. Therefore, it is strongly recommended to remove the mold, with which most the insulator surface is covered.
Performance of nonceramic insulators under tropical field conditions
This paper presents the results of investigations on the performance of nonceramic insulators in tropical field conditions. Six different types of 33 kV insulators (silicone rubber, EPDM composite, porcelain, and RTV coated porcelain) were installed at six different test sites exposed to marine, industrial and clean environments in Sri Lanka and Tanzania. The visual scrutiny, hydrophobicity class (HC) and surface conductivity were used for the evaluation of the field performance. The silicone rubber and RTV coated insulators preserved the hydrophobic properties although some biological growth was found on them. The EPDM insulators showed distinct surface changes. At the same time, damage due to dry-band arcing appeared on the porcelain insulators exposed to marine pollution.
Diversity of Electrospinning Approach for Vascular Implants: Multilayered Tubular Scaffolds
Abstract The biomimetics of biological structures found in nature remains one of the most promising approaches to engineer functional tissues from natural or synthetic biocompatible materials for the replacement of damaged or injured parts of the human body. Recently, medical therapeutic regimes have advanced into a new era, overcoming the known mechanical and biological variances that occur when using autologous or synthetic grafts. Basically, the core concept of tissue biofabrication, commonly referred to as tissue engineering, is to find out the favorable cellular microenvironments to grow a living tissue prior to clinical uses. In fact, the ability of stem cells to regenerate is controlled via signaling pathways (growth factors) and supporting materials (scaffolds) that guide the cellular activities. After the first successful experiments to fabricate polymer fibers from their solutions, Cooley proposed the use of an electric field a century ago (Cooley (US 692:631, 1902 ). The electrospinning technique has been continually developed as a fruitful polymer processing technique to draw ultrafine nonwoven fibers. Electrospun polymer fibers have been used for a wide range of technical and biotechnical applications such as filtration, organic solar cells, tissue engineering, and drug releasing implants. In this regard, this review begins with an overview about the various spinning approaches for the fabrication of polymer fibers as well as the basic principles of electrospinning process. In addition, this review will highlight vascular bypass surgery and, in particular, the needs for vascular tissue engineering. Finally, the review includes some of the latest attempts to improve the mechanical and biological properties of electrospun polymeric fibers and summarizes the challenges and prospects for the future. Lay Summary However, vascular defects are treated successfully via bypass surgical bypass grafting using autologous or synthetic vessels. The small-diameter vessels (less than 6) are often associated with high failure rate. This review reports some of the recent features that should be highlighted to fabricate an ideal graft for small-diameter vascular grafts. The review introduces multilayered conduits as an alternative approach to overcome the known mechanical and biological mismatches of single layered vascular grafts of electrospun polymers.