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.
Effects of biological contamination on insulator performance
Results of investigations on biological growths on different insulators, especially porcelain and silicone rubber ones, are presented. The insulators have been exposed to tropical weather under polluted and clean conditions in Sri Lanka and Tanzania since 1995. Algae contamination was found on the insulators at the clean locations. The algae were identified as green algae. After performing a series of laboratory tests, it was concluded that the effect of algae was not too strong on the contaminated silicone rubber insulators. Suggestions how to control the algae growth are presented.
DESIGN CONSIDERATION TO PPM KLYSTRONS FOR INDUSTRIAL LINAC
Toshiba has been developing the C-band and X-band Periodic Permanent Magnet (PPM) focused klystron in collaboration with KEK and manufactured prototypes for the JLC project. [1] The PPM klystron has an advantage to enhance the total efficiency as a result of eliminating the electric power for the focusing magnet. From experience on the development the PPM focused klystrons for the JLC project, we plan to apply the PPM focused klystron to the medical and industrial linac. The periodic magnet focusing scheme has some technical difficulties such as stop band voltage. To design the PPM klystron for the medical and industrial linac, it is necessary to give heed to electron beam instability; so that the tube parameters of the PPM focused klystrons have some constraints. The size of the accelerator system is substantially reduced if a PPM focused klystron is used. The majority of medical and industrial linacs use frequencies of S-band range. We discuss the availability of the S-band PPM focused klystron in this paper.