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Reliability of transmission lines resulting from insulator design selection criteria

The selection of the most appropriate insulator design for any given transmission line application follows rules which might not always be set on technical merits.

Traditional practice, local manufacturing and nearby available supply, procurement cost considerations among other non-technical reasons can modify the initial approach from engineering, and possibly the long-term performance of a transmission line. In each technology, either porcelain, glass or polymer, variations in design and manufacturing processes will ultimately lead to differences in long term performances.

A quick review of the key technical differentiators in every design of insulators will be proposed to help understand the ultimate expectations in terms of reliability and resilience.

Likewise, technical decisions have sometime been made based on solving a specific problem and the collateral consequences are not always examined with a long-term vision. A typical example is illustrated with the classical decisions process linked to pollution management. It has appeared worldwide clearly in the last 10 years that composite insulators, especially when used in harsh conditions might fix the pollution related flashover problems, but at the cost of a much shorter life expectancy. The real challenge is then to establish the overall full life cycle cost including replacement, inspection and possible risks of failures associated. An example will be presented showing a real field case for which pollution problems were solved with polymers with a necessity to replace the insulators after approximately 15 years. The interesting outcome is the evaluation of the TOTEX, the risk analyses in terms of reliability and how maintenance costs are impacted by short term decisions. Often utilities discover that the yearly maintenance cost for cheap purchased goods is a burden defeating the initial cost which goes unseen from the initial investment.

As an alternative, this paper will summarize the key features required to be effective in the mitigation of pollution using silicone coated insulators offering simultaneously the hydrophobicity of silicone (which mechanism will be reviewed) and the strength resilience and longevity of toughened glass insulators. Key elements in the selection of silicone coated insulators will be presented as well as performance measured in the laboratory or from the field in various environments worldwide.

Page 2 of 8 Additionally, an innovative approach to preventive maintenance using smart grid solutions integrated to insulators will be presented. This technology already in place in several countries is providing a real time indicator of the pollution status of insulator strings in severe contaminated environments. These devices benefit the grid maintenance groups to forecast their actions in the field.

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