I Incoming line at newly-built 765 kV Sterrekus Substation includes separate corona protection for insulators and hardware.
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photos: Extensive network of dust deposit gauges and insulator reference strings allow pollution environment to be regularly monitored. how it will respond in our service environment. It also means that different insulator creepage values can be specified in the case of a single very long line.”
One example of this type of thinking put into practice is the planned extension to Cape Town of the 765 kV Gamma-Kappa Line. The first 200 km of this 350 km line were insulated with glass strings having 20 mm / kV. However, once the line passes the mountains near the heavily agricultural Ceres Valley, it enters a zone of high pollution and insulation will therefore be changed to composite types with 31 mm / kV.“ Of course”, notes Narain,“ if there is not much difference in acquisition cost between low creepage and high creepage insulation, we might decide
to go with the higher level along the whole route. Environments are dynamic, with possible increases in pollution levels, and we could therefore gain extra security.”
At the same time, he and colleague Vosloo warn that line design engineers must be cautious in specifying high creepage in every situation. Says Vosloo,“ there is an optimized creepage which balances the risks of flashover and ageing. Too low a creepage increases risk of flashover but too high may increase risk of premature ageing.”
With the planned re-structuring of the transmission grid to one based on 765 kV AC and ± 600 kV DC, there is now a big drive to establish a new KIPTS with greatly expanded
“ There is an optimized insulator creepage in the case of every line which balances the risks of flashover and ageing. Too low a creepage increases risk of flashover but too high may increase risk of premature ageing.”
Photos: INMR ©
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