Photos: INMR ©
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Greater weight in power engineering almost always translates into higher costs for handling and foundations. It is also a major factor in designing for good seismic performance. This photo, captured at ABB’ s Micafil bushings plant in Switzerland during the mid 1990s, shows in an instant one of the principal advantages of composite insulators over traditional porcelain housings. Here, a middle aged worker easily transfers a housing from stock to the final assembly area on his shoulders. Of course, most such factories are equipped with forklifts for other purposes but not having to rely on them, as in this instance, demonstrates production flexibility.
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The glass suspension string in this photo is in operation in southern Spain. Yet most experts will agree that this unusual arrangement of different profiles offers no real benefit, except perhaps under icing, which is not a threat in this particular service environment. Against risk of flashover from bird streamers, the configuration is less than ideal since the wider aerodynamic profile would then be better placed at the top of the string. As for pollution performance, the two profiles will accumulate different contamination levels due to their different geometries, which in turn will negatively impact even distribution of E-field. While under clean conditions the result might not be too worrisome, depending on similar hardware on both types, the obvious question is‘ why do it at all?’, especially since aerodynamic glass discs are usually more costly.
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Widespread pollution flashovers under winter fog conditions were the principal factor driving application of millions of silicone composite insulators on Chinese transmission lines, starting in the 1990s. This nighttime image from South China provides excellent photographic evidence of how such flashovers can develop along glass tension and jumper support strings.
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Photo courtesy of Transelectrica
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Composite bushings made with liquid silicone rubber typically offer excellent hydrophobicity to help performance in heavily-polluted service environments. This image from such an installation near the Black Sea in Romania, however, shows what can happen if the insulation is not properly dimensioned in terms of specific creepage and shed geometry. Still, while this erosion may look menacing, there are methods to repair damaged silicone housings, as for example have been used in New Zealand on silicone DC cable terminations that suffered similar fates.