In the early hours of January 17, 1994 an earthquake, measuring 6.6 shear wave magnitude on the Richter scale, struck a section of Los Angeles. According to engineers at the municipallyowned utility, damage to the local power system exceeded $ 75 million, especially at the Rinaldi Substation, an important 230 kV switching point in the grid. Apparently, about half of this damage related directly to broken porcelain and in particular post insulators and 500 kV transformer bushings. This prompted the affected utility to begin a serious assessment of applying composite insulators more widely to limit impact of future seismic events.
Aerodynamic glass disc insulators find widespread application in environments such as deserts, where the wind is relied on to do all the natural cleaning due to the absence of rain. However, this photo from a test station in Tunisia clearly illustrates that even these insulators can accumulate significant contamination that remains unaffected by natural cleaning.
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Brittle fracture is a welldocumented phenomenon affecting composite insulator designs whose external sealing mechanism no longer prevents moisture from entering into internal interfaces, typically near the end fittings. The fracture in such instances is typically planar, with smooth surfaces. The recent failure illustrated by this photo, however, occurred near the center of the insulator and seems due to an entirely different and still to be researched mechanism believed related to improper bonding of the housing to the rod.