If one studies the evolution of composite insulator technology since its development starting in the 1970s, one fact quickly becomes clear: the market experience for apparatus insulators has been much different than for line insulators.
For example, composite insulators for overhead lines were initially received with great interest by power supply companies due to their promised advantages of superior pollution performance as well as lightweight combined with high strength. However, this initial enthusiasm soon evaporated once users became aware of the accompanying risk of mechanical failure and dropped conductor – a failure mode labeled brittle fracture that reached its peak during the 1990s.
To some extent, mechanical fracture of the core rod is still being encountered today, especially with older generations of line insulators or with units that have been damaged during handling or produced without proper quality control. Nevertheless, after intensive research, most experts now believe that the cause of this problem is well understood and that modern composite line insulators are designed and manufactured to virtually eliminate such a risk. Composite hollow core insulators, on the other hand, have never suffered from any single documented mode of failure. On the contrary. Service experience has, by and large, confirmed that this technology offers the high performance expected across most applications, assuming of course that the insulators were properly specified for their service environment.
Nonetheless, in spite of positive field experience, the rate of application of composite hollow core insulators until now has proven much slower than for their ‘cousins’ operating on overhead lines.
One of the reasons for this is that, unlike line insulators that are typically specified and purchased directly by the power companies or turnkey line contractors, equipment insulators are usually ordered by the OEMs of breakers, transformers, switches, etc. For these types of customers, the main purchase considerations have always been cost as well as a guaranteed long service life. Here, competition from porcelain has proven challenging, especially at the lower transmission voltages where the greatest volumes are required.
Yet, in spite of having lagged behind expectations for years now, the application of hollow core composite insulators finally seems on the verge of growing rapidly – some predict even exponentially. While in 1993 only tens of thousands of units were estimated to be in service, that population has soared and now numbers well over a million, with most installations taking place in just the last several years.