According to executives at some of the largest suppliers in the industry, resin-impregnated paper (RIP) designs incorporating silicone composite insulators today represent the leading edge in bushings technology. The term leading edge does seem fair and reasonable to use in this regard since it implies designs which incorporate the most recent technical advancements in the field. Whatever opinion one holds of these types of bushings, their performance and their expected service life, few can argue that they currently represent the state-of-the-art in new bushing technology.

Yet, although being available now for the better part of two decades, this particular technical solution currently accounts for barely 2 per cent of the total graded bushings market. All RIP bushings – whether with silicone or with traditional porcelain housings - together represent only some 20-25 per cent of the total business.

Rather, the market is still dominated by the stalwart porcelain-housed, oil-impregnated paper (OIP) bushing which has for many years proven itself to be a reliable and long-lasting network component. Given this, it is perhaps not too surprising that there are those in the industry who doubt that this technology will be replaced any time soon, if indeed ever at all.

Giorgio Villa, Managing Director of Italy’s Passoni & Villa, has for nearly three decades served as Secretary of IEC’s Study Committee 36 on Insulated Bushings. Based on the perspective he has had of this business over these years, he remarks, “the (expected) behaviour over time of the OIP dielectric is based on actual service experience supported by years of consistent recorded data.” Such, he claims is not yet the case with alternative newer bushing technologies. “We will still need to wait an extended period,” he says “before reaching the same level of confidence and experience with more recent types of bushings such as resin-impregnated paper, particularly at voltages above 245 kV.” Villa goes on to observe that, in his opinion, the growing interest in RIP technology today is perhaps more based on being ‘in fashion’ rather than on solid technical grounds.