RIS & RIF Transformer Bushings by Robert Middleton

A transformer bushing functions to safely transfer power through the earthed transformer tank. Oil-impregnated and resin-impregnated paper type bushings have been the industry standard for decades and have generally performed satisfactorily. However, as transformer assets age, deterioration of the paper in originally supplied bushings can cause failure, sometimes even catastrophic. As a result, there is increasing movement these days toward silicone insulated, dry type, paperless condenser bushings that can offer improved safety, no risk of leaking oil, optional maintenance requirements and lower installation weight. Indeed, several suppliers now offer this new bushing technology, which is referred to as resin-impregnated synthetic (RIS) – the common generic terminology for dry, paperless bushings. Resin-impregnated fiberglass (RIF) is the registered trademark of a dry, paperless insulation style of bushing that broadly falls within the RIS category yet is itself a distinctive technology. Introduced in 2003 and with more than 22,000 units installed worldwide, it has greater service experience than the RIS bushing, first launched in 2014. This presentation reviews differences between RIS and RIF type bushings in terms of technology and also how the condenser core is manufactured.