From the standpoint of many utility engineers, it is fair to say that the bushing is probably among the least exciting elements of the modern substation – a basically unchanged, often indestructible component which, in many cases, has outlasted the people who have been involved in its selection and maintenance.

For example, Chuck Nellis, Manager of Substation Design & Maintenance at the Bonneville Power Authority in the U.S. has spent more than 35 years at the utility. Yet he talks about bushings at BPA which are now between 50 and 60 years on the job and which are still not slated for replacement any time soon since they continue to test well. Nellis also remarks that, as far as he can see, there has not been enough change in the appearance of bushings over the past 30 years to attract any special interest or attention.

Yet, for all of its apparent lack of ‘sex appeal’, the bushing still fulfills a vital role in terms of the value of the equipment in which it serves as a component. To use a metaphor: if a transformer were a building, the bushing could perhaps best be described as its lock and key - a relatively small investment protecting the proper function of a very large investment. According to Detlev Gross, Managing Director of Power Diagnostix, a German-based supplier of testing equipment for transformers, bushing failures are one of the most prominent sources of power transformer failure.

To many utility engineers, such as BPA’s Nellis, it may indeed appear that bushing technology has not changed all that much for decades now. However, in reality, most modern bushings have gone through several generations of refinements in areas which are not always apparent to the final utility user.

At the same time, there are now new bushing designs where the differences from traditional looking products are more clearly evident to the casual observer. Typically, these rely on technologies developed comparatively recently - certainly in relation to the long history of bushings production and application.

The General Manager of one of the largest bushing suppliers once remarked, “The industry must work harder to educate users that a bushing is much more than simply porcelain with a copper wire. It is actually quite an involved product.” This special two-part feature article will aim to contribute towards this goal.

Part 1, in this issue, emphasizes the supply side of the bushings business, namely market characteristics as well as the various alternative technologies available. Part 2 – to be published in the November-December issue of INMR – will focus predominantly on future directions and expectations.