Present practise in the design and manufacture of high-tension insulators

Abstract

As considerable time or a severe condition is necessary to show up serious insulator defects, the favorable line conditions on the earlier lines permitted the use of inferior material and designs. The apparently satisfactory operation of inferior insulators together with the large production necessary did much to retard improvement in the insulators, for improvement was practically impossible unless same could be accomplished without materially increasing the cost. The desire to increase production and improve the material necessitated radical changes in the manufacture and equipment, so that the well equipped plant today is far different from the ordinary pottery which it resembled a few years ago. The rapid development in the transmission field has materially changed conditions, and rendered much apparatus obsolete, the early insulator being no exception. As causes of losses have become evident, means have been found to eliminate the serious effects of same. The recognition of the increased value of reliability together with the study of operating conditions has materially changed the insulator situation, so that the material going to the scrap pile today is more suitable for line work than the best product a few years ago. The loss from porosity has been reduced to a negligible quantity by improved firing methods and a closer selection. To prevent the serious cracking loss noticeable on old insulators, has been the most difficult problem. To prevent trouble on old lines, it may be necessary to give the insulators a temperature, as well as an electrical test. Trouble from this source on modern insulators is prevented by careful attention to the temperature gradient, increased mechanical strength to resist internal stresses, and a lowering of the internal stresses by means of an elastic joint. The performance of the modern insulator is very gratifying, and its performance must not be judged by insulators which are really obsolete.