Insulating paper

In his review of progress in insulation research for 1939, Professor Whitehead (123) states that, while there have been no outstanding new developments in the field of high voltage insulation for power cables, a great deal of information has appeared which concerns existing designs, as well as new methods of test. This statement applies equally well to the specific field of insulating paper with which several of the 84 references included in Professor Whitehead´s review are concerned. Because of a certain amount of overlapping of time covered by these annual reviews, and since reference is frequently made to papers presented orally but not published the same year, some of the work reviewed here has been referred to in the last annual review. Thus, the work reported by F. M. Clark on the deterioration of oil-treated paper in 1938, referred to in last year´s review, has appeared in the March, 1939 issue cf the Journal of Industrial and Engineering Chemistry. In this paper, Clark (124) presents data showing that the behavior of oil-impregnated paper may bear no relation to “bulk” oil tests, as the quantitative proportion of acids formed in the oil may be of less effect than their ability to be adsorbed by cellulose fibers. This problem of the deterioration of impregnated cellulose is also discussed by J. J. Smith and J. A. Scott (125), who, in addition to a review of the literature, present data concerning the aging of built-up samples, 100 mils thick, of both yellow and black varnished cloth and white cotton tape treated with black varnish, over the temperature range from 105 to 200°C. Deterioration was followed by means of visual observation, by bending tests, and by breakdown voltage tests on samples immersed in water. The results have particular significance with respect to the temperature rating of motors and other electrical machines.