The effect of added impurities on the breakdown voltage of insulating oils. (summary of experimental work.)

This investigation was undertaken to determine the effect of impurities on the electric strength of insulating oils, and the results show that while the addition of moisture or cotton or pressboard fibre causes some diminution of the breakdown voltage, the association of moisture with either of the other two greatly increases the effect. After a considerable amount of investigation, test methods, apparatus and technique, to enable the research to be carried out, were developed at University College under the direction of Sir Ambrose Fleming. The investigation thus inaugurated was continued for the Association by the Metropolitan-Vickers Electrical Co., Ltd. The original programme of tests was very exhaustive and included the investigation of many more impurities than were eventually tried; also the number of oils used was reduced to two as it was found that results obtained with many oils were somewhat similar The numerous tables from the various reports have been omitted from this Summary of the Experimental Work, as the curves contained therein (representative of a large number of measurements) show the results of the investigation. Much of the information previously published is of doubtful value, because it ascribes to one class of impurity effects which have most probably been due to the interaction of two or more.