Group III Dry-type power transformers - functional temperature endurance tests on a silicone glass fiber insulation system - part II

Experience in presenting a paper on the subject at the 1954 Annual Meeting of the NRC Conference on Electrical Insulation indicates that additional background information on high temperature materials and additional tests on models are desired. Functional testing is rapidly gaining momentum in acceptance. The background of usage of high temperature materials, the importance of remaining practical in establishing a Test Code; the recent action of standardizing bodies in dictating 220°C hottest spot temperature for silicone bonded glass fiber insulation systems, the importance of distinguishing between the grades of silicones now on the market, how aging temperatures originated, the importance of correlating data with transformers in service and actual usage of the same insulation system in transformers in service is outlined in the paper. Barrier insulation of 16 model transformer structures has withstood the severe thermal, humidification and voltage shock when exposed to aging temperatures ranging from 276°C to 325°C, 48 hours to 384 hour cycling at the lower temperature for a total. of 1238 hours aging time. To expect failure by puncture in barrier insulation, it appears that a maximum aging temperature of approximately 350°C, 48 hour duration per cycle, and over five such cycles including humidification and voltage must be used.