Determination of Accelerated Thermal Aging Effect on Dielectric Strength of Dry-Type Transformers Insulation

The service life of high voltage transformers is mainly decided by the life of their solid insulation. These devices need to be monitored continuously throughout their life time. The health assessment of large power rating devices avoids the fire hazards which are originated from thermally stressed solid insulation, and improves the service life time. In the present paper, the effect of thermal stress on the dielectric strength of several insulating papers which are used in dry type transformers has been investigated. Thermally upgraded Kraft, Nomex-410 and Nomex-910 were thermally stressed at higher temperatures in a temperature ranging between 900C and 2400C. Subsequently, the data are analyzed and the effect of thermal stress on the life of dielectric materials is assessed by using simple regression technique. It has been determined that Nomex-910 has the better withstanding capability at high temperatures as compared to that of other insulating materials. The present aging analysis extracts the withstanding capability of several insulating materials at high temperatures. It also helps the industry people in predetermining the health status of insulation.