A uniform method by which the thermal endurance of electrical insulation systems for dry-type specialty and general-purpose transformers can be compared is established. These insulation systems are intended for use in the types of transformers described in NEMA ST 1-1988 and NEMA ST 20-1992.

The intent of this standard is to establish a uniform method by which the life of specialty transformer insulation systems can be compared. Thermal degradation is generally one of the major factors affecting the life of most insulating materials. It was chosen to be the major environmental factor in this standard. O+ her environmental factors, such as vibration, thermal shock, and moisture, have been included to simulate operating conditions. These factors have been chosen in such a way as to develop and disclose promptly any significant weaknesses during the temperature aging of an insulation system. This standard is offered as a guide for preparing samples, conducting tests, and analyzing results.