Thermal evaluation of dry-type transformer insulation systems

The concept of accelerated functional testing of insulation materials and systems got great emphasis near the start of the second half of this century. This interest was spurred on when Dr. Dakin¹ illustrated that insulation deterioration conformed to the Arrhenius chemical rate equation. The American Institute of Electrical Engineers (AIEE), recognizing the importance of this concept, organized the working groups to develop test procedures for the thermal evaluation of insulation materials and systems. One such group was the Working Group on Life of Insulating Materials of the AIEE Transformer Committee. This Working Group was assigned the task of developing functional test methods for evaluating the permissible operating temperature of insulating structures in dry-type transformers. A subgroup of this Working Group published a proposed test procedure ² for trial use in 1956. This test procedure primarily covers high voltage transformers of the core-form type. Most of the work with this procedure was reported prior to the time the test procedure was published.