New concepts in evaluating electric equipment insulation systems ¿ The problems encountered

ENGINEERS have searched for many years to find suitable yardsticks to evaluate insulation. On a scientific plane, one of the earliest approaches was made by Lamme and Steinmetz in 1912.1 Ultimately, their work resulted in the preparation of AIEE Standard no. 1.2 This Standard outlines the principles underlying the accepted method of classifying electrical insulation material. As long as reliance was placed on the insulating materials that existed in nature, it was reasonable to classify materials on the basis of their chemical composition. But, within the past few years, the chemical industry has made great advances. Today, approximately 350 bonding and impregnating resins known by various trade names are available. With the coming of these chemical investigations and the creation of truly synthetic materials, it is no longer rational to fit existing insulations into the old chemical-composition classes.