The object of this Test Procedure is to establish a method for estimating by comparison the life expectancy of specialty transformer insulation systems under actual operating conditions. The electrical insulation of specialty transformers is made up of many different components selected to withstand the widely different electric, mechanical, and thermal stresses occurring in different parts of the structure. How long an insulation system will be serviceable depends on the effectiveness of the physical support for the insulation, and the severity of the forces acting on it, as well as on the materials themselves and the service environment. Therefore, the length of useful life of the insulation system will depend on the way that its individual components are arranged, their interactions upon each other, and the contribution of each component to the electrical and mechanical integrity of the system. It is the intent of this Test Procedure to have each component of the composite structure operate and perform during the test under conditions which are similar to actual operating conditions in the transformer, modified only as necessary to accelerate failure. Prolonged exposure to high temperature is the principal aging factor employed in these tests. Other tests such as mechanical stress, exposure to moisture, and voltage have been chosen in such a way as to develop and disclose promptly any significant weakness or deterioration of the insulation system