Aging compound Mica — Epoxy resin as a state function

In this paper, aging of the compound mica - epoxy resin used as insulating material in the stator bars of electric machines as a state function based on the dielectric losses and capacitance is discussed. Aging can be defined as irreversible deleterious changes in any material which affects its performance and shortens its life time. State functions are physical quantities whose variation depends on the initial state and the final state of the system and but they do not depend on intermediate forms or the way how this evolves. To this, 15 samples were designed and subjected to Step Voltage Endurance Test (SVET) at a constant temperature of 90°C. Before and during each period of aging, the dielectric losses of each of the sample were measured at a voltage of 2 kV at 20^oC to determine the rates of change in the insulation as the material grew older.