Insulation failure mechanisms on large rotating machinery

Electric machines include essentially rotating and stationary elements, each of which contains conductors, a magnetic circuit and insulation. The electrical insulation determines the reliability to a marked degree. The insulation structure is complex in nature wherein the various parts are required to withstand mechanical, dielectric and thermal stresses. The nature of the stress depends upon operating conditions, physical size of the machine, the machine component and other design factors. Operating conditions include the type of service such as continuous duty versus cyclic, ambient conditions including possible exposure to contaminating influences.