Extension of the post impregnation concept to high voltage windings

The past decade has witnessed increasing utilization of the post impregnation concept of processing stator windings. The projections initially made as to the ability of post impregnated windings to, endure against moisture, chemical, and other unfavorable environments have been substantiated by prolonged and varied service experience(1,2). Limitations imposed on the extent of post impregnation processing have been 1) physical size of motors exceeding the handling capacity of the manufacturer's equipment, and 2) voltage rating, the higher voltage windings necessitating more stringent attention to power factor requisites and methods of suppressing corona discharges at coil insulation surfaces. While these electrical requirements deserve particular attention in the design of high voltage insulation to avoid premature degradation, the windings are subjected to the same environments as lower voltage windings, and the insulation system must be adapted to provide integral protection against unfavorable operational conditions. If materials and processing used for the lower voltage windings could be adapted to accommodate the particular requirements of high voltage insulation, it would result in a high voltage system with a proven degree of physical reliability. By incorporating a proven system, assurance of physical and environmental endurance could be accepted on the basis of service experience, obviating the need to extrapolate from accelerated laboratory simulations. By defming the requirements and using a system approach, an insulation system for post impregnation processing of motor windings up to ratings of 15,000 volts has been developed and is in current use.