The use of polyester film in HV rotating machine insulation

Mica remains, after over 100 years, the predominant material used to insulate high voltage rotating machines; however, to aid its application; mica has always required a supporting material. The drive today is for HV rotating machine insulation to be subject to continuous improvement and to achieve higher performance. This has not only resulted in significant changes to supporting materials, but has also seen major developments in the methods of application. Established manufacturing processes and design technology have therefore had to be critically reviewed and some seemingly fundamental unshakeable concepts eliminated or changed. Work on polyester films has shown that when used as part of a composite insulation system the results have been initially surprising; being comparable and possibly in some instances better than those obtained with established supporting materials. Detailed is the use of polyester film/micapaper composite tapes both as stator coil conductor/turn and main wall insulation in resin rich and VPI systems. Finally the relative performance of different films is reviewed and the need for improved characteristics, such as that of increased thermal conductivity, is considered.