Modern global vacuum and pressure insulation systems for large high voltage machines

The concept of global vacuum pressure impregnation has been in existence for many years and thousands of motors and generators have been manufactured by this process. Over the past 20 years the unit size of machines manufactured by this process has steadily increased until it is now common for generators having outputs up to 100 MW or more to be impregnated by this means. The introduction of large machines, particularly those having line voltages of 11.0 kV or more, to a process that relies upon coils being fully impregnated in situ requires a precise understanding of the way in which resin penetrates layers of main ground insulation. This paper describes some of the laboratory work carried out in order to ensure complete resin penetration of the winding and compares the respective performance of film and glass backed micapaper under these conditions. An explanation is also given for the necessity for relief planes within insulation systems used on machines having long core lengths