Drying out of a 11 kV-4900 kVA Synchronous Machine through Different Methods

The moisture content is a critical parameter in the insulation of all the electrical machines, from oil-transformers to dry rotating machines. In the case of synchronous machines, drying out is a usual practice, especially hydro generators. In case of a low value of the insulation resistance or a low value of the polarization index the machine should be dried out. This paper presents the experience in drying out a 4900 kVA, 11 kV, brushless synchronous machine by two different methods.