Problems with modern air-cooled generator stator winding insulation

Modern stator winding design and manufacturing methods have been successful in reducing the costs of turbine generators. Problems such as thermal cycling, coil abrasion in the slot and PDs in the endwinding have lead to failures after as little as five years of operation. To avoid premature failures, users of modern air-cooled machines should ensure they have a good purchase specification, are present at the factory for critical phases of machine manufacture, operate the machine within specification, keep the windings clean, and closely inspect the stator winding after about one year of operation. The latter is much more important than it was for hydrogen-cooled machines. Although some problems cannot be corrected, effective means are available to slow down the deterioration process, if the problems are discovered at an early enough stage.