Electrical ageing in lifetime estimation of hydroelectric generator stator windings

Objective of this study is to presents an approach for predicting electrical ageing in the lifetime estimation of hydroelectric generator stator windings. Accelerated voltage endurance tests can be used for new or in-service aged stator bars to estimate electrical ageing. However, sample windings removal from each operating unit are needed for testing, taking several days. Therefore, it is not a practical alternative for analysing large numbers of units. Instead, it was decided to use the electrical ageing model and to match the factors of the model with winding lifetimes in the generator database. Based on the experimental study, it was concluded that in some cases the electrical field stress restricts the targeted winding lifetime. Therefore, it is necessary to include electrical ageing model to estimate the lifetime of stator windings. Additionally, electrical ageing curves for various winding insulation systems were conducted including asphaltic-mica, shellac-mica, epoxy re-impregnated shellac-mica and epoxy-mica.