Ageing due to thermal cycling by start and stop cycles in lifetime estimation of hydroelectric generator stator windings

The objective of this study is to present an approach to predict ageing due to thermal cycling by start and stop cycles in the lifetime estimation of hydroelectric generator stator windings. In this study a multi-stress electro-thermo-mechanical ageing model was applied for remaining lifetime calculations of stator windings. For various insulation systems the factors of the model were matched with the generator database. Average values and the distribution of lifetime consumption in hours per start and stop cycle are presented for studied asphaltic-mica and epoxy-mica winding insulation systems. Based on the results of the experimental study, it was concluded that there are significant differences between the lifetime consumption values of various generators. It is recommended that simultaneous electrical and, thermal cycling type tests are performed in those cases where the characteristic field stress is relative high.