Electro-thermal ageing in lifetime estimation of hydroelectric generator stator windings

The objective of this study is to present an approach to estimate the effect of electro-thermal ageing in the lifetime estimation of hydroelectric generator stator windings. In the design of hydroelectric generator high voltage stator windings the characteristic electrical field strength can vary significantly leading to various electrical stresses. In addition, the operation temperature of stator windings can vary leading to various thermal stresses. Therefore, it is preferable to take into account the combined electrical and thermal stresses in the lifetime estimation and use the electro-thermal ageing model for lifetime estimation. In this study the parameters for an electro-thermal ageing model of asphaltic-mica and epoxy-mica stator windings were estimated. The operation history of a generator database was used. Based on the estimated parameters, electro-thermal ageing curves for temperature Class A and Class F stator winding insulation systems were developed. On the basis of the results of the study, it is proposed that in the type tests of new insulation systems with high voltage stress a combined thermal and electrical ageing test with both stresses applied simultaneously should be used.