Hydro generators: introduction to stator windings

A variety of stator winding types (coil, bar and concentric) can be found in our hydropower generating units. The lifespan of a winding varies depending on the use, type of insulation (asphalt, polyester, epoxy, B-stage, VPI, etc.), quality of fabrication and installation, and maintenance.

The stator winding is the part of hydropower generating equipment that has the highest operating costs due to equipment price, installation complexity, production loss and risk of unplanned breakage. With the loss of knowledge among most operators and the aging generating fleet, it is imperative to develop a maintenance strategy that incorporates specialized tests and regular inspections/assessments.

Assessing the winding is key to its sound management and extending its remaining service life, its real purpose. Once the condition of the winding is known, there are different strategies available. The complete rewinding of the stator is the most obvious strategy, and it is also the one that requires the most effort and greatest investment.

Other alternatives exist and may prove to be successful strategies for prolonging the winding’s remaining service life at a lower cost and for managing acceptable risk levels. This paper covers side packing, slot wedging, coil jumping, single bar replacement or neutral and phase inversion. We explore these topics both in this publication and in future articles.