A Combined Approach Based on Experience and Technique for Stator Bars Repair in Hydro-Generators

This paper presents advanced techniques for the repair of stator bars in hydro-generators. Damaged stator windings are one of the critical issues that can occur in generators. Although monitoring has improved, winding failure is difficult to predict. It might even be impossible to predict when it is due to various mechanical damages, and it could lead to a long unplanned maintenance. Today’s techniques of design and production of stator bars are well known. When it comes to damages caused by phase-to-phase fault or mechanical damages due to rubbing to existent stator bars, there is no universal decision criterion or repair method, and many factors must be considered before moving forward with a repair. It is therefore a big challenge to apply the right (optimum) solution to reduce production losses. Decision criteria for evaluation of the viability of a repair based on damage location, severity, and bar operation voltages are discussed based on many years of experience on hydro-generators winding repairs. A method of repairing insulation from mechanical damages due to rubbing to winding bars without the need to remove the bars is proposed. Evaluation of this repair method is performed using common acceptance tests. Finally, it will be shown that it is possible to quickly return a generator back to service after a major stator winding damage with adapted repair methods using comprehensive mitigation of risk techniques.