A Novel Approach to Roebel Bar Stator Winding Repair in a Large Hydro Pump-Generator

One of the advantages of the Roebel bar type stator winding is that in-service failures of the stator winding can be repaired by replacing the failed bars with spares. On large hydrogenerators, access to the core face to allow replacement of the failed bars can be accomplished by either removing 2-3 rotor poles or by removing the rotor from the stator. This paper will describe an unusual situation in which neither of the normal repair access options were feasible, and how the specific winding failure location and Roebel bar design allowed for a novel approach to repair the winding. The paper will describe the initial testing and inspections performed, the reasoning that led to the novel repair approach, the repair work and in-process testing, the final testing, and observations made when returning the unit to service.