Evaluation of mechanical integrity for water cooled generator stator windings in power plants

One of the critical points, when the reliable operation of water-cooled generator is concerned, is the mechanical integrity of stator windings. The resonance of stator winding will occur when the intrinsic frequency of each stator winding equals or closes to excitation frequency, 120Hz, due to an electromagnetic force which occurs always during the normal operation. This resonance may cause the leak of cooling water and / or the life reduction of generator stator due to the high cycle fatigue crack. This paper describes the modeling of generator stator end windings for analysis of the winding vibration behaviors. The result of the analysis has a good agreement with that of field test. A mechanical diagnostic method is also suggested and applied to 500MW water-cooled generator stator in order to evaluate the mechanical integrity of stator end windings in power plant. It was found that the vibration characteristics of poor windings in terms of resonance possibility could be improved through the blocking of end windings.