Stator Deformation of Large Hydrogenerators and Its Effects on the Machines

This paper is about the evaluation of a stator roundness of hydrogenerators in some of the EDELCA´s hydroelectric complexes in Venezuela. During the operation of these units, high values of current unbalance between neutrals/groups in parallel per phase were found. Complete vibration measurements of units were performed and normal values were obtained. In addition air gap and displacement of stator bases were measured and it was found that some of the sliding bases were stacked, not allowing the stator to keep its round shape for the operation. Due to magnetic unbalance caused by a non uniform air gap, the effect on the rotor structure was investigated on a generator of 250 MVA at Macagua Power Plant applying finite elements analysis. As a conclusion, limits for stator roundness were established to avoid fatigue on rotor spider structure as a consequence of the cycling forces caused on the rotor structure at the rotating speed frequency