Evaluation of the change in winding pattern of a large hydro generator

Uprating and refurbishment of large hydro generators presents opportunities for increase in power output, efficiency and life time of the machine. Several parts of the machine can be changed depending on the need and predicted performance outcome. For the generator unit in this paper, refurbishment of the stator winding is to be done while maintaining the same stator core design, therefore a new winding pattern is proposed for the machine. This paper numerically compares the proposed new winding pattern and the old winding pattern using flux density distribution and radial electromagnetic forces in the air gap. Emphasis is given to the low frequency harmonics with the potential to excite the natural frequency of the core, causing noise and vibration. The calculated total harmonic distortion (THD) of the new winding pattern is higher than the old winding pattern by 3%. This was reflected in the increased damper bar and core losses in the machine with the new winding pattern.