Numerical and Experimental Study of the Ventilation in an Operating Hydrogenerator

In this paper, a three-dimensional CFD simulation of the air flow in a 14.4 MVA hydrogenerator in service at EDF is performed. This machine was selected because it presents a large axial temperature gradient in the stator core that imposes some load limitations. The computational domain includes all the main components of the hydrogenerator (rotor, stator, frame and housing) except for the coolers since they would require a much higher meshing and computational effort. The numerical results show a significant axial flow maldistribution across the stator ducts with a flow blockage in the bottom duct that is most probably responsible for the overheating observed in the bottom region of the stator core. This finding has been validated through air flow measurements that were performed at the outlet of several stator ducts using a custom sensor developed at Hydro-Quebec's Research Institute. Furthermore, the computed windage losses in the hydrogenerator were compared with the measured ones and a discrepancy lower than 1% was found. Consequently, this numerical investigation has successfully proven the capability of a CFD model to reproduce the ventilation anomalies present in an operating hydrogenerator, as long as the input parameters of the model are carefully fixed. Moreover, this approach can provide engineers with useful information that could help them solve cooling issues.