Air-cooling is the most common way of cooling large generators like those used in hydropower. However, because these machines are quite complex and therefore, understanding the cooling of these machines is not easy. The details of the air flow inside of the generator is still a field in which the academics are doing research and developing more detailed and accurate CFD studies. The downside of these CFD studies is that they often involve the use of more computational resources and time. This lack of versatility of CFD studies makes its use impossible for daily small design tests. In this area, the lumped parameter thermal models are the tools used to get fast and good enough results that allow designers to test little modifications. The present work consist of the development of a versatile lumped parameter model, implemented in Matlab/Simulink, to study the cooling of hydro-generators from a thermal and fluid perspective, contributing to future ventilation studies and research. The model created is based on a 3D network modelling of a Voith Hydro real generator, using lumped element strategy and is able to run transient simulations in a very short amount of time. The model is validated with real thermal data and is finally used to perform a parametric study of the outlets of the stator cooling ducts of the modelled generator.