In the context of more electrical aircrafts, Permanent Magnet Synchronous Machines are used in a more and more aggressive environment. It becomes necessary to supervise their health state and to predict their future evolution and remaining useful life in order to anticipate any requested maintenance operation. Model-based prognosis is a solution to this issue. A generic modeling framework is proposed in this paper in order to implement such a prognosis method which relies on knowledge about the system ageing. A review of existing ageing laws is presented, and motivates the choice to developp an ageing model that could incorporates every kind of ageing laws. A generic ageing model is then defined, that allows representing the ageing of any equipment and the impact of this ageing on its environment. It includes the possible retroaction of the system health state to itself through stress increase in case of damage. The proposed ageing model is then illustrated with Permanent Magnet Synchronous Machines. A fictive but realistic scenario of stator ageing is built. It comprises apparition and progression of an inter-turns short-circuit and its impact on stator temperature, which value has an impact on the ageing speed. A prognosis method based on the generic ageing model is proposed, and applied successfully to this scenario.