Abstract: A system for ventilating a rail traction motor and for dynamically purifying the ventilation air, the system comprising a centrifugal fan (1) having radial blades (2) surrounded by a circular housing (3) and delivering air to the motor, and dynamic filter means on the path of the air delivered by the fan. The system includes a plane sheet (4) pierced by peripheral through openings (5) forming a diffusing screen and dividing the inside volume of the circular housing into an upstream chamber (6) connected to the air inlet of the fan, and a downstream chamber (7) connected to its outlet leading to the motor, an exhaust outlet (8) for exhausting impure air, the exhaust outlet being in the form of a sector on the periphery of the upstream chamber, and a separator element (9) disposed facing the opening and forming an obstacle to deflect air streams close to the blades of the fan towards a take-up section close to the exhaust opening.