A liquid cooling method for a hydroelectric generator which cools the winding of the rotor via a primary cooling liquid circuit, the cooling liquid being maintained in the circuit by the produced centrifugal force. The dissipation of the thermal energy takes place via a secondary cooling liquid which flows once vertically through the system. Accordingly, the thermal exchange takes place via a co-rotating heat exchanger in the center of the rotor. A device for carrying out such a method is also disclosed.