NOVELTY - The hydrogenerator has an annular stator (2) for defining an inner stator opening and comprising electrical stator windings (22). An annular rotor (3) comprises a magnetic structure (30) to interact with the windings to generate electrical energy if the rotor rotates relative to the stator. An axial bearing assembly comprises repulsive permanent magnet units (60, 62) to act between the stator and the rotor to axially force the rotor in first direction (64) relative to the stator opposite to second direction (9). An axial stop assembly (66) limits axial movement of rotor in the first direction.    USE - Hydrogenerator for converting water flow energy into electrical energy in a submerged state through electromagnetical components in a stator and a rotor.    ADVANTAGE - The rotor is arranged with an axial surface extending at right angles to an axis of rotation of the hydrogenerator, where the surface rests against an axial surface of the stator under preload of repulsive magnet force so as to generate low friction between the rotor surface and the stator surface to keep the rotor in an angular position relative to the stator when the hydrogenerator is moved during transportation or installation operations, thus reducing mechanical friction losses and ensuring wear-resistance performance of the stator and the rotor, and hence extremely prolonging maintenance-free service life of the hydrogenerator. The axial bearing assembly operates frictionless due to friction between surfaces vanishes for allowing the hydrogenerator with a radial bearing assembly comprising tiltable pads to autonomously start the rotor to rotate from standstill without supplying electrical energy to the hydrogenerator, thus improving working performance of the axial support of the rotor and a radial support. The hydrogenerator ensures that permanent magnet units are easily manufactured and mounted on a support ring, support ring segments and axial surfaces of the stator and the rotor. The hydrogenerator avoids repulsive force between the stator and the rotor while assembling the stator and rotor by applying external force on the rotor relative to the stator to keep the rotor in a position in which the axial stop assembly is arranged. The hydrogenerator utilizes a ring-shaped axial stop element to realize stop effect of the axial stop assembly, thus avoiding tilting of the rotor and the stator relative to each other. The pad is preloaded, so that excessive tilting of the pad with concomitant loss of water lubrication can be avoided.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of a hydrogenerator.    Annular stator (2)    Annular rotor (3)    Directions relative to a stator (9, 64)    Electrical stator windings (22)    Magnetic structure (30)    Repulsive permanent magnet units (60, 62)    Axial stop assembly (66)