Method for monitoring, including detecting, internal winding faults, especially inter-turn faults, of a synchronous generator, which synchronous generator comprises a winding (20, 23, 26) for each phase (a-c) of a power network, a terminal (5a-c) for each phase (a-c) arranged on a terminal side of the synchronous generator, and connected to the respective winding, the terminals (5a-c) on the terminal side is connected to an electrical power network, and the synchronous generator is arranged to input power to the electrical power network by means of the terminals, the method comprising: measuring (301, 501) the voltage (V a, V b, V e) of each phase at the at least one each terminal and the current (I a, I b, I c) of each phase at the terminal, determining (302, 305, 306, 502-506) whether the synchronous generator suffers from an internal fault especially inter-turn faults in any of its phases, wherein the determining includes; transforming (302, 502) the phase currents (I a, I b, I c) and the phase voltages (V a, V b, V c) into symmetric sequence currents (I 1, I 2, I 0) and symmetric sequence voltages (V 1, V 2, V 0), respectively; monitoring (305, 505) at least one of the following variables: a negative sequence residual voltage (ΔV 2); a zero sequence residual voltage (ΔV 0); a negative sequence coupling impedance (Z 2C); a zero sequence coupling impedance (Zoc); wherein each of the variables is calculated from symmetric sequence components (I 1, I 2, I 0, V 2, V 0) and at least one generator specific impedance (Z 00, Z 22), and determining (306, 504, 506) whether the synchronous generator suffers from a winding fault, or not, from the calculated at least one residual voltage (ΔV 0, ΔV 2) or coupling impedance (Z 0C, Z 2C); the method further comprising an additional internal fault detection step including analysing the rotor field winding current of the synchronous generator. measuring (301, 501) the voltage (V a, V b, V e) of each phase at the at least one each terminal and the current (I a, I b, I c) of each phase at the terminal, determining (302, 305, 306, 502-506) whether the synchronous generator suffers from an internal fault especially inter-turn faults in any of its phases, wherein the determining includes; transforming (302, 502) the phase currents (I a, I b, I c) and the phase voltages (V a, V b, V c) into symmetric sequence currents (I 1, I 2, I 0) and symmetric sequence voltages (V 1, V 2, V 0), respectively; transforming (302, 502) the phase currents (I a, I b, I c) and the phase voltages (V a, V b, V c) into symmetric sequence currents (I 1, I 2, I 0) and symmetric sequence voltages (V 1, V 2, V 0), respectively; monitoring (305, 505) at least one of the following variables: a negative sequence residual voltage (ΔV 2); a zero sequence residual voltage (ΔV 0); a negative sequence coupling impedance (Z 2C); a zero sequence coupling impedance (Zoc); wherein each of the variables is calculated from symmetric sequence components (I 1, I 2, I 0, V 2, V 0) and at least one generator specific impedance (Z 00, Z 22), and a negative sequence residual voltage (ΔV 2); a zero sequence residual voltage (ΔV 0); a negative sequence coupling impedance (Z 2C); a zero sequence coupling impedance (Zoc); wherein each of the variables is calculated from symmetric sequence components (I 1, I 2, I 0, V 2, V 0) and at least one generator specific impedance (Z 00, Z 22), and determining (306, 504, 506) whether the synchronous generator suffers from a winding fault, or not, from the calculated at least one residual voltage (ΔV 0, ΔV 2) or coupling impedance (Z 0C, Z 2C); the method further comprising an additional internal fault detection step including analysing the rotor field winding current of the synchronous generator.