An electric generator for a wind turbine including: a stator having a plurality of segments (S1,..., SN) circumferentially extending about a longitudinal axis of the stator, an electrical circuit associated with said segments (S1,..., SN), the electrical circuit including a plurality of coil windings respectively wound on said segments (S1,..., SN), each coil winding including an electrical insulation, wherein the electrical circuit comprises a plurality of current sensors for measuring currents flowing in the electrical circuit, wherein the electric generator includes a controller for receiving current signals (111, 112, 113) from said current sensors, calculating parameters depending on an impedance of at least a portion of said electrical circuit, determining a status of the insulation of a portion of the electrical circuit, wherein each segment (S1,..., SN) is associated with a respective current sensor of the electrical circuit for measuring a current flowing in the coil windings and determining a status of the insulation of the electrical circuit; characterised in that the controller comprises an extraction block, the extraction block comprising a difference calculation block configured to calculate a difference (Δ) of the input current signals (111, 112, 113), a band-pass filter configured to calculate harmonics of the difference (Δ) of the input current signals (111, 112, 113), and a first calculation block configured to generate a diagnostic signal based on amplitudes of the harmonics; and/or the controller comprises an extraction block, the extraction block comprising a band-pass filter configured to calculate harmonics of the input current signals (111, 112, 113), and a second calculation block configured to calculate a variation of a phase (δ) of the harmonics with respect to a reference angle signal and to generate a diagnostic signal based on the variation. a stator having a plurality of segments (S1,..., SN) circumferentially extending about a longitudinal axis of the stator, an electrical circuit associated with said segments (S1,..., SN), the electrical circuit including a plurality of coil windings respectively wound on said segments (S1,..., SN), each coil winding including an electrical insulation, wherein the electrical circuit comprises a plurality of current sensors for measuring currents flowing in the electrical circuit, wherein the electric generator includes a controller for receiving current signals (111, 112, 113) from said current sensors, calculating parameters depending on an impedance of at least a portion of said electrical circuit, determining a status of the insulation of a portion of the electrical circuit, wherein each segment (S1,..., SN) is associated with a respective current sensor of the electrical circuit for measuring a current flowing in the coil windings and determining a status of the insulation of the electrical circuit; characterised in that the controller comprises an extraction block, the extraction block comprising a difference calculation block configured to calculate a difference (Δ) of the input current signals (111, 112, 113), a band-pass filter configured to calculate harmonics of the difference (Δ) of the input current signals (111, 112, 113), and a first calculation block configured to generate a diagnostic signal based on amplitudes of the harmonics; and/or the controller comprises an extraction block, the extraction block comprising a band-pass filter configured to calculate harmonics of the input current signals (111, 112, 113), and a second calculation block configured to calculate a variation of a phase (δ) of the harmonics with respect to a reference angle signal and to generate a diagnostic signal based on the variation.