A flux-based technique is proposed for the on-line detection, localization and discrimination of stator and rotor turn-to-turn faults in synchronous generators, using the measured air-gap rotational magnetic field. Simple magnetic field sensors (MFSs) are installed in the stator slots at different regions, and the corresponding induced voltages are measured. Several differential voltages are then obtained to give a picture of the rotational magnetic field symmetricity, whose distortions indicate the presence of the stator or rotor faults. The proposed diagnostic technique is presented in detail and validated initially by simulation results obtained with a finite element simulation package and afterwards through the experimental tests. The obtained results demonstrate that the proposed technique can be used to detect and discriminate stator and rotor turn-to-turn faults with appropriate sensitivity. In addition, the region of the stator turn-to-turn faults can be identified as well.