Abstract <p>Among various methods of diagnostics of the technical condition of synchronous generators, contactless diagnostics with assessment of the stage of defect development without decommissioning electrical installations, connecting sensors, and measuring devices to assess the technical condition, and interfering with the design of synchronous generators seems a promising approach. The method of detecting internal defects of a synchronous generator based on the analysis of changes in the distribution of the external magnetic field that occurs during its operation is considered. A model experiment showed that, in the presence of faults, the amplitude and spectrum of the field change. Based on computer modeling using the finite element method, electrical and mechanical defects are identified by analyzing the external magnetic field of the synchronous generator. Diagnostic signatures of defects in the stator and excitation windings, as well as the static eccentricity of the inductor, are determined, and the degree of development of these defects is shown. The method can be used to diagnose the technical condition of not only synchronous generators, but also electrical machines of other types.</p>