A method of determining a fault condition in a synchronous machine. The method includes a) obtaining a field current signal and a shaft voltage signal of the synchronous machine, b) transforming the field current signal and the shaft voltage signal to obtain a field current frequency spectrum and a shaft voltage frequency spectrum, and c) determining whether a fault condition is present, and in case a fault condition is present identifying a type of the fault condition, based on harmonic content of the field current frequency spectrum and harmonic content of the shaft voltage frequency spectrum, wherein c) includes comparing the harmonic content of the field current frequency spectrum with fault condition field current signature spectra and comparing the harmonic content of the shaft voltage frequency spectrum with fault condition shaft voltage signature spectra.