Impact of the saturation on diagnosis of short circuit in the field winding based on the measurement of the magnetic air gap flux

This paper presents the air gap flux measurements during the establishment of the open circuit saturation curve, and load ramp-up of large hydro electrical generator. Experimental data were carried out on three different machines tested at different operating conditions. The advantages, disadvantages, and limitations of the rotor windings diagnostic using the voltage induced by the pole leading edge instead of using the magnetic flux value is analyzed and discussed. New diagnostic features to detect interturn short circuit inside the rotor windings are also introduced.