Theoretical research on short circuit fault of rotor inner winding in large turbo generator

This paper analyzes the rotor magnetic potential distribution of one large turbo generator both in normal and rotor inner winding short-circuit fault states. By the influence of short fault, the second harmonic current of the stator winding will induce one half and one two-third harmonic currents to the stator winding and the rotor winding respectively. Furthermore, it also analyzes theoretically the effect of inter-turn short circuit on characteristic parameters, which include the stator current, the stator voltage, the rotor current, the rotor voltage, and the active/reactive power. Then a method is proposed to predict or identify different practical faults in details, which is on the base of the relative variation laws of those characteristic parameters varying with the severity of the rotor inter-turn short circuit fault. The fault criterion of rotor inter turn short-circuit on-line identification has been investigated, which can estimate different types of faults. Finally, theoretical analysis based on simulation in Simulink/Matlab is carried out by using the dynamic short-circuit model of large turbo generator units. This paper could give good guidance for the judgment of the rotor inner winding short-circuit fault of large turbo generator by the right choice of characteristic parameters.