Analysis of Rotor Winding Faults in Variable-Speed Pumped Storage Units Based on Fractional Harmonic Theory

Rotor winding faults in variable-speed pumped storage units (VSPSU) pose significant challenges for reliable operation and relay protection. This paper presents a novel approach for the detection and analysis of rotor winding inter-turn faults based on fractional harmonic theory. By employing multi-circuit theory, the spatial harmonic characteristics of fault currents are accurately modeled, allowing for precise simulation of internal fault phenomena. Simulation studies demonstrate that fractional-order harmonic magnetomotive forces generated by inter-turn short circuits induce circulating currents with distinct frequency characteristics in the stator windings. Furthermore, the analysis reveals that the amplitudes of fractional harmonics are significantly higher in the low-frequency range, providing a sensitive indicator for fault detection. A protection criterion is proposed, utilizing the ratio of fractional harmonic components to the fundamental component, which effectively distinguishes internal rotor faults from external disturbances and improves the reliability of relay protection schemes. The validity and effectiveness of the proposed method are verified through RTDS-based simulation experiments.