Diagnosis of inter-turn short circuit in excitation winding of pumped storage unit based on frequency-resolved circulation spectrum

The online monitoring of inter-turn short-circuit (ITSC) faults in excitation windings of pumped storage units is easily affected by static air-gap eccentricity (SAGE) and armature response, and the early fault characteristics cannot be easily identified effectively. To address these problems, this study proposes a frequency-resolved circulation spectrum (FRCS) fault diagnosis method for ITSC faults in excitation windings. Firstly, the equation for the same phase multi-branch circulation under SAGE compound ITSC conditions is derived based on the structural characteristics of pumped storage units and electromagnetic induction relations, and obtains the characteristic harmonics of the loop current caused by ITSC faults. Secondly, this study introduces the implementation method of FRCS, considering a pumped storage unit with a generation capacity of 334 MVA as the research object. This study develops a two-dimensional finite element simulation model, calculates the magnitude of the in-phase branch circulation at different fault levels, extracts the corresponding time and frequency domain spectrum and FRCS, and verifies the effectiveness of the proposed method based on comparative experiments. Finally, based on the MJF-30-6 Synchronous Generator Experimental Platform in the Power System Dynamic Simulation Laboratory, ITSC operation at different fault levels is simulated, and the corresponding in-phase branch current data are collected for FRCS analysis. The experimental results demonstrate that the method can effectively eliminate SAGE and armature reaction interference, identify early weak ITSC faults and visualise the severity of faults in the form of pixel dots.