Inter-strand fault signature analysis in turbo-generators transposed stator bars

This study focuses on the difficulty in identifying subtle fault characteristics caused by inter-strand short-circuit fault within the stator bars of large turbine generators. A multi-section field-circuit coupled finite element model of a single-slot turbo-generator stator bar is established. Based on the results from transient field calculations, the distortion characteristics o f the stator bar end magnetic field and the time-frequency harmonic features under different short-circuit conditions are investigated. The radial magnetic flux density at the midpoint of the stator bar end is extracted, and the variation trends in its magnitude and phase during different types of short-circuit faults are analysed. Wavelet transform is employed to extract the high-order harmonics and inter-harmonics components triggered by unbalanced electromotive forces and magnetic field distortion in the faulted strands post-short-circuit. The differences in harmonic content for short-circuit faults occurring at different positions are compared. Significant differences exist in the changes of stator bar end radial magnetic flux density and current harmonics for inter-strand short-circuit occurring at different axial and radial positions.