Spectral Attribution of Electromagnetically Induced Stator Vibration in a Hydro-Generator

Electromagnetic force is an important excitation source of stator-core vibration in hydro-generators. The methodological novelty of this study lies in an order-specific spectral-attribution framework for electromagnetically induced stator vibration. Unlike conventional electromagnetic–structural analyses that focus mainly on response-amplitude prediction or resonance screening, the proposed framework links electromagnetic-field distribution, Maxwell stress-based force harmonics, experimentally validated modal frequencies, swept-frequency harmonic response, and normalized modal detuning to distinguish force-dominated components from components influenced or amplified by nearby structural modes. A full-scale three-dimensional electromagnetic model of an actual hydro-generator was established to calculate the electromagnetic surface force acting on the stator-core tooth surfaces. The electromagnetic-force spectrum was obtained using fast Fourier transform. The steady-periodic surface-force data were converted into complex harmonic load vectors through Maxwell–Mechanical coupling and mapped onto the structural model as distributed surface loads, while hammer-impact modal tests were used to validate the structural dynamic model. With an electrical fundamental frequency of 50 Hz, the force spectrum contained components from approximately 49.9 to 499.2 Hz, corresponding to the first ten electrical-frequency orders. The principal vibration responses occurred near 9.98, 99.78, 199.56–201.55, 299.33, and 399.11–399.16 Hz. The minimum modal detunings of the 4th-, 6th-, and 8th-order electrical-frequency components were 4.02–4.97%, 1.81%, and 2.41–2.42%, respectively. Accordingly, the 4th-order component was identified as a dominant electromagnetic forced response with possible influence from the 210 Hz mode, the 6th-order component exhibited modal amplification associated with the 294 Hz mode, and the 8th-order component was influenced by the nearby 409 Hz mode. Although the 9th- and 10th-order force components were present, their vibration responses remained weak. These results demonstrate that the vibration spectrum is shaped jointly by electromagnetic excitation and structural frequency-response effects, providing a quantitative basis for electromagnetic-source reduction, structural detuning, and damping enhancement.