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| Electromagnetic Vibration Analysis and Suppression of the Operating Large Hydro-Generators Based on Stator Coils Open-Circuit |
| Zhao Xiaolong1, Zeng Yuhao2, Kang Haoyu1, Yang Yong2, Wang Jin1, Zhou Libing1 |
1. State Key Laboratory of Advanced Electromagnetic Technology Huazhong University of Science and Technology Wuhan 430074 China;
2. Dongfang Electric Machinery Co. Ltd Dongfang Electric Corporation Deyang 618000 China |
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Abstract In large hydro-generators, spatial magnetic field harmonics induced by complex stator-rotor interactions may excite pronounced pole-frequency electromagnetic vibration, threatening long-term structural integrity and safe operation. For in-service units, conventional mitigation approaches—such as structural reinforcement or rotor/stator re-machining—are often infeasible due to high retrofit costs, long downtime, and risks associated with altering the electromagnetic-mechanical coupling characteristics. To address these challenges, this paper proposes a practical, non-invasive vibration-suppression strategy based on open-circuit stator coils, which locally modifies the magnetomotive force（MMF）distribution without altering the original stator and rotor structures.
The physical mechanism and potential influence of coil removal are first examined, including the resulting spatial MMF discontinuities and the possibility of generating additional sub-harmonics. A semi-analytical electromagnetic force wave model is developed using the stator MMF distribution, air-gap permeance characteristics, and Maxwell's stress tensor formulation. This model enables simultaneous identification of inherent and newly induced MMF harmonics and accurately reconstructs the resulting electromagnetic force spectrum. By correlating force-wave frequencies with the stator-frame coupled natural frequencies, critical excitation components are extracted. Subsequently, a quantitative contribution analysis is established by projecting the spatial MMF harmonic vectors onto the direction of the target electromagnetic force waves, accounting for amplitude, phase, space-time order, and their combined interaction mechanisms.
Then, a multi-objective optimization framework is formulated to minimize the weighted amplitudes of key MMF harmonics. The optimization incorporates essential electromagnetic and operational constraints, including three-phase symmetry, balanced parallel branches, modular submachine periodicity, and restrictions on the allowable number of open-circuit coils. As a result, the optimized coil-removal configuration suppresses the targeted dangerous harmonics such as（12, 2fe), while avoiding the generation of undesired low-order harmonics—typically the major drawback of non-standard phase-belt approaches. Two representative Pareto-optimal solutions are analyzed to illustrate the trade-offs between harmonic mitigation capability and the risk of introducing new harmonics.
The proposed method is validated through finite element simulations and full-scale field experiments on a large hydropower station generator. Simulation results show that the optimized open-circuit configuration reduces the radial electromagnetic force density of the dominant（12, 2fe）component from 7.6 kN/m2 to 2.7 kN/m2, corresponding to a 64% reduction. The associated stator vibration amplitude decreases from 16.2 mm/s to 5.2 mm/s. Field tests demonstrate that the overall 100 Hz electromagnetic vibration amplitude is reduced from 18.3 mm/s to 4.1 mm/s, a 77.6% reduction without generating new significant vibration components. The consistency among analytical predictions, finite-element analyses, and measurements confirms the method's robustness and accuracy. Additionally, the absence of dangerous low-order harmonic force waves in the optimized scheme verifies the effectiveness of the multi-objective optimization constraints.
The stator coils open-circuit strategy provides a highly feasible, economical, and engineering-friendly solution for vibration suppression in in-service hydro-generators. By offering precise harmonic regulation with minimal structural intervention, the proposed method significantly enhances the applicability of electromagnetic vibration control in large hydropower units, providing a reference for future improvements in the grid-supporting capability and operational reliability of renewable energy equipment.
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Received: 09 September 2025
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2026, Vol. 41 
