The vibration on the stator core of hydrogenerators caused by electromagnetic forces is an important factor affecting the reliability and long-lasting operation of a machine. For a suitable addressment of the problem, it is necessary to accurately predict the eigenmodes and eigenfrequencies of the mechanical system. However, different results for the eigenfrequencies can be achieved depending on the applied model and material parameters. This work contributes to solving this issue by investigating the impact of different input parameters on the eigenmodes and eigenfrequencies calculated by analytical and numerical models. The results are discussed and compared to measurements performed on a prototyped 732 kVA hydrogenerator.

The stator core vibration caused by electromagnetic forces is an important topic in the design of electric machines. A crucial task for the comprehensive analysis of this issue is to accurately estimate the eigenmodes and eigenfrequencies of the mechanical system, which allows the calculation of the forced mechanical response. This paper presents a new analytical model based on beam elements as an alternative to the typical finite-element (FE) and classical analytical models applied for this purpose assuming a 2D simplification of the system. The proposed model takes the stator yoke and teeth into account and is able to predict the eigenmodes, eigenfrequencies and forced response of the stator core of rotating electric machines, such as synchronous and induction motors. The results are compared to FE and analytical calculations and validated based on measurements on the stator core of a permanent magnet synchronous motor.

The calculation of magnetically induced vibrations in the stator of an electric machine involves, on the one hand, the determination of the magnetic forces originating from the air gap field and, on the other hand, the calculation of the mechanical eigenmodes and eigenfrequencies. This work presents a new method for the mechanical modelling of the stator using shell elements in 3D, as an extension of a recently published method using beam elements in 2D. It is applied to the case of a hydro generator with a complex mechanical construction, including the frame, and the results are validated by measurements performed on a 55MVA machine. It is shown that the developed method allows a time-efficient calculation of the eigenmodes and eigenfrequencies, providing an advantageous alternative to the classical analytical and finite element (FE) methods typically used for this purpose. This outcome is particularly relevant and applicable to the design and optimisation of large electric machines, as well as troubleshooting vibration problems in existing machines.

Structural vibrations caused by magnetic forces in synchronous machines constitute a multi-domain problem involving both electromagnetic and mechanical phenomena. Recent years have seen an increasing effort in the scientific community to improve the capabilities of the calculation models used to assess this problem. On the one hand, this trend contributes to increasing the accuracy of the calculated results obtained. But, on the other hand, the increased complexity of the models tends to make the identification of cause-effect relationships more difficult. In this context, this work proposes a new graphical tool for the comprehensive analysis of stator core vibrations in synchronous machines. The development of a holistic diagram for the root cause analysis of the electromagnetic and mechanical phenomena, called the vibration cause diagram (VCD), is presented and applied to two example machines of different sizes. The analysis method obtained is particularly useful during the design phase of a new machine or for the troubleshooting evaluation of the existing machines.

The vibrational behaviour of the stator of a hydro generator is an important aspect to be evaluated during the design of the machine, as it has an impact on its maintenance and life expectancy. This evaluation requires, in addition to the calculation of the exciting magnetic forces, the determination of the eigenfrequencies and eigenmodes of the stator structure. This task is particularly challenging for a large hydro generator due to its structural complexity, involving various components such as the laminated core, the ventilation air ducts, the frame, the winding, and the connections between these. This paper is dedicated to the experimental investigation of the influence of the stator winding on the mechanical eigenfrequencies of the stator assembly. For this purpose, a series of experimental modal analyses is performed in different assembly phases of a real 55 MVA generator. It turns out that, from the stator's point of view and by considering the typical winding insertion methods without global impregnation, the winding is only weakly coupled to the laminated core. Thus, the mass and the stiffness of the winding have no substantial effect on the system's eigenfrequencies. This finding contributes to the selection of appropriate simplifications and assumptions in the modelling of the complete stator including the winding for the prediction of structural vibrations in future works.