Computational Model for Investigating the Influence of Unbalanced Magnetic Pull on the Radial Vibration of Large Hydro-Turbine Generators

Abstract

A radial unbalanced magnetic pull (UMP) can be produced by an eccentric rotor and leads vibrations in large hydro-turbine generators. The influence of nonlinear UMP on the radial vibration of a large hydro-turbine generator is analyzed in this paper. The UMP is determined as a function of eccentricities and field currents by means of a simple analytical method instead of the finite element (FE) method. The analytical method employs the no-load characteristic curve of an electrical machine and saturation effects of the ferromagnetic materials are taken into consideration. FE rotor model of a large hydro-turbine generator unit, taking account of guide bearings, thrust bearing and periodic forces, is developed to investigate the influence of UMP on radial vibrations. The FE rotor model and the analytical method for UMP constitute the computational model. UMP is calculated under different rotor eccentricities and field currents by the proposed method. Comparing with other analytical methods, the effectiveness of the proposed method is verified. Dynamic responses of the FE model under different analytical methods for UMP are calculated to investigate the difference in vibration between different analytical methods. A simulated excitation test is performed and a comparative analysis between the calculated results and the field data is provided. The computational model is proved to be reasonable according to the analysis.

Dynamic Model for Hydro-Turbine Generator Units Based on a Database Method for Guide Bearings

“…Unbalanced magnetic pull (UMP) is an electromagnetic originated force due to the non-uniform air-gap flux density around the rotor circumference. An analytical method has been proposed to calculate the unbalanced magnetic pull, which is taking account of field current and saturation effects [12]. Taking advantage of the method, effect of field current on vibration could be investigated.…”

Nonlinear dynamics of a novel fractional-order Francis hydro-turbine governing system with time delay

“…Nagode and Skrjanc [8] proposed a dynamic model of a Francis hydro-turbine with a surge tank, and realized a fuzzy power control approach to determine unknown parameters. Xu and Li [9] using the analytical method built a finite element rotor model and investigated the influence of unbalanced magnetic pull on the radial vibration of large hydro-turbine generators. However, considering that the HTGS is essentially a complex nonlinear, time-variant and non-minimum phase system [10,11] , previous researches with integer order calculus have some limitations on reflecting the real vibration mechanism of the HTGS.…”

“…Thus, the study of the stability of the HTGS becomes necessary and urgent. Fortunately, there are many contributions to the modeling of the HTGS and corresponding stability analyses based on the integer order calculus [5][6][7][8][9] . For example, Lai [7] studied the hydraulic stability of a Francis hydro-turbine by using numerical simulation.…”

Analysis of Nonlinear Dynamic Characteristics of a Mechanical-Electromagnetic Vibration System with Rubbing

“…In Gustavsson et al [19]'s paper, the influence of nonlinear magnetic pull was studied for a generator where the generator spider hub does not coincide with the center of the generator rim; Perers et al [20] studied the mechanism of unbalanced magnetic pull generated by a synchronous generator with static eccentricity, and discussed the influence of iron saturation on the magnitude of magnetic pull. Lundström et al [21] analyzed the influence of the rotor and stator shape deviation on the dynamic characteristics of the generator, and proved the importance of the unbalanced magnetic pull nonlinear influence; Calleecharan et al [22] proposed a rotor model considering radial and tangential unbalanced magnetic pull forces; Xu et al [23] studied the effect of UMP on radial vibration of hydroelectric generators, and compared and analyzed the simulation results and the field experimental data; Zeng et al [24] established the hydro turbine generating sets dynamics model by using the unbalanced magnetic pull force acting on the generator and the unbalanced force acting on the rotor as the input excitation of the hydro turbine generating sets system; Xu et al [25] established a hydro-generator dynamics model considering the nonlinear unbalanced magnetic pull force and the linear water unbalance force; Xu et al [26] studied the response characteristics of unbalanced magnetic pull rotor system considering both static and dynamic eccentricity. Xiang et al [27] analyzed the influence of unbalanced magnetic pull on the nonlinear dynamic characteristics of permanent magnet synchronous motors rotor system; Li et al [28] established a two-dimensional hydroelectric generator electromagnetic model, using the finite element method to study the characteristics of the electromagnetic flux and electromagnetic force; Yan et al [29] analyzed the influence of excitation current on the nonlinear dynamic behaviors of the generator.…”